Work out cubic feet from length, width and height in any mix of feet, inches, yards, meters or centimeters. Then convert to cubic yards, cubic meters, liters and gallons, turn cubic feet into square feet when you know the height, or size a sauna heater from the room volume. Every result updates as you type.
How to calculate cubic feet
Cubic feet measures volume: how much space a box, room or load takes up. Measure the length, width and height, convert each one to feet, then multiply them.
Cubic feet = length (ft) x width (ft) x height (ft)
Inches to feet: divide by 12 (or multiply L x W x H in inches, then divide by 1,728)
Centimeters to feet: divide by 30.48 (or multiply in cm, then divide by 28,316.8)
Meters to feet: multiply by 3.28084
Worked example: a room 10 ft long, 8 ft wide and 7 ft high is 10 x 8 x 7 = 560 cubic feet. That equals 20.74 cubic yards, 15.86 cubic meters, about 15,857 liters or about 4,189 U.S. gallons. A box 24 in x 18 in x 16 in is 6,912 cubic inches, and 6,912 / 1,728 = 4 cubic feet.
Can you convert cubic feet to square feet?
Not on its own. Cubic feet measures volume (three dimensions) and square feet measures area (two dimensions), so there is no fixed conversion factor. You need the height or depth. Divide the cubic feet by the height in feet and you get the square feet of floor or surface it covers.
Square feet = cubic feet / height (ft)
Cubic feet = square feet x height (ft)
For example, 560 cubic feet spread at a 7 ft ceiling height covers 80 square feet. The same 560 cubic feet spread 4 inches deep (0.333 ft), like mulch or gravel, covers 1,680 square feet. That is why any tool that converts cubic feet to square feet without asking for a height cannot be right.
Volume conversion chart
| 1 cubic foot equals |
Value |
| Cubic inches |
1,728 |
| Cubic yards |
0.037037 (27 cu ft = 1 cu yd) |
| Cubic meters |
0.0283168 |
| Liters |
28.3168 |
| U.S. gallons (liquid) |
7.48052 |
Factors from the NIST Handbook 44 and NIST SP 811 unit conversion tables.
Sauna room volume and heater sizing
Traditional sauna heaters are sized by room volume, not floor area. A common rule of thumb is about 1 kW of heater for every 45 to 50 cubic feet of well insulated room. Glass doors and windows, and stone or tile walls, pull heat away, so manufacturers add effective volume for them and you should size up. A 6 x 5 x 7 ft room is 210 cubic feet, which works out to about 4.2 to 4.7 kW before any allowance for glass, so typically a 4.5 kW heater, or a step up with a large glass door. Always check the heater maker's room range before you buy, and have a licensed electrician size the circuit.
For a full recommendation with glass and build adjustments, use our sauna heater size calculator and the sauna breaker size calculator. To choose a room size first, try the sauna size calculator, then browse sauna heaters. Planning a cold plunge? The cold plunge size calculator and chiller sizing calculator work from tub volume in gallons.
Frequently asked questions
How do I calculate cubic feet?
Measure length, width and height, convert each to feet, and multiply them. If you measured in inches, multiply the three numbers and divide by 1,728. If you measured in centimeters, multiply and divide by 28,316.8.
How do I convert cubic feet to square feet?
Divide the cubic feet by the height or depth in feet. 300 cubic feet at a depth of 0.5 ft covers 600 square feet. Without a height or depth there is no single answer, because volume and area measure different things.
How many square feet is 1 cubic foot?
It depends on the depth. At 1 ft deep, 1 cubic foot covers 1 square foot. At 3 inches deep (0.25 ft) it covers 4 square feet, and at 2 inches deep it covers 6 square feet.
How many cubic feet are in a cubic yard?
27. A cubic yard is 3 ft x 3 ft x 3 ft. To turn cubic feet into cubic yards, divide by 27.
How many gallons are in a cubic foot?
About 7.48 U.S. liquid gallons, or 28.32 liters. A cold plunge holding 100 gallons of water contains about 13.4 cubic feet of water.
How many cubic feet is a room?
Multiply the floor length by the width by the ceiling height. A 12 x 12 ft bedroom with an 8 ft ceiling is 1,152 cubic feet. Room volume is what you use for heating, ventilation and sauna heater sizing.
Sources: NIST Handbook 44, Appendix C, and NIST Special Publication 811, Guide for the Use of the International System of Units. Sauna sizing is a planning rule of thumb; follow the heater manufacturer's specification. Prepared by Logan McClure, Restore Suite.
