Cubic Feet Calculator

How to Calculate Cubic Feet

That is the whole calculation. To calculate cubic feet you measure the three dimensions of a rectangular space, make sure all three are expressed in feet, and multiply them together. The order does not matter. Length × width × height gives the same answer as height × width × length because multiplication is commutative. What does matter is the unit. If you multiply 120 inches by 72 inches by 24 inches you get a number in cubic inches, not cubic feet, and it will be 1,728 times too large. Convert first, multiply second.

The shape this cubic feet formula describes is a cuboid, also called a rectangular prism: six flat faces, every corner a right angle. Rooms, crates, raised beds, truck bodies, trenches and slabs are all close enough to cuboids that this is the right approach for them. Curved and tapered objects need a different formula, and those are covered further down the page.

Worked example: a storage crate measuring 10 ft long, 6 ft wide and 2 ft high. Multiply 10 × 6 to get 60 square feet of floor area, then multiply that by the 2 ft height. The crate holds 120 cubic feet, about 4.44 cubic yards, or 3.40 cubic meters.

One measuring habit saves most of the errors people make here: write the unit down next to every number as you take it. A tape reading of "8" is meaningless a day later, but "8 in" is not. It is also worth measuring to the nearest inch rather than rounding to the nearest foot, because a rounding error in one dimension is multiplied by the other two. Three small roundings can shift a bulk material order by a noticeable margin.

Cubic Feet From Other Units

Tape measures rarely read in whole feet, so most real calculations start in another unit. Each tab below gives the conversion factor for one unit, plus the shortcut for converting the finished volume instead of the individual dimensions. Both routes reach the same answer, so use whichever suits the numbers you already have.

Mixing units is fine as long as you normalise before multiplying, and the calculator at the top of this page does exactly that: it converts every dimension to feet internally, whatever combination of units you pick, then multiplies. A trench measured 12 ft long, 30 in wide and 0.5 m deep is a perfectly valid input.

Square Feet to Cubic Feet (Area to Volume)

If you already know the square footage of a floor, patio, bed or driveway, you do not need to re-measure anything, you only need the depth. To convert square feet to cubic feet, multiply the area by the depth or height expressed in feet. A 400 sq ft room with a standard 8 ft ceiling contains 3,200 ft³ of air. A 400 sq ft border covered 3 inches deep needs only 100 ft³ of material, because 3 inches is a quarter of a foot.

That second example is where nearly every mistake happens. Material depths are quoted in inches while areas are quoted in square feet, and multiplying 400 by 3 instead of by 0.25 overstates the order twelvefold. The chart below removes the arithmetic: find the depth you plan to use in the first column, read across for its value in feet, and multiply your area by that number instead.

Reading one row in plain words: a 6-inch depth is 0.5 feet, so every 100 square feet you cover at that depth consumes 50 cubic feet of material. Scale it however you like, 250 sq ft at 6 inches is two and a half times that figure, or 125 ft³.

The reverse direction is just as useful. Divide a known volume by the area to find what depth it will actually achieve: 60 ft³ of mulch spread over a 300 sq ft bed gives 0.2 ft, which is only 2.4 inches, thinner than most planting guides recommend. Our area-to-volume calculator runs both directions and accepts area in square feet, square yards or square meters.

Cubic Feet to Cubic Yards

• 27 ft³ is exactly 1 cubic yard, divide by 27 to convert, multiply by 27 to reverse it
• 9 bags of standard 3 ft³ bagged material to equal a single cubic yard
• 1 yd³ typical supplier minimum for a loose bulk delivery
• 5–10% margin usually added to a bulk order for settling and spillage

Reading those four figures together: 27 cubic feet is one cubic yard, which is the same quantity as nine three-cubic-foot bags, and roughly the point at which suppliers will take a loose order at all. The reason 27 is the magic number is geometric rather than arbitrary, a yard is three feet long, and a cubic yard is three feet in all three directions, so 3 × 3 × 3 gives the 27 cubic feet inside it.

Everything a bulk supplier quotes flows from that one number. Ready-mix concrete, topsoil, screened gravel, decorative bark and excavated spoil are all sold by the cubic yard, while the bags stacked on the same yard's shelves are labelled in cubic feet. Knowing your requirement in both units tells you immediately which side of the threshold you are on, under roughly 27 ft³, bagged material is normally the cheaper and simpler route, and above it the loose delivery wins on price per unit.

