1 gallons to cubic feet

One US gallon is 0.1336805556 cubic feet

A US gallon is exactly 231 cubic inches, and a cubic foot is 12 x 12 x 12 = 1,728 cubic inches. Divide the second by the first and one gallon occupies 0.1336805556 cubic feet. Turn the fraction over and a cubic foot holds 7.48051948051948 gallons. NIST Handbook 44, Appendix C, 2026 edition, prints the gallon as 231 cubic inches (exactly) and the cubic foot as 7.481 gallons.

The long decimal is not rounding noise. 231 / 1,728 reduces to 77 / 576, and 576 carries a factor of 3 that never divides out of ten, so the quotient repeats and stops nowhere. The metric route lands on the same place: one gallon is 3.785411784 liters, one cubic foot is 28.316846592 liters, and 3.785411784 / 28.316846592 = 0.1336805556.

Every row is the same multiplication: 55 x 0.1336805556 = 7.3524, and 1,000 x 0.1336805556 = 133.6806 cubic feet. The direction that earns its keep in practice is the reverse one, because a tank, a drum or a tote is labeled in gallons while the space it needs on a pallet, in a truck or on a shelf is measured in cubic feet.

Why the factor repeats instead of ending

The 231 is older than the cubic foot as a legal unit. The wine gallon of 1707 was defined as a cylinder 7 inches across and 6 inches deep, which comes to about 230.9 cubic inches and was rounded to 231. The foot joined the metric world much later: the international yard and pound agreement of 1959 fixed one inch at exactly 25.4 millimeters, and only then did the cubic foot become an exact metric quantity, 0.028316846592 cubic meters. Two units settled 250 years apart cannot produce a round ratio.

Rounding is where the money leaks. Four decimals, 0.1337, sit 0.0145 percent above the exact value, which is 0.15 gallons on a 1,000 gallon order and no reason to worry. Two decimals are a different story. Using 0.13 on 1,000 gallons returns 130 cubic feet instead of 133.68, short by 3.68 cubic feet, or 27.5 gallons of space. On a 275 gallon tote the shortcut gives 35.75 instead of 36.76 cubic feet, which is 7.6 gallons of capacity you did not order.

The working rule is simple in practice: carry the full 0.1336805556 while multiplying gallons, then round the answer to two or three decimals. Rounding the factor first and the answer second stacks two errors on top of each other, and on a shipping pallet that is the difference between a load that fits under a height limit and one that does not.

Container sizes in gallons, space in cubic feet

Most of the numbers people look up come from a container that is sold in gallons and stored in a space measured in feet. The table uses nominal capacity, so treat the figures as the space the contents need before walls, ribs, cages or a fill line take their share.

The drum is the row to memorize: 55 gallons is 7.35 cubic feet, roughly one third of a cubic yard, which is why three drums are a little short of a yard of space and four drums overshoot it. A 275 gallon tote is 36.76 cubic feet inside, yet its steel cage measures 48 by 40 by 46 inches, or 88,320 cubic inches and 51.11 cubic feet outside, so the cage alone eats 14 cubic feet of a truck bed that the liquid never fills.

Propane is the case where the label and the contents part company. A tank sold as 500 gallons is filled to about 80 percent, which is 400 gallons, or 53.47 cubic feet of liquid, and the remainder is vapor space that the tank needs for expansion on a warm day. Size the pad for the tank, not for the fill.

Sizing a tank from the gallons it must hold

Working backwards is a cube root for a cube and a division for everything else. A tank that must hold 100 gallons needs 100 x 0.1336805556 = 13.3681 cubic feet. The cube root of 13.3681 is 2.3731 feet, so a cube tank would be 28.48 inches on each inside face. For 55 gallons the same steps give 7.3524 cubic feet and a cube 1.9446 feet on a side, or 23.33 inches, which is close to the 23 inch inside height of a standard drum.

A round tank needs the height before the diameter. A 55 gallon drum is 7.3524 cubic feet, and a real drum stands about 33.5 inches tall, which is 2.7917 feet. Divide the volume by the height and the footprint is 2.6336 square feet. Divide by pi and take the square root: the radius is 0.9154 feet, or 10.98 inches, and the diameter is 21.97 inches. The drum you can buy is 22.5 inches across, so the arithmetic and the steel agree to within half an inch.

A rectangular tank is the easiest of the three. Take 100 gallons again, 13.3681 cubic feet, and a footprint 48 inches by 24 inches, which is 4 feet by 2 feet and 8 square feet. The liquid stands 13.3681 / 8 = 1.671 feet deep, or 20.05 inches. Add freeboard of 2 to 3 inches for a fill line and the tank should be about 23 inches tall.

