To calculate cubic feet for a rectangular space, multiply its length, width and height after converting all three measurements to feet. For example, a box measuring 4 feet long, 3 feet wide and 2 feet high has a volume of 4 × 3 × 2 = 24 cubic feet.
Cubic feet measure three-dimensional volume, not floor area. The correct formula depends on the object's shape: use length × width × height for a box or room, π × radius² × height for a cylinder, and ½ × base × triangle height × prism length for a triangular prism.
Convert every linear measurement to the same unit before multiplying. A result in cubic feet is written as ft³ or cu ft.
What Is a Cubic Foot?
A cubic foot is the volume of a cube whose length, width and height are each one foot. Because volume uses three dimensions, the unit is cubed: ft × ft × ft = ft³.
Cubic feet are commonly used for rooms, storage containers, appliances, shipping packages, soil, mulch, concrete, air volume and other three-dimensional spaces. The measurement describes capacity or occupied space; it does not describe weight or material density.
How to Calculate Cubic Feet Step by Step
Identify the shape
Decide whether the object is a rectangular box, room, cylinder, triangular prism or a combination of simpler shapes.
Measure the dimensions
Record the required length, width, height, radius, diameter or triangular dimensions. Use inside dimensions when calculating usable capacity.
Convert to feet
Divide inches by 12. Convert centimeters or meters before applying a cubic-foot formula, or calculate in metric units and convert the final volume.
Apply the shape formula
Multiply the converted dimensions according to the correct geometry. Keep extra digits until the final result, then round appropriately.
Example 1: Rectangular Box Measured in Feet
Suppose a storage box is 4 feet long, 3 feet wide and 2 feet high.
Cubic feet = 4 × 3 × 2
Cubic feet = 24 ft³
The box's theoretical rectangular volume is 24 cubic feet. Actual usable capacity may be lower if the walls, lid, wheel wells, shelves or internal components occupy space.
Example 2: Room Volume
A room is 12 feet long, 10 feet wide and 8 feet high.
Cubic feet = 12 × 10 × 8
Cubic feet = 960 ft³
The floor area is 12 × 10 = 120 square feet, while the room volume is 960 cubic feet. This distinction matters for air volume, ventilation and storage planning.
How to Calculate Cubic Feet from Inches
One foot contains 12 inches, so one cubic foot contains 12 × 12 × 12 = 1,728 cubic inches. You can either convert each dimension to feet first or multiply the dimensions in inches and divide the cubic-inch result by 1,728.
For a package measuring 48 inches × 30 inches × 24 inches:
Cubic inches = 48 × 30 × 24 = 34,560 in³
Cubic feet = 34,560 ÷ 1,728 = 20 ft³
How to Calculate Cubic Feet from Feet and Inches
Convert the inches portion of each mixed measurement to a fraction of a foot, then add it to the whole feet.
Suppose a cabinet measures 5 ft 6 in × 2 ft 3 in × 3 ft 4 in:
5 ft 6 in = 5 + 6 ÷ 12 = 5.5 ft
2 ft 3 in = 2 + 3 ÷ 12 = 2.25 ft
3 ft 4 in = 3 + 4 ÷ 12 = 3.3333… ft
Volume = 5.5 × 2.25 × 3.3333… = 41.25 ft³
Cubic Feet Formulas for Common Shapes
| Shape | Formula | Measurements required |
|---|---|---|
| Rectangular box or room | L × W × H | Length, width and height |
| Cube | Side³ | One side length |
| Cylinder | πr²h | Radius and height |
| Triangular prism | ½ × b × h × L | Triangle base, triangle height and prism length |
| Sphere | 4/3 × πr³ | Radius |
Every dimension in these formulas must be expressed in feet if you want the answer directly in cubic feet.
Example 3: Cylinder Volume in Cubic Feet
A cylindrical tank has a diameter of 4 feet and a height of 6 feet. The radius is half the diameter, so r = 2 feet.
Volume = π × 2² × 6
Volume = 24π ≈ 75.40 ft³
Use inside diameter and inside height when estimating internal capacity. For a dedicated breakdown, use the Cylinder Volume Calculator.