The table below expands the same conversion across the range you are likely to order in, from a single cubic foot up to a 500 ft³ bulk load, with the metric equivalent alongside.

Reading the 27 row across confirms the headline figure and adds the metric column: one cubic yard is also about 0.76 cubic meters. Read the 100 row and a hundred cubic feet turns out to be a little under four cubic yards, the point at which most people stop counting bags and phone a supplier. Because bulk material settles and compacts, apply the ordering margin above to whichever row you land on rather than ordering the exact calculated figure. Step through the arithmetic in either direction on the cubic yard conversion page.

Volume Formulas for Other Shapes

Length × width × height only works on shapes with square corners. The seven cards below cover the non-rectangular volumes people actually need to work out, round tanks and pipes, domes, tapered hoppers, gable roof spaces and rounded-end vessels, each with its formula and the measurement it depends on. Take every dimension in feet and the answer comes out in cubic feet directly.

• Cylinder

  V = πr²h

  Water tanks, sonotube footings, drums and pipe runs. Measure the radius across the flat circular end, square it, then multiply by π and the height.

  Round tank volume tool →

• Cube

  V = s³

  A cuboid with every edge the same length, so one measurement does the whole job. Packing cubes, sample blocks and bale sizes fit this pattern.

• Sphere

  V = 4/3 πr³

  Domes, floats, ball valves and pressure vessels. Radius is half the widest measurement across the shape, taken through its centre.

• Cone

  V = 1/3 πr²h

  Stockpiles of sand or gravel, hoppers and funnels. A cone holds exactly one third of the cylinder that would enclose it.

• Pyramid

  V = 1/3 × base area × h

  Tapered roof cavities and hipped structures. Work out the rectangular base area first, then take a third of it multiplied by the vertical height.

• Triangular Prism

  V = ½ × b × h × length

  Gable attic space, wedge-shaped trenches and ramps. Find the triangular end area, then extrude it along the run.

• Capsule

  V = πr²h + 4/3 πr³

  Propane and air-receiver tanks with domed ends. Add the straight cylindrical middle to the two hemispherical caps, which together make one sphere.

In practice most awkward objects are a combination of these primitives rather than a single one, a grain silo is a cylinder with a cone on top, a water heater is a capsule. Work out each part with its own formula and add the results together. The complete formula reference carries a worked example for every shape listed here, including the compound cases.

Calculating Irregular Shapes (L-Shapes)

An L-shaped room, an alcove kitchen or a wraparound cabinet cannot be measured with a single length and width, but it does not need any advanced geometry either. Draw a line across the shape to divide it into two plain rectangles, calculate each one on its own, and add the two volumes together. This divide-and-sum method scales to any number of sections, a U-shape splits into three, a stepped foundation into as many as it has steps.

Where the depth or height changes between sections, a room with a dropped ceiling over part of it, or a trench that deepens along its run, treat each section completely separately with its own height figure. The only rule is that the sections must not overlap. If you find yourself measuring the same square of floor twice, move the dividing line rather than adjusting the numbers.

Shapes with a curved edge can be approximated the same way, by treating the curve as a series of narrow rectangles, or handled properly with the round-shape formulas covered above. For a bay window recess, splitting the floor plan into a rectangle plus a half-cylinder gets you closer than either approach alone.

Cubic Feet for Landscaping

Garden materials are ordered by volume, not by area, so the question "how many cubic feet of soil do I need" always comes down to two figures: the area you are covering and how deep the layer has to be. The four cards below give the depth each material is normally laid at, and why that depth is the one to use. Multiply your bed area in square feet by the depth in feet, and you have the cubic feet to order.

• Soil

  6–8 in for beds

  Roots need loose, uncompacted depth to spread sideways. Anything shallower than six inches dries out fast in summer and limits what you can grow to shallow-rooted annuals.

  Estimate a topsoil order →

• Mulch

  2–4 in top layer

  Two inches is the minimum that suppresses weeds; beyond four inches the layer holds too much moisture against stems and starts to rot them.

  Work out bark coverage →

• Gravel

  3–4 in drive · 6 in drainage

  A driveway surface course needs enough depth to stay locked together under vehicle weight, while drainage runs and French drains want a deeper bed to keep water moving.

