The unit
What is a cubic foot?
A cubic foot is the amount of space taken up by a cube measuring one foot along every edge. It is a unit of volume, which means it describes three dimensions at once rather than a flat surface. You will see it written as ft³, cu ft, CF or CFT, and all four mean exactly the same thing.
The unit is standard in the United States and still widely used across the United Kingdom and Canada for appliances, storage and freight. Most other countries measure volume in cubic metres, which is why this calculator gives you both figures side by side.
Is one cubic foot really 12 × 12 × 12? Yes, when you are working in inches. A foot contains twelve inches, so a one-foot cube measures twelve inches on each side: 12 × 12 × 12 = 1,728 cubic inches. That number, 1,728, is the single most useful figure on this page, because it is how you turn any measurement in inches into cubic feet.
Cubic feet compared with square feet
Square feet and cubic feet are easy to confuse because they share a name, but they answer different questions. Square footage tells you how much floor, wall or ground a thing covers. Cubic footage tells you how much space it fills. A rug is measured in square feet. A refrigerator is measured in cubic feet.
The relationship between them is simply height. Multiply an area in square feet by a height in feet and you have cubic feet. Divide a volume in cubic feet by a height in feet and you get back to square feet. There is no fixed conversion between the two, because one of them is missing a dimension.
How big is a cubic foot in practice?
It helps to have a physical reference. One cubic foot is roughly the size of a milk crate, a small microwave cavity, or a shoebox that has been made a little deeper on every side. A standard bathtub holds somewhere near 42 cubic feet. A typical American refrigerator sits between 18 and 26 cubic feet. A 20-foot shipping container holds about 1,170.
The reason
Why measuring cubic feet matters
Anything you buy by the truckload, the bag or the container is really being sold by volume, even when the label says otherwise. Getting the cubic footage right is the difference between one delivery and two, or between the moving truck you booked and the one you actually needed.
The most common reasons people work in cubic feet:
- Moving and storage. Truck sizes and storage units are rated in cubic feet, and removal firms often quote by volume rather than weight.
- Landscaping. Mulch, topsoil, compost and gravel are sold by the bag or the cubic yard, both of which start life as a cubic foot figure.
- Construction. Concrete, fill and insulation are all ordered by volume, and over-ordering concrete is expensive while under-ordering ruins a pour.
- Freight. Carriers charge on whichever is larger, actual weight or volumetric weight, so knowing your cubic footage tells you which one you are about to pay for.
- Heating and cooling. Sizing an air conditioner, extractor fan or air purifier depends on the air volume of the room, not its floor area.
- Appliances and aquariums. Capacity is quoted in cubic feet or gallons, and both come from the same measurement.
The tool
How to use this Online cubic feet calculator
- Pick the shape that matches what you are measuring. Most things are boxes, but stockpiles are cones, tanks are cylinders, and a loft space is often a triangular prism.
- Type in your measurements. Each field has its own unit, so you can enter a length in feet and a depth in inches without converting anything first.
- Use whatever notation you have. The fields accept plain decimals, fractions such as
6 1/2, and mixed measurements written the way a tape measure reads them, such as5' 6"or5 ft 6 in. - Set a quantity if you have several identical items, and the total updates automatically.
- Add items to your list when you are totalling a whole move or a mixed order. Each entry keeps its own dimensions and the running total sits at the bottom.
- Open the panels for weight, bag counts, freight figures or the full worked calculation.
Copy link saves your numbers into the web address. Send that link to a colleague or paste it into a quote, and the calculator reopens with exactly the same measurements filled in.
The method
How to calculate cubic feet by hand
For any box-shaped space the calculation is a single line. Measure the length, the width and the height in feet, then multiply all three together.
The order does not matter. What does matter is that every measurement is in the same unit before you multiply, which is the step most people skip.
Worked example — a walk-in closet
- Length: 7 ft
- Width: 4.5 ft
- Height: 9 ft
- 7 × 4.5 × 9 = 283.5
The closet holds 283.5 cubic feet of space.
