Convert ft³ to in³ cubic feet ↔ cubic inches Free Online Secure
Type a value in cubic feet and read it in cubic inches at once. The factor is exact by definition, the arithmetic happens in your browser, and nothing is sent anywhere.
Nothing uploaded
Common values — Convert ft³ to in³ (cubic feet ↔ cubic inches)
| ft³ | in³ |
|---|---|
| 1 | 1728 |
| 2 | 3456 |
| 3 | 5184 |
| 5 | 8640 |
| 10 | 17280 |
| 20 | 34560 |
| 50 | 86400 |
| 100 | 172800 |
Where these units come from
The litre has an awkward history. From 1901 it was defined as the volume of one kilogram of pure water at its densest, which sounds elegant but came out at 1.000028 cubic decimetres — close enough to be confusing and far enough to spoil careful work. In 1964 the definition was abandoned and the litre became exactly one cubic decimetre, which it has been ever since. The gallon has a messier story still: the US gallon descends from the English wine gallon of 231 cubic inches, while Britain redefined its own in 1824 as the volume of ten pounds of water. Nobody reconciled the two, so a US gallon is 3.785411784 litres and an imperial gallon 4.54609 — about a fifth larger. The gallon, pint, cup, fluid ounce and spoons on this page are the US ones.
Where you meet them
Millilitres and litres run through daily life almost invisibly: bottles, fuel, paint, dosage, the capacity of a kettle. Cubic metres belong to water bills, concrete, shipping and the air a ventilation system has to move. Cubic centimetres name engine displacement, cubic feet appear in freight and in appliance capacities, and cups and spoons live almost entirely in recipes — which is exactly where the difference between a US cup and a metric one quietly ruins a cake.
Questions people ask
Where are cubic feet used?
In the United States for natural gas billing, refrigerator and freezer capacity, and the interior volume of shipping containers, and worldwide for airflow, where fans are rated in cubic feet per minute. A cubic foot is exactly 28.316846592 litres, so a small fridge of 4 cubic feet holds about 113 litres.
How do cubic inches relate to engine size?
A cubic inch is exactly 16.387064 millilitres, so 61 cubic inches is almost exactly a litre. American engines were long described in cubic inches: a 350 is about 5.7 litres. The figure states displacement, the total volume swept by the pistons, and not the power of the engine.
Is the answer exact?
Where both units are defined in terms of one another by whole numbers, yes — the page says so above the figure, and the only rounding is in how many digits are shown. Where the ratio has no finite decimal, the page shows twelve significant digits and says the relation is approximate rather than pretending otherwise.
Does anything I type leave my device?
No. The arithmetic runs in your browser; nothing is uploaded and there is no server to upload it to. Load the page once and it keeps working with the network switched off.
Speaker boxes, fans and 1,728: when a cubic foot meets the inch
Audio designers talk about a speaker enclosure of 1.5 cubic feet, then draw it in inches for the saw. Fan makers rate airflow in cubic feet per minute, while the case they sit in is measured in cubic inches. The bridge is a whole number: a cubic foot is 12 inches by 12 by 12, which is 1,728 cubic inches. To convert ft³ to in³ you multiply by 1,728, so 1.5 ft³ is 2,592 in³. This page multiplies as you type, and the text below shows how the factor works in enclosures, airflow and a famous anecdote about the number 1,729.
The page covers the rule with examples, a short note on each unit, a comparison, a tour of enclosures and airflow, and the slips to avoid. All arithmetic happens in your browser; nothing you enter is sent anywhere.
How to convert ft³ to in³: multiply by 1,728
The rule
A foot is exactly 12 inches, so a cubic foot is 12 times 12 times 12, which is 1,728 cubic inches. To convert ft³ to in³, multiply the cubic feet by 1,728. So 0.5 ft³ is 864 in³, 2 ft³ is 3,456 in³ and 3.5 ft³ is 6,048 in³. To go the other way, divide cubic inches by 1,728.
Worked examples
A sealed subwoofer box of 1 ft³ has 1,728 in³ inside. A driver that displaces 0.05 ft³ takes up 86.4 in³. A computer case of 0.7 ft³ holds 1,210 in³. If you want a rough figure, multiply by 1,700 and add a little: 4 ft³ is about 6,800, plus 112, giving 6,912 exactly.