  Size a stone delivery →

• Compost

  2–3 in top-dressing

  Applied as a surface dressing rather than a fill, compost is worked in gradually by rain and worms. A thicker layer smothers surface roots instead of feeding them.

Putting the cards to work: a 4 ft by 12 ft raised bed filled to 8 inches needs 4 × 12 × 0.6667, which is 32 ft³ of soil, around eleven of the three-cubic-foot bags, or just over a cubic yard loose. The same bed later top-dressed with 2 inches of compost needs a further 8 ft³, and the surrounding 150 sq ft of border mulched at 3 inches takes 37.5 ft³ of bark on top of that.

Two adjustments are worth making before you order. Bagged soil and compost settle by roughly ten to twenty percent once watered, so a bed filled exactly to the brim on delivery day will sit low by the following week. And loose material delivered by the yard is measured before compaction, which is why a soil calculator in cubic feet should be treated as a floor for the order rather than a ceiling.

Cubic Feet for Construction

Concrete, fill and excavated spoil are all priced and delivered by volume, so the four numbers below do most of the work on a small build. They are the figures worth committing to memory before you phone a supplier.

• 0.45 ft³ yielded by one 60 lb bag of mixed concrete
• 2.2 60 lb bags needed per cubic foot of finished concrete
• 27 cubic feet in the cubic yard ready-mix is sold by
• 4 in typical thickness for a residential patio or shed slab

Reading those figures together: because a 60 lb bag yields about 0.45 ft³, you need roughly 2.2 bags for every cubic foot, and about 60 bags to make a single cubic yard. That last number is usually the moment a project tips from bagged mix to a ready-mix delivery, mixing sixty bags by hand is a long day, and the concrete has to be placed continuously to avoid cold joints between batches.

Slabs

A slab is a flat cuboid, so the standard formula applies with thickness as the height. A 12 ft × 10 ft patio poured at 4 inches works out at 12 × 10 × 0.3333, or 40 ft³, just under 1.5 cubic yards. Poured at 5 inches instead, the same slab jumps to 50 ft³, which is a useful illustration of how sensitive volume is to depth.

Footings and trenches

Footings are long, narrow cuboids and are calculated the same way: trench length × trench width × pour depth. A 40 ft perimeter footing 16 inches wide and 8 inches deep comes to 40 × 1.3333 × 0.6667, or about 35.6 ft³. Where a footing turns a corner, apply the divide-and-sum approach from the L-shape section so the corner is not counted twice.

Fill dirt and excavation

Excavated soil expands when it is dug out, a phenomenon called bulking or swell, typically by fifteen to thirty percent depending on the soil type. A 100 ft³ hole therefore produces noticeably more than 100 ft³ of spoil to cart away, and filling that same hole back in takes more than 100 ft³ of imported material once it is compacted. Size skips against the swelled figure and deliveries against the compacted one.

These figures are for estimating material quantities only. Slab thickness, reinforcement and footing depth for anything structural are set by your local building codes and site conditions, check the requirements that apply where you are before you order.

Run the numbers for a specific pour with the slab and footing estimator, or size an earthworks order with the excavation volume tool, which factors swell into the delivered quantity.

Cubic Feet for Appliances

Appliance capacity is measured from the interior cavity, never the exterior cabinet. A refrigerator standing 70 inches tall and 36 inches wide does not have 70 × 36 × depth of usable space, insulation, the compressor housing, door seals and shelving supports all sit inside that footprint. This is the single biggest source of confusion when people try to work out a refrigerator's cubic feet from a showroom tape measure, and it is why the manufacturer's rated figure is always smaller than the box it arrives in.

To measure it yourself, empty the compartment and remove the shelves, then take the interior width, depth and height in inches. Multiply the three and divide by 1,728. Fridges with separate freezer compartments are rated by adding the two cavities together, which is why spec sheets often list fresh food and freezer capacity on separate lines before giving a combined total.

Reading the table as a rule of thumb, the usual planning figure is four to six cubic feet of fresh-food capacity per person in the household, which puts a family of four squarely in the standard 18–26 ft³ band. Stepping up to a French door model buys width and organisation more than raw volume, the capacity gain over a large standard unit is often only a few cubic feet.