Volume formulas for every shape
Not everything is a box. These are the formulas the calculator uses, with all measurements taken in feet so the answer lands in cubic feet directly.
| Shape | Formula | What it suits |
|---|---|---|
| Box or rectangular prism | l × w × h | Rooms, cartons, truck beds, raised beds |
| Cube | a³ | Anything with three equal sides |
| Cylinder | π × r² × h | Tanks, sonotubes, round planters, silos |
| Capsule | π × r² × ((4/3)r + h) | Propane tanks, rounded-end vessels |
| Cone | (1/3) × π × r² × h | Stockpiles of gravel, sand or bark |
| Tapered cylinder | (1/3) × π × h × (r² + R² + rR) | Buckets, plant pots, hoppers |
| Sphere | (4/3) × π × r³ | Spherical tanks, balls, domes |
| Hemisphere | (2/3) × π × r³ | Domed roofs, half-round basins |
| Triangular prism | ½ × b × t × l | Loft and gable spaces, wedge voids |
| Pyramid | (1/3) × l × w × h | Four-sided tapers |
| Area × depth | area (sq ft) × depth (ft) | When the square footage is already known |
Measuring an irregular shape
Awkward rooms and oddly shaped beds do not need a special formula. Break the space into rectangles, cylinders and triangles that you can measure, calculate each piece separately, and add the results together. An L-shaped room is two rectangles. A garden bed that curves at one end is a rectangle plus a half-circle.
The list feature above is built for exactly this. Measure each section, add it to the list, and read the combined total at the bottom rather than keeping figures on paper.
Inches
How to calculate cubic feet from inches
Most household items are measured in inches, so this is the conversion people need most often. There are two routes to the same answer, and both are correct.
Method one: convert the measurements first
Divide each measurement by 12 to turn inches into feet, then multiply the three results together.
Method two: convert the answer
Multiply the three inch measurements together to get cubic inches, then divide by 1,728.
The figure 1,728 is simply 12 × 12 × 12. You are dividing by twelve once for each dimension, and doing it in a single step is faster and less prone to rounding drift.
Worked example — a microwave cavity
- Interior width: 20 in
- Interior depth: 16 in
- Interior height: 11 in
- 20 × 16 × 11 = 3,520 cubic inches
- 3,520 ÷ 1,728 = 2.04
The cavity is 2.04 cubic feet, which is how it would be advertised.
Appliance capacities use interior measurements. A refrigerator advertised at 22 cubic feet refers to usable internal space, not the size of the cabinet you need to fit into your kitchen. Measure inside the door seals, not the outside of the case.
Converting cubic inches to cubic feet
If you already have a volume in cubic inches, divide by 1,728. To go the other way, multiply cubic feet by 1,728. So 5,000 cubic inches is 2.89 cubic feet, and 3 cubic feet is 5,184 cubic inches.
Other units
Working from metres, yards and centimetres
The principle never changes: get every measurement into feet, then multiply. Only the conversion factor differs.
| You measured in | To get feet | To go straight to cubic feet |
|---|---|---|
| Inches | ÷ 12 | cubic inches ÷ 1,728 |
| Yards | × 3 | cubic yards × 27 |
| Centimetres | ÷ 30.48 | cubic centimetres ÷ 28,316.85 |
| Metres | × 3.28084 | cubic metres × 35.3147 |
| Millimetres | ÷ 304.8 | cubic millimetres ÷ 28,316,847 |
From yards
A yard is three feet, so a cubic yard is 3 × 3 × 3 = 27 cubic feet. This is the number to remember when ordering landscaping or concrete, because suppliers quote in cubic yards while you almost certainly measured in feet. Divide your cubic feet by 27 to place the order.
From metres
One cubic metre equals 35.3147 cubic feet. Freight paperwork calls this figure CBM, and it is the standard unit for sea and air cargo everywhere outside the United States. To go the other way, multiply cubic feet by 0.0283168.
From centimetres
Divide each centimetre measurement by 30.48 to get feet, or multiply the three measurements together and divide the result by 28,316.85. This is the usual route when you are working from a product specification sheet written for a metric market.
