Gallons to Liters Calculator

How the US gallons to liters conversion works

The calculator multiplies the US liquid gallon input by the exact factor 3.785411784 to produce liters. That factor is derived from the definition: one US liquid gallon equals exactly 231 cubic inches, and one cubic inch equals exactly 16.387064 mL, so 1 US gal = 231 × 16.387064 mL = 3,785.411784 mL = 3.785411784 L. The secondary outputs — imperial gallons, US quarts, and cubic feet — are all derived from the same input using fixed, exact factors.

The exact conversion factor

The US liquid gallon is defined as 231 cubic inches. The inch was fixed at exactly 25.4 mm in 1959, making the cubic inch exactly 16.387064 mL. Multiplying: 231 × 16.387064 = 3,785.411784 mL = 3.785411784 L. This is a defined constant, not a measured one. The calculator displays liters to two decimal places (3.79 L for 1 US gal), but the arithmetic uses the full precision factor.

US gallon vs. imperial (UK) gallon — a key distinction

The US gallon and the imperial (UK) gallon are different units. One US gallon is 3.785411784 liters; one imperial gallon is 4.54609 liters — about 20% larger. A product labeled in imperial gallons holds more than the same number of US gallons. The calculator shows imperial gallons as a secondary output so the two can be compared directly: 1 US gal = 0.833 UK gal. This distinction matters when reading UK equipment datasheets, Canadian specifications, or products imported from Commonwealth countries.

Worked examples

One US gallon equals 3.79 liters, 0.833 imperial gallons, 4.00 US quarts, and 0.1337 cubic feet. Ten US gallons equal 37.85 liters, 8.327 imperial gallons, 40.00 quarts, and 1.3368 cubic feet. Five US gallons equal 18.93 liters, 4.163 imperial gallons, 20.00 quarts, and 0.6684 cubic feet.

Where US gallons appear in construction and engineering

Water heaters in the US are rated and sold by storage capacity in gallons — a 40-gallon or 50-gallon tank is the standard residential size. Hot-water demand calculations and energy-efficiency ratings use gallons per hour. Irrigation systems are designed in gallons per minute (GPM) for pump sizing and pipe flow. Concrete mixing water, grout mix ratios, and waterproofing product coverage rates are sometimes stated in gallons per square foot or gallons per bag. When working with metric-spec equipment or international product documentation, those gallon figures convert to liters using this factor.

Tank and container capacity

Rainwater harvesting tanks, cisterns, and retention basins are commonly sized in gallons in the US. A 500-gallon cistern is 1,892.7 liters; a 1,000-gallon tank is 3,785.4 liters. Septic tanks rated in gallons convert to cubic meters for permitting documents that require metric volumes: divide the liter result by 1,000, or divide gallons directly by 264.172.

US quarts and the gallon subdivision

One US liquid gallon equals exactly 4 US quarts, 8 US pints, or 128 US fluid ounces. These are exact subdivisions defined by the same 231-cubic-inch base. When a product data sheet states a coverage rate or mixing ratio in quarts, multiplying by 4 converts to gallons, and then multiplying by 3.785411784 converts to liters.

Cubic feet from gallons

One cubic foot equals exactly 1,728 cubic inches. Since one US gallon is 231 cubic inches, one cubic foot holds 1,728 ÷ 231 = 7.48052 US gallons, and equivalently one gallon is 1 ÷ 7.48052 = 0.133681 cubic feet. This relationship connects the gallon to structural volume calculations: a 4 ft × 4 ft × 1 ft retention basin holds 16 ft³ × 7.48052 = 119.7 gallons = 453 liters.

Precision and rounding

Liters are displayed to two decimal places (resolution of 0.01 L = 10 mL), appropriate for tank sizing and fluid volumes at the scale of residential and commercial construction. Imperial gallons are shown to three decimal places to make the US/UK difference visible even at small volumes. US quarts are shown to two decimal places and cubic feet to four.

Using this alongside other BuildMetricLab tools

The liter result connects directly to metric pump-flow calculations, tank volume calculations, and irrigation system sizing. For larger volumetric conversions the cubic yards to cubic meters calculator handles concrete and aggregate volumes. All BuildMetricLab tools run entirely in the browser — no sign-up, no data sent anywhere, and the formula is shown on the page so the math can be audited.