Example 4: Triangular Prism
A triangular prism has a triangle base of 4 feet, a triangle height of 3 feet and a prism length of 10 feet.
Triangle area = ½ × 4 × 3 = 6 ft²
Volume = 6 × 10 = 60 ft³
How to Calculate an Irregular Space
Break an irregular object into boxes, cylinders or other simple shapes. Calculate the cubic feet of each section, then add the volumes. If part of the object is an empty cutout, calculate that section and subtract it.
Use non-overlapping sections. Counting the same area in two component shapes will overstate the final volume.
Cubic Feet Conversion Table
| Starting volume | Equivalent | Operation |
|---|---|---|
| 1 cubic foot | 1,728 cubic inches | Multiply ft³ by 1,728 |
| 1 cubic foot | 1/27 cubic yard | Divide ft³ by 27 |
| 1 cubic foot | 0.028316846592 cubic meter | Multiply ft³ by 0.028316846592 |
| 1 cubic foot | 28.316846592 liters | Multiply ft³ by 28.316846592 |
| 1 cubic foot | About 7.48052 U.S. liquid gallons | Multiply ft³ by 7.48052 |
Use enough digits for the accuracy of your measurements, but do not imply more precision than the input dimensions support. Round the final result rather than shortening conversion factors before the calculation.
Cubic Feet vs Square Feet and Linear Feet
| Measurement | Dimensions | Typical formula | What it describes |
|---|---|---|---|
| Linear feet | One | Length | Distance |
| Square feet | Two | Length × width | Area |
| Cubic feet | Three | Length × width × height | Volume |
You cannot convert square feet to cubic feet without a third dimension. Multiply square footage by depth or height in feet: cubic feet = square feet × depth.
Common Cubic Feet Calculation Mistakes
- Multiplying feet by inches without converting them to the same unit.
- Using floor area alone and forgetting the height or depth.
- Dividing cubic inches by 12 instead of 1,728.
- Using diameter as the radius in a cylinder formula.
- Using outside measurements when the goal is internal usable capacity.
- Calculating an irregular object as one large box and including empty space.
- Confusing cubic feet with square feet, board feet, gallons or weight.
- Rounding converted dimensions before multiplying them.
- Adding a material allowance without checking project-specific guidance.
- Reporting excessive decimal places that the measurements do not justify.
Related Volume and Conversion Calculators
Frequently Asked Questions
What is the formula for calculating cubic feet?
For a rectangular object, multiply length × width × height after expressing all three dimensions in feet.
How do I calculate cubic feet from inches?
Multiply length, width and height in inches, then divide the cubic-inch total by 1,728.
How many cubic inches are in one cubic foot?
One cubic foot contains 1,728 cubic inches because 12 × 12 × 12 = 1,728.
How do I convert square feet to cubic feet?
Multiply the square-foot area by the depth or height in feet. A 100 ft² area that is 0.5 ft deep has a volume of 50 ft³.
How many cubic feet are in a cubic yard?
One cubic yard equals 27 cubic feet. Divide cubic feet by 27 to convert to cubic yards.
How do I calculate room volume in cubic feet?
Multiply the room's length, width and ceiling height in feet. A 12 ft × 10 ft × 8 ft room contains 960 ft³.
How do I calculate cubic feet for a cylinder?
Use π × radius² × height, with radius and height measured in feet. If you know the diameter, divide it by two first.
Is cubic footage the same as cubic feet?
Yes. Cubic footage is an informal phrase for a volume expressed in cubic feet.
Do I use inside or outside dimensions?
Use inside dimensions for usable capacity and outside dimensions for the total space an object occupies. State which measurement basis you used.
Should I round cubic feet up or down?
For a mathematical result, round according to the measurement precision. For purchasing materials, follow the supplier's package sizes and project-specific waste guidance.
Volume terminology and metric relationships were reviewed against the NIST SI Units–Volume guide. U.S. customary and metric conversion factors were checked against the 2026 NIST Handbook 44 conversion tables and the NIST Guide to the SI conversion factors. This article explains geometric volume; real usable capacity can differ because of wall thickness, internal components, irregular surfaces and measurement uncertainty.
