Cu Feet Calculator
Cu feet is the number that decides how much a room holds, how much a tank stores, and how much space a load takes up, yet the measuring is usually the easy part and the shape is what trips people up. A box multiplies straight across, a cylinder needs pi and a radius, and a sphere needs the radius cubed, and using the box formula for all three gives answers that are quietly wrong.
This calculator keeps it deliberately simple: every measurement is entered in feet, you pick the shape, and it returns the volume in cubic feet plus the five conversions people ask for next, cubic inches, cubic yards, US gallons, liters, and cubic meters. No unit settings to set wrong, and no shape buried in a long list.
Measurements are in feet only. If your tape reads in inches, divide each measurement by 12 before entering it, or use a multi-unit tool instead. Results assume the full geometric shape; a tank filled to the brim and a tank filled to a working level are different numbers.
Quick Answer
Key takeaways
- Shape first, numbers second: a box, a cylinder, and a sphere with similar measurements hold very different volumes, and the wrong formula is a bigger error than a sloppy measurement.
- Every input is in feet. There is no unit selector to leave on the wrong setting, which removes the most common cause of wildly wrong volume answers.
- Cylinder and sphere modes ask for the radius. If you measured across the widest point, you have the diameter, so halve it first.
- One result, six units: cubic feet leads, and cubic inches, cubic yards, gallons, liters, and cubic meters follow from fixed conversion factors.
- Quick Answer
- How to use the cu feet calculator
- The three formulas this calculator uses
- Worked examples for all three shapes
- Feet only, on purpose: when that helps and when it does not
- What most cubic feet tools get wrong
- Reading the six outputs without a second tool
- Frequently Asked Questions
- Add This Calculator to Your Website
- References
How to use the cu feet calculator
Start with the shape selector, because it changes which fields appear. A rectangular box asks for length, width, and height. A cylinder asks for the radius of the round end and the height. A sphere asks for the radius alone. Enter the measurements in feet, press Calculate Volume, and read the cubic feet figure first; the five conversions underneath it are the same volume expressed other ways, not separate calculations.
Two measuring decisions matter more than decimal places. For capacity, meaning how much a container holds, measure the inside. For shipping and storage planning, meaning how much room something takes up, measure the outside at its longest points. Mixing the two is how a crate that should fit ends up an inch too wide. If your project is a plain box and nothing else, the dedicated box volume calculator covers that single job in more depth.
The three formulas this calculator uses
Each shape has exactly one formula here, and the calculator applies the one matching your selection. Nothing else is hidden in the tool: there is no cone mode, no pyramid mode, and no allowance or waste factor added on top.
| Shape | You measure | Formula | Typical job |
|---|---|---|---|
| Rectangular box | Length, width, height | V = L x W x H | Rooms, crates, storage units, raised beds |
| Cylinder | Radius, height | V = pi r² h | Tanks, silos, pipes, round pools |
| Sphere | Radius only | V = (4/3) pi r³ | Spherical tanks, balls, domes treated as full spheres |
The radius is where cylinder and sphere calculations usually go wrong. Both formulas need half the width across the shape, not the full width. Entering a 10 ft diameter as a 10 ft radius does not double the answer; it multiplies a cylinder result by four and a sphere result by eight, because the radius is squared in one formula and cubed in the other. That single slip explains most of the impossible tank capacities people bring to support forums.
Worked examples for all three shapes
The box below is the pre-filled example, and the cylinder and sphere use the pre-filled values in their own modes, so you can reproduce every row exactly.
| Shape and inputs | Cubic feet | Cubic yards | US gallons | Liters |
|---|---|---|---|---|
| Box, 10 x 8 x 6 ft | 480.00 ft³ | 17.78 yd³ | 3590.65 gal | 13592.06 L |
| Cylinder, radius 5 ft, height 10 ft | 785.40 ft³ | 29.09 yd³ | 5875.19 gal | 22239.96 L |
| Sphere, radius 5 ft | 523.60 ft³ | 19.39 yd³ | 3916.79 gal | 14826.64 L |
Read the cylinder row carefully if you size tanks. A 5 ft radius means a 10 ft wide tank, and at 10 ft tall it holds 5875.19 gallons by geometry. Manufacturers rate real tanks below the brim-full figure to leave headspace, so a nameplate capacity smaller than the calculator result is normal, not a sign the math is off. For a ball or spherical tank on its own, the ball volume calculator works the same sphere formula with more ball-specific examples.
Feet only, on purpose: when that helps and when it does not
This tool takes feet and only feet. That is a real limitation and a real strength, and which one it is depends on what is on your tape measure. US construction, moving, and storage work is still specified in feet: room sizes, truck capacities, storage unit sizes, and tank drawings all arrive in feet, so a feet-only tool removes the unit-mismatch errors that plague multi-unit calculators.
