To find cubic feet, multiply length × width × height, all in feet. If you measured in inches, multiply the three numbers and divide by 1,728. For a cylinder use π × radius² × height. One cubic foot equals 7.48 US gallons, 28.32 liters and 1/27 of a cubic yard.
Use it for a box, room, tank, pipe, pond, ball or cone. You need the shape and its dimensions in any one unit (inches, feet, yards, centimeters or meters); it converts the result to cubic yards, cubic meters, liters and gallons using NIST's exact definitions.
How to use this calculator
- Pick the shape: box or room, cylinder, sphere or cone.
- Choose the unit you measured in — inches, feet, yards, centimeters or meters. All dimensions use the same unit.
- Enter the dimensions. Cylinders and cones take the diameter (straight across) and height; a sphere takes the diameter.
- Set the quantity if you have several identical items, like boxes or bags.
- Read the volume in cubic feet, with cubic yards, cubic meters, liters and gallons below.
How it's calculated
The shape formulas are the standard ones in OpenStax Prealgebra 2e §9.6. Here l, w and h are length, width and height, r is the radius (half the diameter) and π ≈ 3.14159:
- Box:
V = l × w × h - Cylinder:
V = π × r² × h - Sphere:
V = 4/3 × π × r³ - Cone:
V = 1/3 × π × r² × h
Dimensions are converted to meters first (1 in = 0.0254 m and 1 ft = 0.3048 m exactly, per NIST), the volume is computed, and the result is divided by 0.028316846592 m³ — the exact size of one cubic foot. That avoids rounding errors when you mix metric and US units.
Worked examples
A room: 12 × 10 ft with an 8 ft ceiling
12 × 10 × 8 = 960 ft³, or 35.6 yd³ and 27.18 m³.
A shipping box measured in inches: 24 × 18 × 16 in
24 × 18 × 16 = 6,912 in³. Divide by 1,728: 4 ft³.
A round water tank: 4 ft across, 5 ft tall
Radius 2 ft: π × 2² × 5 = 62.83 ft³. That holds 470 US gallons, and the water would weigh about 3,920 lb — see the weight per gallon calculator.
A raised garden bed: 8 × 4 ft, 1 ft deep
8 × 4 × 1 = 32 ft³ of soil. If you're buying by the cubic yard: 32 ÷ 27 = 1.19 yd³.
A concrete slab: 10 × 10 ft, 4 in thick
Convert the thickness to feet first: 4 ÷ 12 = 0.333 ft. Then 10 × 10 × 0.333 = 33.33 ft³, or 1.23 yd³. Order a little extra to allow for an uneven base and spillage; the exact margin depends on your site and supplier.
Conversion tables
What one cubic foot equals in other volume units, from NIST's exact definitions (US gallon = 231 in³; UK gallon = 4.546 09 L):
| 1 cubic foot equals | Value |
|---|---|
| in³ | 1,728 |
| yd³ | 0.037037037 |
| m³ | 0.028316847 |
| L | 28.316846592 |
| US gal | 7.480519481 |
| UK gal | 6.228835459 |
Common volumes in gallons, liters and cubic yards — 27 ft³ is exactly one cubic yard:
| Cubic feet | US gallons | Liters | Cubic yards |
|---|---|---|---|
| 1 ft³ | 7.48 | 28.3 | 0.037 |
| 2 ft³ | 14.96 | 56.6 | 0.074 |
| 5 ft³ | 37.4 | 141.6 | 0.185 |
| 10 ft³ | 74.81 | 283.2 | 0.37 |
| 27 ft³ | 201.97 | 764.6 | 1 |
| 50 ft³ | 374.03 | 1,415.8 | 1.852 |
| 100 ft³ | 748.05 | 2,831.7 | 3.704 |
Converting cubic feet to pounds
Cubic feet measure volume, pounds measure weight, so you need the material's density: pounds = cubic feet × lb per ft³. Water uses NIST's 8.34 lb per gallon at 60 °F; soils, sand and gravel use the midpoint of US Army FM 5-434 loose weights, as in the cubic yard calculator. Real loads vary with moisture and compaction, so treat these as estimates:
| Material | lb per ft³ | 10 ft³ | 100 ft³ |
|---|---|---|---|
| Water (60 °F) | 62.4 | 624 lb | 6,239 lb |
| Topsoil or fill dirt, dry | 75.9 | 759 lb | 7,593 lb |
| Topsoil or fill dirt, wet | 111.1 | 1,111 lb | 11,111 lb |
| Pea gravel or river rock | 105.6 | 1,056 lb | 10,556 lb |
| Crusher run, loose | 97 | 970 lb | 9,700 lb |
| Crusher run, compacted | 142.6 | 1,426 lb | 14,259 lb |
| Sand, dry | 101.9 | 1,019 lb | 10,185 lb |
| Sand, wet | 109.3 | 1,093 lb | 10,926 lb |
| Mulch or wood chips | 13.3 | 133 lb | 1,326 lb |
| Concrete (fresh) | 147.5 | 1,475 lb | 14,750 lb |
Pond volume
Pick box for a rectangular pond or cylinder for a round one, and enter the average depth — most ponds have sloped sides and shelves, so the deepest point overstates the volume. Gallons = cubic feet × 7.4805.