Cubic yards, CCF and cubic meters on a utility bill

Water and sewer bills in the United States are usually read in CCF, which is one hundred cubic feet. One CCF is 748.05 gallons, so a household that uses 5 CCF in a month has used 3,740 gallons, or 500 cubic feet. The same bill in metric countries arrives in cubic meters, and one cubic meter is 264.172 gallons, or 35.3147 cubic feet.

Cubic yards matter for anything sold in bulk. One cubic yard is 27 cubic feet and 201.974 gallons, so 1,000 gallons of water is 133.6806 cubic feet and 4.9511 cubic yards, a little under five yards. A cubic yard of gravel at 1.4 tons displaces 202 gallons of water if it were a tank, which is the mental model for why a yard of stone fills a pickup bed but not a rain barrel.

An acre-foot is the unit that shows up in reservoir and irrigation talk, and the number is worth knowing: 43,560 square feet covered one foot deep is 325,851 gallons, which is 1,233,482 liters. A suburban lawn watered with one acre-foot a year would be using 893 gallons a day, which is why the unit appears in drought rules rather than on a garden hose.

Imperial and dry gallons in the same cubic foot

Not every gallon is the 231 cubic inch gallon. The US dry gallon is 268.8025 cubic inches, so it is 0.1555570 cubic feet and a cubic foot holds 6.4285 of them. The imperial gallon is 277.4194 cubic inches, or 4.54609 liters, so it is 0.1605436 cubic feet and a cubic foot holds 6.2288 of them. Both are larger than the liquid US gallon, by 16.4 percent and 20.1 percent respectively.

Ten imperial gallons is therefore 1.6054 cubic feet, not the 1.3368 that ten US gallons occupy, and a UK can that says 10 gallons is 12.01 US gallons. The dry gallon is the one that survives on potting soil, grain and produce: a 1 cubic foot bag of soil is labeled 6.43 dry gallons, and a 7.5 gallon nursery pot is 1.0026 cubic feet by the liquid gallon and 1.1667 by the dry one. Buy soil by the cubic foot and the ambiguity disappears.

One practical consequence: a marine or RV tank rated in imperial gallons holds 20 percent more than the same number of US gallons suggests, and a fuel dock in the Bahamas or the UK that quotes imperial gallons is selling 4.546 liters at a time. Convert to liters first when a document crosses a border, because liters are the same everywhere and gallons are not.

Weight, floor load and pressure at the bottom

A gallon of water weighs about 8.33 pounds, a figure the USGS Water Science School also uses, so a cubic foot weighs 62.4 pounds and 1,000 gallons weigh 8,330 pounds before the tank. That mass is the reason a 275 gallon tote on a pallet is a forklift job and a 55 gallon drum is 458 pounds of water plus 20 pounds of steel, which is a hand truck job with two people.

Footprint decides whether a floor complains. A 1,000 gallon tank holds 133.68 cubic feet; spread that over a 20 square foot base and the water stands 6.68 feet deep, which is a tall tank, and the pressure at the bottom is 2.89 psi, because fresh water gains 0.433 psi for every foot of depth. Spread the same 8,330 pounds over 20 square feet and the floor sees 417 pounds per square foot, well past the 40 to 50 pounds per square foot a wood deck is built for, so the tank belongs on a slab or a steel frame.

Depth rather than area drives pressure, which is why a tall narrow tank needs thicker walls than a shallow wide one of the same volume. A 55 gallon drum stands 33.5 inches tall and sees 1.21 psi at the bottom, while a 6 foot deep rainwater tank sees 2.6 psi, so the drum can be thin steel and the tall tank cannot.

Checks before you order, fill or ship

Four checks catch nearly every expensive mistake. First, measure inside faces, because a quarter inch of wall on each side of a 12 inch cube removes 12 percent of the volume, and on a 1,000 gallon tank the same wall thickness can cost more than 20 gallons of capacity. Second, convert to cubic feet before comparing prices, since a tote quoted at 275 gallons and a tank quoted at 40 cubic feet are 36.76 and 40 cubic feet, a 9 percent difference that the gallon number hides.

Third, allow for what goes in besides liquid: gravel at 15 pounds per gallon of volume, a pump, a heater or a foam liner all displace water, and a tank filled to the rim with cold water will overflow when it warms up if there is no expansion space. Fourth, write the unit on the order. Gallons, imperial gallons and cubic feet all appear on the same purchase order in the marine and brewing trades, and the gap between the first two is 20 percent.

The converter on this page handles the arithmetic in both directions. Pick the gallon you are holding, US liquid, US dry or imperial, type gallons or cubic feet, and the other units follow, along with liters, cubic yards and the weight of the contents as water. Below that, the same gallons turn into a square footprint or a round diameter at whatever height you plan to fill to, which is the number a tank stand or a shelf needs.