The same interior-cavity principle governs other appliances. Washing machine drums are rated between roughly 2.0 and 6.0 cubic feet, with 4.5 ft³ and above counting as a large-capacity machine able to take a king duvet. Dishwasher tubs and microwave cavities are quoted the same way, and in every case the number describes what you can load, not the space the appliance occupies in the room. Compare specific models against your alcove with the fridge capacity reference.

Cubic Feet for Moving, Storage & Shipping

Removal firms quote by volume, self-storage is sold by floor area with a fixed ceiling, and freight carriers bill by whichever is greater, the weight or the space consumed. All three come back to cubic feet. Expand each group below for the standard figures.

Whichever of the three you are pricing, build the estimate from an inventory rather than a guess. Measure the largest items individually, a sofa, a mattress, a wardrobe, add the boxed total from the group above, then add about ten percent for the air gaps that any real load contains.

Cubic Feet to Weight

Cubic feet on their own tell you nothing about weight. Volume describes how much space something occupies; weight depends on the density of whatever fills that space, and densities vary enormously, a cubic foot of concrete weighs ten times as much as a cubic foot of bark mulch. To convert cubic feet to pounds you multiply the volume by the material's density in pounds per cubic foot, so the table below is the missing number in that calculation.

Following one row through: dry soil at 75 lb/ft³ means a 32 ft³ raised bed holds 2,400 pounds of material, or about 1.2 US tons, comfortably beyond what a car boot will take, and the reason garden centres deliver by the pallet. The same 32 ft³ in bark mulch weighs only 480 pounds, which one small trailer handles easily.

Three factors move these figures in practice. Moisture is the largest: soil, sand and gravel all gain weight after rain, sometimes by twenty percent or more. Compaction is the second, since the same material weighs more per cubic foot once it has been tamped down. Particle size is the third, coarse aggregate traps more air than fine material, so it is lighter per unit of volume even though the stone itself is just as dense.

This matters most for load limits rather than for ordering. Trailer ratings, skip capacities, vehicle payloads and upper-floor loading are all governed by weight, so a volume figure has to be converted before you can check it against any of them. Convert a specific quantity with the volume-to-poundage converter, which carries densities for a wider list of materials than the table above.

Cubic Feet for Air, Rooms & HVAC

Heating, cooling and ventilation all work on the volume of air in a space rather than its floor area, which is why a room with a vaulted ceiling needs more capacity than a same-sized room with a flat one. A cubic feet of air calculation is simply the room volume: length × width × ceiling height.

Beyond HVAC, room volume in cubic feet turns up in several everyday calculations. Air purifiers are rated by the room size they can clear, dehumidifiers by the volume they can dry, and extractor fans by how many times an hour they replace the air in a kitchen or bathroom. In each case the manufacturer's rating assumes a volume, so comparing products against your actual cubic footage is more reliable than comparing them against floor area alone.

Rule-of-thumb figures like these are estimates for planning and product comparison. A proper heat-load assessment accounts for insulation values, air infiltration, window orientation and local climate, and is worth commissioning before specifying equipment for a whole property.

Work through a room-by-room figure, including the ceiling-height adjustment, on the heating and cooling load page.

Complete Cubic Feet Conversion Chart

Every unit a cubic foot is commonly converted into, in one place, including US quarts and CBM, the cubic-meter figure freight forwarders quote against, which most conversion tables leave out. Each row is a single volume expressed seven ways.

Taking the 1 ft³ row as the reference conversion, a single cubic foot equals 0.0370 cubic yards, 0.0283 cubic meters, 1,728 cubic inches, 7.4805 US gallons, 29.9221 US quarts and 28.3168 liters. Every other row is that row scaled, so the table extends to any volume: 200 ft³ is simply double the 100 row, and 7.5 ft³ is the 5 row plus half the 5 row.

Two cautions on the liquid columns. These are US liquid gallons and quarts, an imperial gallon is about twenty percent larger, so a cubic foot holds roughly 6.23 of those instead of 7.48. And the litre column follows the metric definition exactly, since one cubic meter is precisely 1,000 litres, which makes the metric side of this table exact rather than rounded.

For values between the rows, or to convert in the opposite direction from litres or gallons back to cubic feet, the two-way volume conversion tool takes any unit as input and returns all the others at once.