Mixed feet and inches
Tape measures do not read in decimals. A ceiling is 8 ft 4 in, not 8.33 ft. To convert by hand, divide the inches by twelve and add the result to the feet, so 8 ft 4 in becomes 8 + (4 ÷ 12) = 8.33 ft. The calculator above accepts 8' 4" directly, which removes the step entirely.
Conversions
Converting cubic feet into other units
Cubic feet to cubic yards
Divide by 27. Bulk materials are almost always delivered by the cubic yard, and most suppliers set a minimum order of one yard, so it is worth knowing whether your project is a bag job or a delivery job before you call.
Cubic feet to square feet
These measure different things, so there is no direct conversion. What you can do is divide the volume by the height. A room of 1,200 cubic feet with a ten-foot ceiling has 120 square feet of floor. In landscaping the same maths tells you coverage: 40 cubic feet of mulch spread three inches deep covers 160 square feet, because three inches is a quarter of a foot and 40 ÷ 0.25 = 160.
Cubic feet to gallons and litres
One cubic foot holds 7.48 US gallons, 6.23 imperial gallons, or 28.32 litres. This is the conversion for tanks, ponds and aquariums. A tank measuring 4 ft by 2 ft by 2 ft holds 16 cubic feet, which is roughly 120 US gallons.
Cubic feet to weight
Volume alone cannot give you weight; you also need the density of the material. Multiply the cubic feet by the density in pounds per cubic foot, then divide by 2,000 for US tons. The weight panel in the calculator does this for the materials people order most.
| Material | Pounds per cubic foot | One cubic yard weighs about |
|---|---|---|
| Water | 62.4 | 1,685 lb |
| Concrete, wet mix | 150 | 4,050 lb |
| Gravel | 105 | 2,835 lb |
| Sand, dry | 100 | 2,700 lb |
| Topsoil | 76 | 2,050 lb |
| Compost | 30 | 810 lb |
| Bark mulch | 20 | 540 lb |
| Household goods | 7 | 190 lb |
Moving and freight
Working out cubic feet for a move or a shipment
Removal companies size trucks by volume, and the estimate they give you over the phone is only as good as the inventory it came from. Measuring every item is unnecessary; measuring your boxes and your six largest pieces of furniture gets you within a sensible margin.
Standard moving box sizes
| Box | Typical dimensions | Volume |
|---|---|---|
| Book or small | 16 × 12 × 12 in | 1.33 ft³ |
| Medium | 18 × 18 × 16 in | 3.00 ft³ |
| Large | 24 × 18 × 18 in | 4.50 ft³ |
| Extra large | 24 × 20 × 22 in | 6.11 ft³ |
| Wardrobe | 24 × 21 × 46 in | 13.42 ft³ |
Add each box type to the list above with its quantity and the total builds itself. A useful rule of thumb: a one-bedroom flat comes to roughly 300 to 450 cubic feet, a two-bedroom home to 600 to 900, and a four-bedroom house to 1,800 or more. Always book slightly larger than your number, because nothing packs perfectly.
Volumetric weight for couriers
Air freight and parcel carriers charge on dimensional weight when a package is bulky but light. The common formulas are cubic inches divided by 166 for pounds, or cubic centimetres divided by 5,000 for kilograms. Compare that figure against the actual weight; you will be billed for whichever is higher. Divisors vary between carriers, so check the rate card for anything expensive.
Container capacity
A 20-foot container holds roughly 1,170 cubic feet, a 40-foot standard around 2,390, and a 40-foot high cube about 2,690. Real-world loading rarely exceeds 80 per cent of these figures once pallets, dunnage and irregular cartons are accounted for.
Garden and site
Soil, mulch, gravel and concrete
Landscaping volumes follow one pattern: work out the area you are covering, decide how deep the layer needs to be, convert that depth to feet, and multiply. The depth is where most errors creep in, because it is quoted in inches while everything else is in feet.
Mulch
Bark mulch is normally laid two to three inches deep, or four inches where you are suppressing established weeds. Bagged mulch usually comes in two cubic foot bags, so divide your total by two to get the bag count. Bulk mulch is sold by the cubic yard, which is 27 cubic feet, or about thirteen and a half bags.