Feet only works well when
- Your drawings, listings, or tape already read in feet
- You want a sphere volume, which most cubic feet tools skip
- You need gallons or liters from a feet measurement without a second converter
- You are checking someone else’s figure and want the fewest possible settings involved
Use the multi-unit tool when
- Your measurements are in inches, yards, meters, or centimeters
- You know a floor area in square feet and a depth, but not length and width
- You also need the surface area of the box or cylinder
- You want each conversion step written out under the result
The second list is exactly what the companion cubic footage calculator does: it accepts five input units, adds a floor area mode, and shows surface area and step-by-step working. The two tools overlap on plain boxes in feet, and diverge everywhere else, so pick by your measurements rather than by habit.
What most cubic feet tools get wrong
The top-ranking cubic feet tools reviewed for this page are mostly box calculators with a conversion table attached. Three gaps kept appearing.
Gap 1: no sphere. Spherical tanks are standard equipment in propane, chemical, and water storage, yet almost no feet-first tool offers a sphere mode, so users end up on a generic multi-shape page with twelve shapes and per-field unit menus. Here the sphere sits next to the box, one radius, one answer.
Gap 2: radius and diameter used loosely. Several tools label a field just “width” on a cylinder and leave you to guess whether the formula expects a radius. Guessing wrong costs a factor of four. The fields here say radius, the tooltips say how to get it from a diameter, and the worked examples show a stated radius so the convention is checkable.
Gap 3: conversions promised, inputs assumed. Some pages describe automatic conversion from inches or meters while the actual form accepts only feet, which is how a 36 inch side becomes a 36 ft side and a result lands 1,728 times too large. This page states the feet-only rule in the intro, in the card, and again under the results, and if you do have inches, the honest route is to divide by 12 first or use the multi-unit companion tool linked above. For pours and slabs specifically, the concrete volume calculator takes the box volume further into yards and bag counts.
Reading the six outputs without a second tool
Every conversion in the results comes from one cubic foot, so the whole panel can be sanity-checked against these fixed factors, which follow the definitions in NIST guidance on unit conversion factors.
The gallons figure deserves one caution: it is the US liquid gallon. An imperial gallon is larger, so a UK specification converted at 7.48052 gallons per cubic foot will understate the imperial count. The cubic meters line is shown to four decimal places because small volumes vanish at two: a 1 ft³ block is 0.0283 m³, and rounding that to 0.03 would throw away about 6 percent of the value.
Frequently Asked Questions
Multiply the length, width, and height, all in feet: V = L x W x H. A box of 10 ft by 8 ft by 6 ft is 10 x 8 x 6 = 480.00 ft³. Order does not matter, but every measurement must be in feet before you multiply.
None. Cu feet, cu ft, ft³, and CFT are all abbreviations for the same unit, the volume of a cube measuring one foot on each side. Freight documents often use CFT, and US listings usually write cubic feet or ft³.
Halve it. The radius is half the distance straight across the shape, so a tank that measures 10 ft across has a radius of 5 ft. Entering the full diameter as the radius multiplies a cylinder result by four and a sphere result by eight, which is the single most common error with round shapes.
No. Every input is in feet, by design, so there is no unit setting to get wrong. If your measurements are in inches, divide each one by 12 first. If they are in meters, multiply by 3.28084, or use the cubic footage calculator, which accepts feet, inches, yards, meters, and centimeters directly.
7.48052 US liquid gallons. The figure follows from the US gallon being defined as 231 cubic inches and a cubic foot holding 1,728 cubic inches: 1728 / 231 = 7.48052. Note that this is the US gallon; an imperial gallon is about 20 percent larger.
27. A cubic yard is a cube 3 ft on each side, and 3 x 3 x 3 = 27. The calculator divides your cubic feet by 27 for the cubic yards line, which is the unit bulk soil, mulch, and concrete are usually sold by.
No. It covers three shapes only: a rectangular box, a cylinder, and a sphere. For an irregular space, the practical method is to split it into box and cylinder sections, calculate each section here, and add the results together.
Add This Calculator to Your Website
References
- National Institute of Standards and Technology, “Guide to the SI, Appendix B: Conversion Factors” – the authoritative factors behind the foot, liter, and cubic meter conversions used in the results. NIST: Guide to the SI, Appendix B. Accessed October 2026.
- National Institute of Standards and Technology, “SI Units: Length” – definitions of the foot and meter and their exact relationship. NIST: SI Units, Length. Accessed October 2026.
- LibreTexts, “SI (Metric) Units” – an open textbook summary of volume units and how cubic measures relate to the liter. LibreTexts: SI (Metric) Units. Accessed October 2026.
- Stewart, “Volume and Surface Area” lecture notes – worked derivations of the box, cylinder, and sphere volume formulas used here. Stewart: Volume and Surface Area (PDF). Accessed October 2026.
- National Institute of Standards and Technology, “Guide for the Use of the International System of Units (SI)” (Special Publication 811, full text) – rounding and conversion practice for reporting converted values. NIST: SP 811 full text (PDF). Accessed October 2026.