Real-World Examples

Three complete calculations, worked from the tape measure to the decision they inform. Each one shows a different unit problem: comparing two objects, converting a depth given in inches, and rounding a finished volume up to an orderable quantity.

The pattern across all three is the same: convert every measurement to feet, multiply, then translate the answer into whatever the supplier sells in, bags, yards or box counts. That final translation is the step most calculators skip, and it is where the volume figure turns into an actual order.

Glossary of Cubic Feet Terms

Short definitions for the units and terms used across this page, including the ones most often mixed up with each other.

Cubic foot (ft³, cu ft)

The base unit of volume in the imperial system, and the one this page calculates in. Written inconsistently across the trades: ft³ on drawings and spec sheets, cu ft or CF on delivery notes and invoices, and cuft in spreadsheet exports and product feeds, all four refer to the same unit. In speech and in verbal quotes you will more often hear cubic footage, which is the informal name for the same measurement rather than a separate unit.

Cubic yard (yd³)

A cube three feet along every edge, containing exactly 27 cubic feet. The standard unit for bulk deliveries of concrete, topsoil, sand and aggregate.

Cubic meter (m³)

The metric unit of volume: a cube one meter on each side, holding 35.315 cubic feet or exactly 1,000 liters.

CBM

Shorthand for cubic meter on freight and shipping paperwork. Carriers use it to compare the space a consignment occupies against its weight when pricing a shipment.

Cuboid / rectangular prism

A six-sided box shape with right angles at every corner. It is the shape the length × width × height formula describes, and it covers rooms, crates, slabs and trenches.

Volume vs. area

Area measures a flat surface in two dimensions and is counted in square feet; volume measures the space inside an object in three dimensions and is counted in cubic feet. Square feet describe a floor, cubic feet describe the room above it.

CFM

Cubic feet per minute, a rate rather than a quantity, used to specify airflow through fans, extractors and ventilation ducts.

Board foot

A separate timber-trade unit equal to 144 cubic inches, or one twelfth of a cubic foot. It measures sawn lumber volume and should not be confused with cubic feet.

Frequently Asked Questions

Eighteen questions grouped into four topics. Every answer opens with the direct response, so you can read the first line and move on.

Related Tools

Eighteen dedicated calculators, each built around one job that the general tool at the top of this page handles more broadly. Pick the one that matches what you are measuring for a shorter set of inputs and results built around it.

• Cubic Yards Converter

  Switch a volume between cubic feet and cubic yards and see the equivalent bag count for bagged products.

• Cubic Meters Converter

  Move between imperial and metric volume, with the CBM figure shipping documents ask for.

• Inches Volume Calculator

  Work in inches and fractional inches without converting anything by hand first.

• Gallons Capacity Calculator

  Turn a tank or container volume into US gallons and liters for liquid capacity.

• Area to Volume Calculator

  Start from a known square footage and a depth to reach the volume you need to order.

• Cylinder Volume Calculator

  Round tanks, pipes and post holes from a diameter or radius plus a height.

• Soil Quantity Calculator

  Size a topsoil order for beds, borders and planters at the depth your planting needs.

• Mulch Coverage Calculator

  Find how many bags or yards of bark a bed takes at any spreading depth.

• Gravel Volume Calculator

  Estimate aggregate for driveways, paths and drainage runs including the base layers.

• Concrete Volume Calculator

  Slabs, footings and post holes converted into yards, bags or a ready-mix order.

• Fill Dirt Calculator

  Excavation and backfill quantities with an allowance for soil swell and compaction.

• Storage Unit Calculator

  Match a room-by-room inventory to the smallest self-storage unit that will hold it.

• Refrigerator Size Calculator

  Measure an interior cavity and compare the result against standard capacity classes.

• Shipping Volume Calculator

  Pallet, parcel and container cubic footage for freight quotes and customs paperwork.

• Volume to Weight Calculator

  Apply a material density to a volume to get the poundage for load and haulage limits.

• BTU Sizing Calculator

  Room-by-room heating and cooling estimates that account for ceiling height.

• Volume Formula Library

  Every common solid with its formula, a diagram and a fully worked calculation.

• Volume Unit Converter

  Enter any volume unit and read all the others back instantly, in either direction.