Square Feet to Cubic Feet Calculator
Results update as you type, there is no submit button.
Enter an area in square feet and a depth in either inches or feet, and this calculator returns the volume in cubic feet, cubic yards and cubic meters at once. It's the tool for when you already know a floor or bed's footprint and only need the third dimension added on top, flooring, insulation, landscaping and slab work all start from exactly this calculation.
Area Measures a Surface; Volume Measures What Sits on It
Area to volume
Volume (ft³) = Area (sq ft) × Depth (ft)
Depth is the third dimension that turns a flat area into a filled space.
Square feet and cubic feet answer different questions. A 400 sq ft room tells you how much floor there is; it doesn't tell you how much air, insulation or concrete fills the space above that floor until you add a height or depth. That third number, depth for material spread over a surface, height for a room's air volume, is the entire difference between the two units, and multiplying the area by it in feet is the entire calculation.
Where the Depth Mistake Happens
Almost every error on this kind of calculation comes from the same place: material depths are quoted in inches, areas are quoted in square feet, and multiplying the two directly, without converting the depth to feet first, overstates the result by 12 times. A 400 sq ft area covered 3 inches deep needs 100 ft³ of material (400 × 0.25), not 1,200 ft³ (400 × 3). The chart below removes that arithmetic: find your depth in the left column, read the feet-equivalent multiplier next to it, and multiply your square footage by that number instead of the raw inch figure.
| Depth (inches) | Depth (feet) | ft³ per 100 sq ft |
|---|---|---|
| 1 in | 0.0833 ft | 8.33 ft³ |
| 2 in | 0.1667 ft | 16.67 ft³ |
| 3 in | 0.2500 ft | 25.00 ft³ |
| 4 in | 0.3333 ft | 33.33 ft³ |
| 6 in | 0.5000 ft | 50.00 ft³ |
| 8 in | 0.6667 ft | 66.67 ft³ |
| 12 in | 1.0000 ft | 100.00 ft³ |
This is the same chart used on the homepage calculator, kept identical here so a figure you check on either page always agrees.
Three Everyday Uses
Flooring and underlayment: self-leveling compound and some underlayment products are ordered by volume once you know the area and the pour thickness, the same area-times-depth math as everything else on this page, just with a much thinner depth figure.
Insulation: attic and wall insulation coverage is usually quoted in square feet at a specific installed depth, but converting to cubic feet lets you compare products rated to different depths on equal footing, or check that a delivered quantity actually matches the coverage claimed on the bag.
Landscaping: soil, mulch and gravel orders are exactly this calculation with a garden bed standing in for the "area." The soil calculator and concrete calculator both build on the same area-times-depth core shown here, adding material-specific outputs, bag counts, weight, waste factors, on top of it.
Working With Irregular Areas
Real spaces are rarely perfect rectangles, which means the "area" half of this calculation often needs its own arithmetic before you ever reach the depth multiplication. An L-shaped room or bed splits into two rectangles, measure and calculate each section's area separately, then add the two together before entering the combined total into the calculator above. The same divide-and-sum approach extends to any number of sections: a U-shaped area splits into three, a stepped or terraced area into as many sections as it has distinct levels.
The only rule that matters when splitting an irregular shape this way is that the sections must not overlap, if you find yourself counting the same square foot of floor or bed twice, move the dividing line rather than trying to adjust the final numbers to compensate. For a shape with a genuinely curved edge rather than straight irregular sides, a circular planter bed, say, treating it as a rectangle will overstate or understate the area depending on which way you round the boundary; the cylinder and other formulas on the volume formula reference page handle true curves properly where a rectangle approximation isn't precise enough.
From Blueprint Area to Ordered Volume
Architectural drawings and property listings almost always give area, not volume, which makes this calculator the bridge between a document you already have and a material order you're about to place. A floor plan might list a room at 180 sq ft; a landscaping plan might show a bed at 45 sq ft; a roofing estimate works from the building's footprint in square feet. None of those documents typically state a depth or height directly, because that number depends on what you're doing with the space, not on the space itself, an 8 ft ceiling and a 12 ft ceiling produce very different air volumes from the identical 180 sq ft floor plan, and a 3-inch mulch layer and a 6-inch mulch layer produce very different material orders from the identical 45 sq ft bed.
That's the reason this calculator asks for area and depth as two separate inputs rather than trying to guess one from the other: the area comes from wherever you're sourcing the plan or listing, and the depth is a decision you make based on what the project actually needs, which this page's earlier sections and chart are built to help you land on with confidence rather than guesswork.
A Quick Sanity Check
Because depth is almost always the smallest of the three numbers involved, the resulting cubic-feet figure should be a fairly modest multiple of the area you started with, a depth under a foot means the volume in cubic feet will be smaller than the area in square feet, not dramatically larger. If a result comes out many times bigger than the area, the most likely explanation is a depth that was entered in inches but not converted to feet before multiplying, the single most common mistake this calculator exists to prevent.
Area From a Property Listing Isn't Always Reliable
Square footage pulled from a real estate listing or an old survey sometimes measures something slightly different than what you're calculating a depth against, a listing's "square footage" might include or exclude a garage, a covered porch, or interior wall thickness depending on the standard the original measurement used. For anything where the material order depends on getting the area exactly right, a fresh measurement of the actual space you're filling or covering is worth the extra ten minutes rather than trusting a secondhand figure that may not mean quite what it appears to.
Frequently Asked Questions
What's the difference between area and volume in plain terms?
Area is how much floor a shape covers, measured in two dimensions; volume is how much space fills up above that floor once you add a height or depth, measured in three. A blueprint gives you area, a delivery order needs volume.
How much insulation do I need for a given attic floor area?
Multiply the attic's square footage by the insulation depth (in feet) to get cubic feet, then check that figure against the R-value chart for the insulation type you're using, most batt and blown-in products list coverage in square feet per bag at a specific depth rather than in cubic feet directly.
Why does a 3-inch depth mistake matter so much on a large area?
Because the error scales with area, get the depth wrong by a factor of 12 (confusing inches for feet, for instance) on a 500 sq ft space and the volume error is enormous, not a rounding blip. Always convert depth to feet before multiplying, never after.
Can I use this calculator for flooring underlayment or a concrete slab?
Yes, flooring underlayment, self-leveling compound and concrete slabs are all area-times-depth calculations. For concrete specifically, the dedicated concrete calculator adds bag counts and a waste-factor option on top of the same math. Convert a spec sheet's thickness from inches to feet first, since this calculator's depth field expects feet.