About

Volume conversion between metric and imperial systems is a frequent source of error in international logistics, automotive specifications, and chemical trading. The ambiguity of the term gallon is the primary risk factor. A US Liquid Gallon differs significantly from an Imperial (UK) Gallon, creating a discrepancy of approximately 20%.

This tool enforces a distinction between the two standards to prevent costly miscalculations. It provides decimal precision for engineering applications and a mixed-unit format (Gallons and Fluid Ounces) for practical usage in bottling or tank gauging.

Formulas

The conversion logic depends strictly on the target system selected. The definitions are exact constants defined by NIST and the Weights and Measures Act.

For US Liquid Gallons:

V_gal(US)1 = V_L3.785411784

For Imperial (UK) Gallons:

V_gal(UK)1 = V_L4.54609

To calculate the mixed unit remainder (Fluid Ounces), we use the following modulus logic:

R_oz = {

(V_gal − floor(V_gal)) × 128 if US(V_gal − floor(V_gal)) × 160 if UK

Reference Data

Liters (L)	US Gallons (US gal)	Imperial Gallons (Imp gal)
1	0.264	0.220
3.785	1.000	0.833
4.546	1.201	1.000
10	2.642	2.200
20	5.283	4.400
50	13.209	10.998
100	26.417	21.997
159 (1 Barrel)	42.004	34.975

Frequently Asked Questions

The US Liquid Gallon is based on the pre-19th century British wine gallon, defined as 231 cubic inches. The Imperial Gallon was established in 1824 by the British Weights and Measures Act, based on the volume of 10 pounds of water at 62°F. They are distinct units; confusing them leads to a ~20% volume error.

No. This calculator focuses specifically on liquid volume. The US Dry Gallon (approx 4.405 L) is a rarely used unit primarily for agricultural commodities like grains or berries and is not covered here.

We use the exact definition factors. 1 US Gallon is exactly 3.785411784 Liters. 1 Imperial Gallon is exactly 4.54609 Liters. Calculations are performed using double-precision floating-point arithmetic.

A US Gallon contains 128 US fluid ounces. An Imperial Gallon contains 160 Imperial fluid ounces. Note that the fluid ounce unit itself also differs slightly in size between the two systems.