- 10 × 6 ft, 2 ft average depth: 120 ft³ = 898 US gallons.
- Round, 8 ft across, 1.5 ft average depth: 75.4 ft³ = 564 US gallons.
Pipe and tube volume
A pipe is a cylinder: choose cylinder, enter the inside diameter and the length in the same unit (or inches for both and read cubic feet). Gallons per foot of pipe by inside diameter:
| Inside diameter | US gal per ft | ft³ per ft | Gallons in 100 ft |
|---|---|---|---|
| 0.5 in | 0.0102 | 0.0014 | 1 |
| 0.75 in | 0.0229 | 0.0031 | 2.3 |
| 1 in | 0.0408 | 0.0055 | 4.1 |
| 1.5 in | 0.0918 | 0.0123 | 9.2 |
| 2 in | 0.1632 | 0.0218 | 16.3 |
| 3 in | 0.3672 | 0.0491 | 36.7 |
| 4 in | 0.6528 | 0.0873 | 65.3 |
| 6 in | 1.4688 | 0.1963 | 146.9 |
| 8 in | 2.6112 | 0.3491 | 261.1 |
| 12 in | 5.8752 | 0.7854 | 587.5 |
Nominal pipe sizes aren't the inside diameter — measure the bore or check the manufacturer's spec for your pipe schedule.
Box sizes measured in inches
Cubic feet for a few common box sizes, using inside dimensions (inches multiplied, then ÷ 1,728):
| Box (inches) | Cubic inches | Cubic feet |
|---|---|---|
| 12 × 12 × 12 | 1,728 | 1 |
| 16 × 12 × 12 | 2,304 | 1.33 |
| 18 × 18 × 16 | 5,184 | 3 |
| 18 × 18 × 24 | 7,776 | 4.5 |
| 24 × 18 × 18 | 7,776 | 4.5 |
| 24 × 24 × 24 | 13,824 | 8 |
Common mistakes
- Mixing units. 10 ft × 8 ft × 6 in is not 480 ft³ — convert the 6 in to 0.5 ft first (answer: 40 ft³). The calculator avoids this by using one unit for all dimensions.
- Dividing inches by 12 instead of 1,728. A cubic foot is 12 × 12 × 12 cubic inches, so dividing by 12 or 144 gives a wrong answer.
- Using diameter as radius. Doubling the radius makes a cylinder four times too big. Enter the diameter here; the calculator halves it.
- Outside vs inside dimensions. For how much a box, tank or truck holds, measure the inside. For how much space it takes up, measure the outside.
- Confusing cubic feet and cubic yards. A cubic yard is 27 times bigger.
Cubic feet vs square feet
Square feet measure a flat area — length × width — and are what you use for flooring, paint or a lawn. Cubic feet add a third dimension, depth or height, and measure how much space something fills or holds. You can't convert square feet to cubic feet without knowing that third dimension: 100 ft² of floor with a 6 in (0.5 ft) layer of gravel is 50 ft³, but the same area at 3 in deep is only 25 ft³.