Why not 12
The number 12 converts lengths from feet to inches. A volume multiplies three lengths, so the factor is 12 cubed. Using 12 on a volume leaves the answer 144 times too small, and a box built to that figure would be far too small.
A quick sanity check
The cubic inch is the small unit, so the number grows by about seventeen hundred times. If your “convert ft³ to in³” calculation result grew by 12 or 144 times, you used the length or area factor.
The cubic foot
Twelve inches in each direction
The cubic foot is 28.317 litres. It is used for enclosures, airflow, refrigerators, soil and gas in the United States, and it is the unit in which loudspeaker designers state internal volume.
Where it appears
Audio enclosures, HVAC specifications, appliance capacities and shipping.
The cubic inch
One inch in each direction
The cubic inch is 16.387 cm³. Small components, ports, displacements and internal cavities are given in it. It is also the unit in which woodworkers calculate what comes out of a block.
Where it appears
Parts catalogues, driver specifications, engine sizes and cabinet plans.
Cubic foot and cubic inch compared
A cubic foot holds 1,728 cubic inches, so the figure in inches is much larger than the figure in feet: 3 ft³ is 5,184 in³. A designer who works out a port volume in cubic inches has to subtract it from an enclosure volume given in cubic feet, and the factor has to be right to avoid an error of several percent.
The factor is an integer, so no rounding is needed. The danger is only in the choice: 1,728, not 12.
Where the conversion appears
Speaker enclosures
A sealed enclosure with an internal volume of 1 ft³ is a cube of 12 inches inside. With 3/4 inch walls, the outside measures 13.5 inches on each side, which is 2,460 in³ or 1.42 ft³. A driver or port inside takes some of the volume, so a builder adds its displacement. Everything is worked in cubic inches for the saw, and in cubic feet for the specification.
Fans and airflow
A 120 mm PC fan moves about 60 cubic feet of air per minute, 103,680 in³. A case of 0.7 ft³ has its air replaced about every second at that rate, though real flow through a case is far lower. A kitchen hood of 300 CFM clears a kitchen of 1,440 ft³ every 4.8 minutes. When you convert ft³ to in³, you can compare the fan with the space it serves.
Racks and cabinets
A 42U server cabinet of 600 by 1,070 by 2,000 mm is roughly 1.28 m³, or 45 ft³, 78,000 in³. Facilities planners calculate cooling for the room in cubic feet per minute and for the equipment in inches, so conversions come up often.
The number 1,729
The mathematician G. H. Hardy told of visiting the Indian mathematician Srinivasa Ramanujan in hospital and remarking that his taxi number, 1,729, seemed dull. Ramanujan replied that it was the smallest number that is the sum of two cubes in two different ways: 1 cubed plus 12 cubed, and 9 cubed plus 10 cubed. The first of those, 12 cubed, is 1,728, the number of cubic inches in a cubic foot. It is a pleasant coincidence that the conversion factor sits right next to the famous number.
Fuel and storage tanks
A fuel tank of 2 ft³ holds 14.96 US gallons, since a cubic foot is 7.48 gallons. In inches that is 3,456 in³, and a gallon is 231 in³. Boat builders and aircraft designers move between the three units: a tank of 15 gallons, 3,465 in³, 2.0 ft³. The numbers differ by under half a percent, which is why rounding matters when tanks are certified.
Small loads and boxes
A box of 18 by 12 by 12 inches holds 2,592 in³, 1.5 ft³. A moving carton of 24 by 18 by 18 holds 7,776 in³, 4.5 ft³. Movers sell cartons by cubic feet, while the planning of how many fit in a van uses the van's volume in cubic feet. A converter lets you check the figures when you want to compare the volume of a single carton with a drawing in inches.
In a spreadsheet
Enter the cubic feet in column A and use =A2*1728 in column B. For the reverse, =B2/1728. Add a column to subtract the displacement of each driver or port in cubic inches. Format the result with one decimal for large volumes and none for small ones, and keep the original column so that you can retrace each step.
