Cubic Inches to Cubic Feet Calculator
Type into either field, the other converts instantly.
Or: three inch measurements, fractions welcome
Enter fractional inches as "34 1/2" or "34-1/2", no need to convert to a decimal first.
The top calculator converts a cubic-inch or cubic-foot figure you already have. The one below it takes three linear inch measurements instead, length, width and height, including fractional readings like 34½ written exactly as you'd say them out loud, with no decimal conversion required first.
The 1,728 Divisor
Cubic inches to cubic feet
Cubic Feet = Cubic Inches ÷ 1,728
1,728 is 12³, twelve inches per foot, cubed across three dimensions.
A single foot holds 12 inches, so a cube one foot on every side holds 12 × 12 × 12 inch-cubes stacked inside it, 1,728 of them. That single number is the entire relationship between the two units: multiply three inch measurements together to get cubic inches, then divide by 1,728 to land in cubic feet, the unit most bulk-material and volume calculations on this site (starting with the homepage calculator) actually use.
Going the other direction is just as direct, multiply a cubic-feet figure by 1,728 to see it in cubic inches, which matters when you're comparing a small appliance cavity or shipping carton against a spec sheet that quotes inches rather than feet.
Why Interior and Appliance Measurements Use Inches
Feet are the natural unit for rooms and lots; inches are the natural unit for anything small enough that a foot-based reading would round away real precision. A refrigerator's interior cavity, a speaker enclosure, a drawer, a shipping carton, all of these are measured in inches because the difference between 17 and 18 inches of interior depth is significant, where the equivalent difference in feet (1.42 ft vs 1.5 ft) reads as barely worth noting. That's also why appliance capacity specs, packaging dimensions and speaker-box design plans are almost always written in inches even though the final published capacity figure, 18.5 cubic feet, say, comes out in cubic feet once the arithmetic is done.
Speaker enclosure design is a particularly exact use case: a sealed subwoofer box's internal volume has to land within a narrow range specified by the driver manufacturer, and that spec is almost always given in cubic feet even though every panel gets cut and measured in inches. Building the box to inch dimensions and converting the finished internal volume back to cubic feet with this page's divisor is the standard workflow, and it's exactly the same arithmetic a storage unit comparison or a packing-carton volume check uses.
Reading a Tape Measure in Fractions
Standard tape measures mark increments in sixteenths of an inch, not decimals, so a real-world measurement is far more likely to come out as "34 and 5/16" than "34.3125", even though those are the same length. This page's fractional-input field is built specifically so you never have to do that decimal conversion by hand before calculating a volume: type the reading exactly as the tape shows it, with a space before the fraction (34 5/16) or a hyphen (34-5/16), and the calculator handles the rest.
Common fractions and their decimal equivalents, if you ever need to check the conversion by hand: ⅛ = 0.125, ¼ = 0.25, ⅜ = 0.375, ½ = 0.5, ⅝ = 0.625, ¾ = 0.75, ⅞ = 0.875. Sixteenths split each of these in half again, 1/16 = 0.0625, 3/16 = 0.1875, and so on, which is precise enough for nearly any household or workshop measurement, but rarely worth typing out by hand when the fractional field above does it instantly.
Worked Example: A Shipping Carton
A carton measuring 20 in × 16 in × 14 in:
20 × 16 × 14 = 4,480 in³
4,480 ÷ 1,728 = 2.593 ft³
That figure, 2.593 ft³, is what a freight or parcel carrier's dimensional weight calculation actually uses, not the inch measurements the carton was built to. If you're pricing several cartons for a shipment, the shipping volume calculator runs the same conversion across length, width and height in either inches or centimeters and adds the cubic-meter figure international carriers ask for alongside it.
Board Feet: A Related but Different Unit
Lumber is measured in a unit that looks similar but isn't the same as anything on this page: the board foot, equal to 144 cubic inches, or a board one foot long, one foot wide and one inch thick. It's exactly a twelfth of a cubic foot, which is close enough to a cubic-inch-style unit that the two get confused, but the lumber trade's board foot is a fixed quantity independent of a board's actual shape, a 2×4 stud and a 1×6 plank of the same board-footage are priced the same per board foot even though their cross-sections are completely different. Don't substitute this page's cubic-inch or cubic-foot arithmetic for a lumber quote that's specifically priced in board feet; convert to board feet directly instead if that's the unit you're pricing against.
For anything else measured in inches that isn't lumber, furniture, containers, appliance cavities, packaging, the plain cubic-inch-to- cubic-foot conversion at the top of this page is the one that applies, and it's the same 1,728 divisor throughout regardless of what the object actually is.
A Quick Sanity Check
Because 1,728 is a large divisor, a cubic-feet result should always be a much smaller number than the cubic-inch figure it came from, typically two to three orders of magnitude smaller for anything household-sized. If your calculated cubic feet come out looking suspiciously close to the cubic inches you started with, the division likely didn't happen, or happened by the wrong number, re-run the arithmetic before trusting the figure for an order or a spec comparison.
Working Backward From a Target Volume
Sometimes the question runs in reverse: you know the cubic-foot or cubic-inch volume you need, a speaker box's specified internal volume, say, and need to find dimensions in inches that achieve it, rather than starting from measurements and calculating a resulting volume. There's no single answer here, since infinitely many length-width-height combinations multiply to the same volume; the usual approach is to fix two of the three dimensions based on some other constraint (available space, panel material dimensions on hand) and solve for the third by dividing the target volume by the product of the other two. Once you have a candidate set of three dimensions, running them forward through this page's calculator confirms they land on the target volume before you cut any material.
Frequently Asked Questions
Where does the 1,728 figure actually come from?
It's 12 cubed, 12 × 12 × 12, because a cubic foot is a box one foot on every side, and one foot is 12 inches, so there are 12 layers of 12-by-12 inch squares stacked 12 deep inside it.
Why are appliance and speaker-box measurements almost always in inches?
Interior cavities, refrigerator compartments, speaker enclosures, drawer interiors, are small enough that inches give a usefully precise reading, where feet would force awkward decimals for every measurement. A refrigerator's interior capacity spec, for instance, is built from inch measurements and only converted to cubic feet at the very last step.
How do I handle a measurement like 34 and a half inches without a calculator that takes fractions?
Convert the fraction to a decimal first (½ = 0.5, so 34½ becomes 34.5), or use the fractional-input field on this page, which accepts "34 1/2" directly and does that conversion for you. The same approach works for eighths and sixteenths, convert each fraction to its decimal equivalent before adding it to the whole-inch figure.
Is a cubic inch a standard unit for anything besides small enclosures?
It shows up in engine displacement (a "350 cubic inch" engine), some packaging specs, and anywhere else a volume is small enough that cubic feet would round awkwardly, but for most household and construction purposes, it's an intermediate step on the way to cubic feet rather than a final answer.