How to measure for an accurate result
- Use a tape measure rather than pacing or estimating, and measure each dimension at its longest straight line.
- For a room, measure wall to wall at floor level and floor to ceiling. Sloped or vaulted ceilings are best split into a box plus a separate shape.
- For a round container, measure straight across the widest point for the diameter. If you can only wrap a tape around it, divide the circumference by π to get the diameter.
- Round each measurement to the nearest quarter inch or centimeter; small errors multiply across three dimensions.
- Write down the unit with each number so you don't mix inches and feet.
Irregular shapes
Break an irregular space into boxes and cylinders, calculate each and add them. An L-shaped room is two rectangles. A tapered hole can be approximated by averaging the top and bottom sizes. For a ball or dome use the sphere setting — a 9-inch ball is 0.221 ft³ — and halve it for a hemisphere.
For soil, gravel or mulch sold by the yard, the cubic yard calculator adds tons and bags; for boards or trim, use the linear feet calculator; for bin and bag capacities, the trash bag size converter; and for pricing a remodel, the renovation cost calculator.
Frequently asked questions
How do you calculate cubic feet?
For a box or room, multiply length × width × height in feet. A 4 × 3 × 2 ft box is 24 ft³. If you measured in inches, multiply the three inch measurements and divide by 1,728 (12 × 12 × 12) — dividing by 12 is a common mistake. A 24 × 18 × 16 in box is 6,912 in³ ÷ 1,728 = 4 ft³.
How many gallons are in a cubic foot?
7.4805 US gallons (exactly 1,728 ÷ 231), 6.2288 UK gallons or 28.3168 liters. Going the other way, one US gallon is 0.13368 ft³. A UK gallon is about 20% larger than a US gallon, so check which one a spec uses.
How do I convert cubic feet to cubic yards?
Divide by 27, because a cubic yard is 3 × 3 × 3 = 27 ft³. A raised bed 8 × 4 × 1 ft holds 32 ft³, which is 1.19 yd³.
How many cubic feet in a cubic meter?
35.3147 ft³. One cubic foot is 0.028317 m³, because a foot is exactly 0.3048 m.
How do you find the cubic feet of a cylinder?
Volume = π × radius² × height. A cylinder 2 ft across and 3 ft tall holds 9.425 ft³.
How much does a cubic foot of water weigh?
About 62.4 lb: 7.481 gallons × 8.34 lb per gallon at 60 °F.
How do you convert cubic feet to pounds?
Multiply cubic feet by the material's density in pounds per cubic foot. Water is about 62.4 lb/ft³, so 10 cu ft of water weighs 624 lb. Dry dirt is roughly 76 lb/ft³ and dry gravel 106 lb/ft³ — see the cu ft to lbs table.
How do I calculate pond volume?
Multiply length × width × average depth in feet for cubic feet, then × 7.48 for gallons. A 10 × 6 ft pond averaging 2 ft deep is 120 ft³ = 898 gallons. For a round pond use the cylinder setting with the diameter and average depth.
How do you calculate the volume of a pipe or tube?
Use the cylinder setting: the inside diameter and the length. Volume = π × (ID ÷ 2)² × length. A 4-inch pipe holds 0.653 US gallons per foot, so 100 ft holds 65.3 gallons.
What is CFT?
CFT is a common abbreviation for cubic feet (ft³), a unit of volume equal to a cube 1 ft on each side. You'll see it on things like storage units, shipping quotes and bags of soil or mulch.
Sources & method
- NIST Handbook 44 (2026), Appendix C — units of volume (1 ft³ = 1,728 in³ = 28.316 846 592 L)
- NIST SP 811, Appendix B.8 — conversion factors (inch = 0.0254 m exactly)
- UK Weights and Measures Act 1985, Schedule 1 — UK gallon = 4.54609 L
- OpenStax Prealgebra 2e, §9.6 — volume of rectangular solids, cylinders, spheres and cones
- US Army FM 5-434 Earthmoving Operations, Table 1-2 — loose weights of soil, sand and gravel
- NIST Chemistry WebBook SRD 69 — density of water (8.34 lb/US gal at 60 °F)
Results are estimates for general information. Found an error? It helps everyone — see our methodology.