Rounding
The factor 1,728 is exact, so rounding is a choice. If the source gives 1.5 ft³, you have two significant figures, so 2,600 in³ is enough, though 2,592 is exact. Round at the end of the calculation, not at each step, to avoid compounding small errors, and state the rounding in the notes for the design.
Multiplying in your head
To multiply by 1,728, think of 1,700 plus 28. For 3 ft³, 5,100 plus 84 gives 5,184. For 5, 8,500 plus 140 gives 8,640. The method works for any number of cubic feet and gives the exact result. A second way is to multiply by 12 three times, which is slower but equally reliable for decimals.
Reference values
0.1 ft³ is 173 in³, 0.25 ft³ is 432 in³, 0.5 ft³ is 864 in³, 1 ft³ is 1,728 in³, 2 ft³ is 3,456 in³, 5 ft³ is 8,640 in³ and 10 ft³ is 17,280 in³. If you convert ft³ to in³ and land far from this ladder, repeat the multiplication.
Checking by reversing
To make sure your “convert ft³ to in³” calculation result is right, divide it by 1,728. If 1.5 ft³ gave 2,592 in³, then 2,592 divided by 1,728 returns 1.5. A second check is the size of the result: it should be about seventeen hundred times larger than the figure in cubic feet, not twelve or 144 times.
Air conditioning and airflow per ton
A common rule of thumb gives about 400 CFM of airflow for each ton of cooling. A 3 ton unit therefore moves 1,200 ft³ per minute, 2,073,600 in³. Installers measure duct sizes in inches and airflow in cubic feet per minute, so the two units appear together on every design sheet. When a duct run is described by its cross-section in square inches, a “convert ft³ to in³” calculation step helps to check the air speed.
Bathroom fans
A simple guide for a small bathroom is one cubic foot per minute for each square foot of floor, so a 50 ft² room needs a fan of 50 CFM. In cubic inches, that is 86,400 per minute. Fans are rated in CFM and sones, and the quiet ones cost more. If you convert ft³ to in³ for a duct fitting, you can see how many cubic inches of air must squeeze through each opening each second.
Cabinets and humidors
A cigar humidor of 1 ft³ holds 1,728 in³ and stores about 100 cigars. A wine fridge of 3.5 ft³ has 6,048 in³ and holds about 30 bottles. A safe of 2 ft³ has 3,456 in³. In every case the maker states the capacity in cubic feet, and the buyer wants to know whether a given object, measured in inches, will fit. Multiplying the three dimensions in inches and dividing by 1,728 gives the answer.
Sealed and ported enclosures
A sealed enclosure behaves like a spring: the smaller the volume, the stiffer the air. A bass driver that suits 1.5 ft³, 2,592 in³, might need 3 ft³, 5,184 in³, for a ported design with a lower cutoff. Designers use software that takes inches for dimensions and cubic feet for volume, so most programs have the factor 1,728 built in, and a manual check is a good habit.
Fireplaces and flues
A fireplace firebox of 30 by 24 by 18 inches holds 12,960 in³, which is 7.5 ft³. A chimney needs to move the combustion air, typically a few hundred cubic feet per minute at full burn. Masons and stove installers work in inches for the opening and in cubic feet for the room that the stove must heat, so the two scales meet whenever someone sizes an installation.
Ice chests and coolers
A cooler marked 48 quarts has an interior of about 1.6 ft³, 2,765 in³, which is roughly 45 litres. A 100 quart cooler holds 3.3 ft³, 5,760 in³. Quarts, cubic feet and cubic inches all appear in the product description, and a buyer who wants to know if a particular box of drinks will fit uses the inch dimensions and the “convert ft³ to in³” calculation step to check against the quoted capacity.
Wall thickness and net volume
An enclosure with outside dimensions of 15 by 12 by 10 inches has a gross volume of 1,800 in³, 1.04 ft³. With walls of 3/4 inch, the inside is 13.5 by 10.5 by 8.5, about 1,205 in³, 0.70 ft³. The gap of 33 percent shows why the walls count. A calculation of the internal volume is always the one that matters for sound.