Worked example — a border bed
- Bed: 24 ft long, 5 ft wide
- Depth wanted: 3 in, which is 0.25 ft
- 24 × 5 × 0.25 = 30 cubic feet
- 30 ÷ 2 = 15 bags, or 30 ÷ 27 = 1.11 cubic yards
Order 15 bags, or round up to a yard and a half if buying bulk.
Topsoil and compost
Raised beds need filling to their internal dimensions, not their outer frame. A bed measuring 8 ft by 4 ft with 12 inches of usable depth takes 32 cubic feet. Bagged soil is commonly sold in 1.5 cubic foot bags, so that is 22 bags, at which point a bulk delivery is usually cheaper. Soil settles noticeably in the first season, so add ten per cent.
Gravel and crushed stone
Decorative gravel is laid two inches deep, while a driveway base wants four to six inches over a compacted sub-base. Gravel is heavy at roughly 105 pounds per cubic foot, so check the load rating before ordering a full yard; one cubic yard is close to 2,835 pounds.
Concrete
Slabs are calculated as length × width × thickness, with thickness converted from inches to feet. A pad measuring 12 ft by 10 ft at 4 inches thick works out at 12 × 10 × 0.333 = 40 cubic feet, which is 1.48 cubic yards.
Bagged concrete yields far less than people expect. An 80 lb bag makes about 0.60 cubic feet, a 60 lb bag about 0.45, and a 40 lb bag about 0.30. That 40 cubic foot pad would need 67 bags of the 80 lb mix, which is the point where ready-mix delivery becomes the sensible option. Order five to ten per cent extra for spillage and uneven sub-grade, and remember that ready-mix suppliers usually have a minimum order of one cubic yard.
Questions
Common questions about cubic feet
How do you calculate cubic feet?
Measure length, width and height in feet and multiply all three together. If your measurements are in inches, either divide each one by twelve first, or multiply them together and divide the result by 1,728.
Is one cubic foot the same as 12 × 12 × 12?
Yes, in inches. A cube with twelve-inch sides contains 1,728 cubic inches, and that volume is one cubic foot. Written in feet, the same cube is 1 × 1 × 1.
How many square feet does one cubic foot cover?
It depends entirely on the depth of the layer. Spread one inch deep, a cubic foot covers 12 square feet. At two inches it covers 6, at three inches 4, and at six inches just 2. Divide the volume by the depth in feet to find the coverage.
How many cubic feet are in a 10 × 10 room?
A 10 by 10 foot room with a standard 8-foot ceiling holds 800 cubic feet. With a 9-foot ceiling it is 900, and with a 10-foot ceiling it is 1,000. Floor area alone is not enough; you always need the height.
What is the volume of a 5 ft × 5 ft × 5 ft cube?
125 cubic feet, because 5 × 5 × 5 = 125. That is also 4.63 cubic yards or 3.54 cubic metres.
What is the volume of a 1 ft × 1 ft × 1 ft cube?
Exactly one cubic foot. It is the definition of the unit, and it equals 1,728 cubic inches or 28.32 litres.
How do I calculate cubic metres from centimetres?
Multiply the three centimetre measurements together to get cubic centimetres, then divide by 1,000,000. A carton of 60 × 40 × 30 cm is 72,000 cubic centimetres, which is 0.072 cubic metres, or 2.54 cubic feet.
What is CFT, and is it different from cubic feet?
CFT is shorthand for cubic feet, used most often in freight and construction in South Asia and the Middle East. It refers to the same unit; there is no difference in the calculation.
How do I find the cubic footage of a room for air conditioning?
Multiply the floor length, floor width and ceiling height in feet. That air volume is what an HVAC engineer sizes equipment against, along with insulation quality, window area and climate. Volume alone gives you a starting figure, not a specification.
Can I mix feet and inches in one measurement?
Yes. Type it the way your tape measure reads, such as 7' 3", and the calculator converts it. Working by hand, divide the inches by twelve and add the result to the feet.