Gallon to Liters: Convert US Gallons to Litres
Convert gallon to liters: one US gallon equals 3.785 liters. Learn the exact factor, how it is used for fuel and jugs, and common gallon-to-liter values.
Why Gallons to Liters Comes Up
The gallon is the US unit for fuel, milk jugs, and paint, while liters are used almost everywhere else. Anyone filling a tank or buying a jug abroad needs the gallon-to-liter figure.
One US gallon equals 3.785411784 liters. Our gallon to liters converter returns it exactly; 3.785 L is the rounded value you will see.
The Gallon to Liters Formula
The US liquid gallon is defined as exactly 231 cubic inches, which works out to 3.785411784 liters. Multiply gallons by 3.785411784 to get liters.
The Exact Calculation
For 1 gallon: 1 × 3.785411784 = 3.785411784 L, rounded to 3.785 L. For 5 gallons: 5 × 3.785411784 = 18.927 L, close to a typical fuel can.
The factor is exact by definition of the US gallon, so the only rounding is for display. The imperial (UK) gallon is larger at 4.546 L; use 3.785 L for US gallons.
Why 3.785 Liters
Because a gallon is 4 quarts, a quart is 2 pints, a pint is 2 cups, and a cup is 236.588 ml, the chain gives 16 cups per gallon, or 16 × 236.588 = 3784.9 ml = 3.785 L. The number comes directly from the cup definition.
What the Numbers Look Like
Everyday sizes: a 1-gallon milk jug is 3.785 L; a 2.5-gallon watering can is about 9.46 L; a 5-gallon fuel can is 18.93 L; a 55-gallon drum is about 208 L.
At the pump, US gas prices are per gallon, but many world maps show fuel per liter, so the conversion helps compare costs while traveling.
Gallon to Liters Compared With Nearby Volumes
Reference points: 0.5 gal = 1.893 L, 2 gal = 7.571 L, 10 gal = 37.854 L. Each gallon adds 3.785 L, a steady, predictable step.
For the reverse direction, our guide to liters to gallons shows how metric jug sizes map back to gallons.
When You Need Gallons in Liters
The conversion is most useful for fuel and bulk liquids. A "10-gallon tank" is about 37.85 L; a recipe or cleaning mix given "per gallon" becomes a per-3.785-L figure in metric.
It also helps when buying imported containers sized in liters and you want to know the US gallon equivalent for storage or dosing.
Frequently Asked Questions
How many liters is 1 gallon?
1 US gallon equals exactly 3.785411784 L, normally rounded to 3.785 L.
How do I convert gallons to liters?
Multiply gallons by 3.785411784. For 5 gallons: 5 × 3.7854 = 18.927 L.
Is a US gallon the same as a UK gallon?
No. The US gallon is 3.785 L; the imperial UK gallon is 4.546 L. Use 3.785 L for US gallons.
How many liters is a 55-gallon drum?
55 US gallons equals about 208.2 L (55 × 3.7854).
How many gallons is 20 liters?
20 L equals about 5.283 US gallons (20 / 3.7854).
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US Gallons to Liters Converter
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Quick Summary
1 US gallon equals 3.785 L. Multiply gallons by 3.785411784 (the exact liters per US gallon): 1 × 3.7854 = 3.785 L. The UK gallon is larger at 4.546 L.
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Disclaimer
Unit conversions on this site use internationally recognized, fixed conversion factors (for example, 1 inch = 2.54 cm, 1 pound = 0.45359237 kg, 1 °F = (°C × 9/5) + 32). They are provided for general, informational, and educational use. For applications where accuracy is critical — such as medical dosing, engineering, scientific research, trade, or legal compliance — always verify results against authoritative sources such as the U.S. National Institute of Standards and Technology (NIST) and the official International System of Units (SI) brochure, and follow any applicable local standards.
Exact Constants & Authoritative Sources
Every conversion on this page uses the fixed, internationally agreed constants below — drawn from NIST and the SI Brochure. No values are estimated or rounded as if exact. See the full list on our Sources & Standards page.
- EXACT1 US gallon (gal) = 3.785411784 litres (exact, 231 in³)
- EXACT1 US fluid ounce (fl oz) = 29.5735295625 mL (exact, 1/128 gal)
- EXACT1 US cup = 236.5882365 mL (exact, 8 fl oz)
- EXACT1 US pint (pt) = 473.176473 mL (exact, 16 fl oz)
- EXACT1 US quart (qt) = 946.352946 mL (exact, 32 fl oz)
- EXACT1 litre (L) = 1000 millilitres (definition)
Common Pitfalls & How to Avoid Them
US vs. Imperial (UK) cups
A US cup is 236.59 mL, but a UK/metric cup is 250 mL and an Imperial cup is ~284 mL. Recipes from different countries are not interchangeable drop-in.
Fluid ounce is volume, not mass
A US fl oz is 29.57 mL of volume. 1 fl oz of water ≈ 29.57 g, but 1 fl oz of honey or oil weighs more. Do not treat fluid ounces as grams.
Teaspoon/tablespoon sizes differ
1 US tbsp = 14.7868 mL; 1 US tsp = 4.92892 mL. Metric measuring spoons are 15 mL and 5 mL — close but not exact; for baking precision use weighed grams.
A unit-conversion reference site has no manufacturer-specific or device calibration parameters, so "layered tuning" does not apply here. The only real error-handling is input validation: the converter rejects non-numeric, empty, or out-of-range entries and shows a clear message, then falls back to exact constants above. No estimated or rounded figures are ever presented as exact.
Authoritative sources for this page
- NIST (U.S. National Institute of Standards and Technology) — NIST SP 330 — The International System of Units (SI), 2019 edition
- BIPM (International Bureau of Weights and Measures) — SI Brochure — The International System of Units (9th edition)
Last Updated 2026 | This article was reviewed for accuracy