Driver and port displacement
A 10 inch woofer displaces about 0.04 ft³, 69 in³, and a round port tube of 3 inches diameter and 8 inches long takes 56.5 in³, 0.033 ft³. Together they take 125 in³ from the enclosure, about 7 percent of 1,728. A design volume of 1 ft³ net therefore requires 1.07 ft³ gross. Builders add each displacement in cubic inches because the parts are measured with a ruler.
Air changes in a room
A room of 12 by 15 by 8 feet has 1,440 ft³, which is 2,488,320 in³. A fan of 144 CFM changes the air once every 10 minutes. Standards for kitchens and bathrooms specify air changes per hour, or a minimum CFM per square foot, and the volume of the room in cubic feet is the starting point. Cubic inches rarely appear, but the arithmetic gives you a sense of how big the numbers become.
Blower door tests
A house of 20,000 ft³ tested at 2,000 CFM at 50 pascals has 6 air changes per hour, since 2,000 times 60 divided by 20,000 is 6. In cubic inches the house holds 34,560,000 in³, a figure that nobody uses, though it illustrates the scale. Energy auditors calculate in cubic feet, and it is the home's volume that sets the benchmark for leakage.
Dust collection and workshops
A workshop dust collector of 600 CFM moves 1,036,800 in³ of air per minute. A small bandsaw may need only 350 CFM at its port. The collector must be sized for the machine with the highest demand, and the duct volume determines how fast air moves. Woodworkers describe their ducts in inches and the airflow in cubic feet, so the conversion appears often when planning.
Vacuum and compressor displacement
An air compressor with a pump displacement of 12 in³ per revolution turning at 1,000 rpm moves 12,000 in³ per minute, or 6.9 CFM. A vacuum pump of 2 CFM displaces 3,456 in³ per minute. Specifications in cubic feet per minute give the real delivered flow, while the pump data lists swept volume in cubic inches, so a “convert ft³ to in³” calculation step links them.
Gas in a cylinder
A tank rated at 80 cubic feet of gas does not hold that volume physically; it holds compressed gas that would fill 80 ft³ at atmospheric pressure. The tank's internal volume might be 0.4 ft³, 691 in³, and the pressure 200 times atmospheric. Divers and welders learn the difference between the nominal gas capacity and the internal volume early, and it is the conversion between cubic feet and cubic inches that appears in the first lesson.
More values for convert ft³ to in³
A longer list of conversions
If the value you need is not in the first list, these further conversions may be close enough to read off directly:
- 0.1 ft³ = 172.8 in³
- 0.5 ft³ = 864 in³
- 3 ft³ = 5,184 in³
- 4 ft³ = 6,912 in³
- 7 ft³ = 12,096 in³
- 15 ft³ = 25,920 in³
- 20 ft³ = 34,560 in³
- 75 ft³ = 129,600 in³
- 200 ft³ = 345,600 in³
- 500 ft³ = 864,000 in³
- 2,000 ft³ = 3,456,000 in³
- 10,000 ft³ = 17,280,000 in³
Mistakes when you convert ft³ to in³
Using 12
That is the linear factor. For volumes, multiply by 1,728.
Using inside and outside dimensions together
Volume specifications refer to the inside. Subtract wall thickness before multiplying.
Forgetting displacement
Drivers, ports and braces take up room. Net volume is lower than gross volume.
Quick answers
How many cubic inches are in a cubic foot?
1,728.
How do I convert ft³ to in³?
Multiply by 1,728.
How many cubic feet are in a cubic inch?
0.000579.
What is 2 ft³ in cubic inches?
3,456 in³.
Does the number I type leave my device?
No, it stays in your browser.
More pages and a closing note
For other volume conversions, see Convert ft³ to L, Convert ft³ to m³, Convert cm³ to in³, Convert in³ to cm³, Convert km to mi, Convert mi to km, Convert °C to °F, Convert °F to °C, Convert N·m to lb·ft. The opposite direction is Convert in³ to ft³.
In short, you convert ft³ to in³ by multiplying by 1,728, which is twelve cubed, and writing the unit beside the answer. Your figure is calculated on your own device, with no account and no upload.