Gallons to Cubic Feet Converter

Gallons and cubic feet describe the same thing, volume, but they come from different habits. Gallons are common on pumps, drums, aquariums, sprayers, water heaters, and chemical containers. Cubic feet appear when a space is measured by length, width, and depth: a sump pit, planter bed, cabinet cavity, room volume, excavation, or storage bin. This converter starts with US liquid gallons and returns cubic feet, plus cubic inches, liters, cubic meters, and the gallons-per-cubic-foot factor used by the form.

The page is gallons-first. If a tank label says 55 gal and a placement guide asks for cubic feet, enter the gallons here. If you measured a rectangular container in feet and need gallons instead, multiply cubic feet by 7.48051948051948 or use the related cubic feet to gallons calculator. For wider comparisons, the volume converter and gallon calculator link this conversion to liters, quarts, pints, cups, and other liquid units.

Why gallons connect to cubic feet

A cubic foot is the volume of a cube one foot on each side. Since a foot is 12 inches, one cubic foot contains 12 × 12 × 12 cubic inches, or 1,728 in³. A US liquid gallon is 231 cubic inches. Those definitions make the conversion a ratio between two volumes expressed in cubic inches:

$\frac{1728\ \text{in}^3}{231\ \text{in}^3} = 7.480519\ \text{US gal per ft}^3$

The form carries the exact 1,728/231 gallons-per-cubic-foot ratio and rounds only displayed results.

Formula used by the calculator

To convert gallons to cubic feet, divide by the gallons that fit in one cubic foot:

$\text{cubic feet} = \frac{\text{US gallons}}{7.48051948051948}$

The reverse relationship is:

$\text{US gallons} = \text{cubic feet} \times 7.48051948051948$

The calculator also reports:

$\text{cubic inches} = \text{cubic feet} \times 1728$

$\text{liters} = \text{US gallons} \times 3.785411784$

Conversion example using the stated method

For a 10 US gal container, the primary calculation is:

$\text{cubic feet} = 10 \times \frac{231}{1728} = 1.3368055555555556$

The displayed primary result is 1.336806 ft³. The supporting items show about 2310 in³, 37.8541 L, 0.037854 m³, and 7.48051948051948 gal/ft³. The unrounded cubic-meter value is 0.03785411784 m³. Those values are consistent: 10 gallons times 231 cubic inches per gallon gives 2,310 cubic inches, and 2,310 divided by 1,728 gives the same cubic-foot result after rounding.

Reference table

Tank and space examples

Aquariums are often sold by gallons, while stands, cabinets, and shipping spaces may be discussed in cubic feet. Convert the water volume here, then leave margin for glass thickness, substrate, rock, decorations, and water below the rim. Rain barrels and drums are similar: a 55-gallon drum occupies a little over 7.35 cubic feet of liquid volume, but the physical footprint can be larger because of wall shape and headspace.

Sump pits, planters, and bins usually start from dimensions. For a rectangular shape, multiply length × width × depth in feet to get cubic feet, then multiply by 7.48051948051948 to estimate gallons. This calculator handles the opposite direction when the known value is gallons. For soil or mulch, remember that dry bulk materials settle and are not liquid gallons; use a material-specific estimate before ordering.

Equipment clearances are another reason to convert. A pump manual may state a minimum basin volume in gallons, while a contractor may describe the available pit in cubic feet. Converting the gallon requirement lets both notes sit in the same unit before you decide whether the space has enough reserve capacity.

Pitfalls to avoid

• Do not confuse cubic feet with square feet. Area needs a depth before it becomes volume.
• Do not enter imperial gallons. This page follows the US liquid gallon defined as 231 cubic inches.
• Do not assume a nominal tank size equals usable volume. Overflow height, fittings, and internal parts matter.
• Do not convert gallons to weight without density; water, oil, fuel, and brine differ.
• Do not mix rounded table values repeatedly. For planning several containers, add gallons first and convert once.

Sources

• NIST, HB 44 (2024), Appendix C, printed page C-6 (PDF page 6), “Units of Volume” and “Units of Liquid Volume” — 1 ft³ = 1,728 in³ and 1 US liquid gallon = 231 in³.
• NIST, SI Units — metric unit context for liters and cubic meters.
• BIPM, SI base units — international SI reference used for metric measurements.