4 Cubic Feet to Gallons

Four cubic feet is 29.9221 US gallons

6,912 cubic inches, 231 per gallon

Four cubic feet is 29.9221 US gallons. The chain is short. A cubic foot is 1,728 cubic inches, a US gallon is 231 cubic inches, and 6,912 / 231 = 29.9221.

Multiply the other way and the same number appears: 4 x 7.4805 = 29.9221. Both routes use the same fact, that a cubic foot holds 7.4805 gallons.

The liquid side is fixed by definition. NIST Handbook 44, 2026 edition, Appendix C gives the general table of units that puts the US gallon at 231 cubic inches, and the NIST Guide to the SI, Appendix B.8 lists the same value in bold type, which marks an exact factor. A cubic foot is 28.316846592 liters, so 4 cubic feet is 113.2674 liters.

Read the gallon row first. Everything else on the page is built from that one decimal, which is why the same figure shows up on jug labels, drum charts and pump tickets.

Three gallons share the name and not the size

US liquid, US dry and imperial

Three different containers are all called a gallon, and they hold different amounts. Only one of them is the gallon you buy at a gas pump or pour from a milk jug.

The US liquid gallon is 231 cubic inches, or 3.785411784 liters. The US dry gallon is 268.8025 cubic inches, used for grain and produce. The imperial gallon is 277.4194 cubic inches, or 4.54609 liters, still used in the United Kingdom for fuel. The imperial gallon is about 20 percent larger than the US liquid gallon, which is why a UK mile per gallon figure does not compare to a US one. The liter both figures rest on is defined as one cubic decimeter in the BIPM SI Brochure, 9th edition, 2019.

Example with the dry gallon. Four cubic feet is 6,912 cubic inches. Divide by 268.8025 and the answer is 25.7140 dry gallons, which is what a bag of potting mix is measured in. Divide the same 6,912 by 277.4194 and the answer is 24.9153 imperial gallons.

So the sentence "4 cubic feet is 29.9221 gallons" is only true for the US liquid gallon. Add the word liquid when the number is going into a contract, a tank label or a recipe.

A box 24 by 24 by 12 inches is 4 cubic feet

Measure the inside faces

Most volume jobs start with a tape measure. A box 24 inches long, 24 inches wide and 12 inches deep holds 24 x 24 x 12 = 6,912 cubic inches, and 6,912 / 1,728 = 4 cubic feet, which is 29.9221 gallons.

That is the shape of a cooler, a storage tote, a planter, a sump chamber or a crate. Measure the inside faces, because the outside includes the wall. A box built from three quarter inch plywood loses 1.5 inches on each dimension, and 22.5 x 22.5 x 10.5 = 5,315.6 cubic inches, which is 3.08 cubic feet, a loss of about 23 percent.

Example, an odd shape. A planter 18 inches by 18 inches by 14 inches is 18 x 18 x 14 = 4,536 cubic inches, or 2.625 cubic feet, which is 19.64 gallons. Two of them hold 5.25 cubic feet, a little more than the 4 cubic feet on this page.

Keep all three measurements in the same unit before dividing. Inches and 1,728 go together, feet and 1 go together, and mixing the two is the error that turns a 4 cubic foot box into a 48 cubic foot box.

Buckets, drums and totes in cubic feet

What a 5 gallon pail holds

Buckets and drums are sold by the gallon, so the conversion runs the other way in most of these jobs. A standard 5 gallon pail holds 5 / 7.4805 = 0.6684 cubic feet. Four cubic feet fills that pail about 5.98 times.

A 55 gallon drum holds 55 / 7.4805 = 7.3524 cubic feet, so 4 cubic feet fills 54.4 percent of it. A 27 gallon storage tote holds 3.6094 cubic feet, which makes it a close match for a 4 cubic foot load.

A few more sizes turn up on job sites. A 40 gallon fresh water tank in a camper holds 5.3472 cubic feet, a 50 gallon rain barrel holds 6.6840 cubic feet, and a half barrel keg at 15.5 gallons holds 2.0721 cubic feet. A 275 gallon heating oil tank in a basement holds 36.762 cubic feet, so 4 cubic feet would fill about a ninth of it.

