Cubic Feet Calculator

How to calculate cubic feet

Cubic feet is a measure of volume: for a box or a room, it's length × width × height, with all three measured in feet. A box that is 2 ft × 1.5 ft × 1 ft is 2 × 1.5 × 1 = 3 cubic feet. Enter your dimensions above, pick each dimension's unit, and the total updates live — no Calculate button.

The formula changes with the shape: a cylinder (a drum, a pipe, a round tank) is π × radius² × height, and an area × height mode covers slabs, mulch beds or soil where you already know the square footage and just need a depth multiplied in. All three modes are built into the calculator above.

The #1 mistake: mixing units before you multiply

The most common error in a cubic-foot calculation is multiplying raw numbers measured in different units. A box that is 24 in × 18 in × 12 in is not 24 × 18 × 12 = 5,184 — that's 5,184 cubic inches, not cubic feet. To get cubic feet, either convert each side to feet first (24 in ÷ 12 = 2 ft, 18 in ÷ 12 = 1.5 ft, 12 in ÷ 12 = 1 ft, then 2 × 1.5 × 1 = 3 cu ft) or multiply in inches and divide the result by 1,728 (5,184 ÷ 1,728 = 3 cu ft, since 1,728 = 12³).

This gets harder when a room is measured in feet but a depth is measured in inches — for example, sizing mulch for a bed that's 50 sq ft at a 6-inch depth. 6 inches is 0.5 ft, so the volume is 50 × 0.5 = 25 cu ft, not 50 × 6 = 300. The calculator above lets every dimension carry its own unit and converts each one to feet internally before multiplying, so this trap can't happen.

Cubic feet vs. cubic yards

A cubic yard is 27 cubic feet (3 ft × 3 ft × 3 ft), and it's the unit soil, mulch, gravel and ready-mix concrete are usually priced and delivered in — a supplier will often quote "$45 a yard" rather than a price per cubic foot. To convert, divide cubic feet by 27: a 12 ft × 10 ft × 8 ft room is 960 cu ft, which is 960 ÷ 27 ≈ 35.56 cu yd. The calculator shows both figures side by side so you can order in whichever unit your supplier uses.

Exact conversion factors

All conversions below use exact figures from NIST Handbook 44 and the international foot definition (1 ft = 0.3048 m exactly; 1 US liquid gallon = 231 cubic inches exactly) — not the rounded factors some calculators publish.

1 cu ft = 1,728 cu in (12³, exact) · 1 cu ft = 1 ÷ 27 cu yd (27 cu ft = 1 cu yd, exact) · 1 cu ft = 0.028316846592 m³ (0.3048³, exact) · 1 cu ft = 28.316846592 L (exact) · 1 cu ft = 7.480519... US gal (1,728 ÷ 231, exact repeating decimal) · 1 cu ft = 29.922078... US qt (4 × the gallon factor).

Moving boxes and storage units

Movers and self-storage companies size jobs in total cubic feet: a small 5×5 storage unit is roughly 200 cu ft (at 8 ft ceilings), a 10×10 is about 800 cu ft, and a 10×20 is about 1,600 cu ft. To estimate your own load, add one row per box size and quantity — ten identical 24 in × 18 in × 12 in boxes (3 cu ft each) come to 30 cu ft total — and the calculator's running total tells you which unit size fits, or roughly how many cubic feet a moving truck quote should cover.

Appliance and container capacity

Refrigerator, freezer and cooler capacity is usually advertised in cubic feet of interior space — a typical single-door fridge is around 18–20 cu ft, a compact dorm fridge around 3–5 cu ft. To check a listed capacity or size a replacement, measure the usable interior length, width and height (in inches is fine — the calculator converts) and compare the result to the spec sheet.

Soil, mulch and material by volume

For a flower bed, raised garden or mulch job, volume is area × depth: a 10 ft × 8 ft bed at a 3-inch (0.25 ft) depth needs 10 × 8 × 0.25 = 20 cu ft of material, which most bagged mulch (usually 2 cu ft per bag) sells in — that's 10 bags. Use the "Area × height" mode above, enter the bed's area and the depth, and add a cost per cubic foot or cubic yard if you know the delivered price.