Container labels round down for safety, and a pail rated at 5 gallons usually holds a little more than that to the rim. Fill to the marked line, not to the top, when the liquid is being measured rather than carried.

What 4 cubic feet of water weighs

62.4 pounds per cubic foot

Water weighs 62.4 pounds per cubic foot at room temperature, so 4 cubic feet weighs 249.6 pounds. That is more than most people expect from a volume that fits in a small cooler, and it matters when the container sits on a floor, a shelf or a truck bed.

The gallon route gives a close check. Water is about 8.34 pounds per gallon, and 29.9221 x 8.34 = 249.6 pounds, the same figure to the tenth of a pound. The two constants are the same measurement written two ways.

Other liquids sit above or below that mark. Gasoline is about 6.3 pounds per gallon, so 4 cubic feet of it weighs roughly 188 pounds. Motor oil is about 7.5 pounds per gallon, which puts 4 cubic feet near 224 pounds. Antifreeze runs about 9.4 pounds per gallon, or 281 pounds for the same space.

Example, a shelf. A 4 cubic foot aquarium holds 29.92 gallons of water, and the water alone weighs 249.6 pounds. Add the glass, the gravel and the stand and the load passes 300 pounds, which is why the manual asks for a level floor rather than a shelf.

Soil, mulch and concrete at 4 cubic feet

Coverage depends on depth

Soil, mulch and concrete are sold by volume, and 4 cubic feet is a common bag size at a garden center. Spread it and the coverage depends on depth: cubic feet times 12, divided by depth in inches, gives square feet.

Example, mulch. Four cubic feet at 2 inches deep covers 4 x 12 / 2 = 24 square feet. At 1 inch it covers 48 square feet, and at 4 inches it covers 12. The same bag goes a lot further when it is spread thin.

Example, concrete. Four cubic feet is 0.1481 cubic yards, and an 80 pound bag yields about 0.6 cubic feet, so 4 / 0.6 = 6.67 bags, which means buying seven. A slab 4 feet by 4 feet at 3 inches needs 4 cubic feet exactly, since 16 x 3 / 12 = 4.

Bagged soil settles after watering, so buy about ten percent more than the math says. Concrete does not settle, and a short pour is a permanent problem, so round that one up to the next whole bag.

Price per gallon against price per cubic foot

Two quotes, one total

A price can be quoted per gallon or per cubic foot, and the two numbers are far apart even when the total is identical. Take $0.80 a gallon. Four cubic feet is 29.9221 gallons, so 29.9221 x 0.80 = $23.94 for the whole volume.

Per cubic foot the same liquid is 0.80 x 7.4805 = $5.98. A supplier who quotes $5.98 a cubic foot and a supplier who quotes $0.80 a gallon are asking the same money.

Example, a bigger order. Twenty cubic feet at $0.80 a gallon is 149.61 gallons and $119.69, which is 5 x $23.94 to the cent once the rounding is carried through. Buying 20 cubic feet at once usually comes with a lower unit price, but check which unit the discount is written against.

Fuel and propane are the exceptions that trip people up. Both are sold by the gallon in the United States, and both change volume with temperature, so a truckload measured on a cold morning holds slightly more mass than the same gallons on a hot afternoon. A delivery ticket that lists gallons and a tank chart that lists cubic feet describe the same liquid, and the conversion above is the bridge between them.

Liters, quarts and fluid ounces for the same space

Six numbers to keep

Six numbers cover almost every use of this page. One cubic foot is 1,728 cubic inches. One cubic foot is 7.4805 US gallons. One US gallon is 231 cubic inches. One cubic foot is 28.316846592 liters. One imperial gallon is 4.54609 liters. One cubic yard is 27 cubic feet.

The quarts row is worth a note because recipes use it. Four cubic feet is 119.6883 quarts and 3,830 fluid ounces. A dry quart is 67.2006 cubic inches, so the same space is 102.86 dry quarts, which is the number printed on a bag of potting mix.

Rounding matters at this size. The exact gallon figure repeats as 29.922077 and so on, so a label that says 29.9 gallons understates the volume by about 0.07 percent. Round up when the number is going into a tank, and round to taste when it is going into a paragraph.