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Litres vs. Gallons

One litre, two different gallons — know which one you are dealing with.

1 US gallon = 3.785 L. 1 UK gallon = 4.546 L. They are NOT the same size.

The gallon is two different sizes depending on where you are. A US gallon is about 20% smaller than a UK gallon — so "fuel economy in mpg" or "tank capacity in gallons" mean different things in the two countries.

Part of: Unit Conversion Tools

Quick answer

1 US gallon = 3.785 L. 1 UK gallon = 4.546 L. They are NOT the same size.

What you are trying to do
One litre, two different gallons — know which one you are dealing with.
Best next step
Volume Converter
Limit to remember
Treat this as a practical aid for the task, not a replacement for professional judgment.

Key points

  • ▸ 1 US gallon = 3.785 litres (128 US fluid ounces).
  • ▸ 1 UK (imperial) gallon = 4.546 litres (160 UK fluid ounces).
  • ▸ 1 UK gallon ≈ 1.2 US gallons. That is a ~20% difference.
  • ▸ A UK fluid ounce and a US fluid ounce are also different — UK fl oz is slightly smaller.
  • ▸ Fuel economy: 30 mpg (UK) ≈ 25 mpg (US). Always check which gallon.

Examples

  • Fuel tank: 15 US gal
    15 × 3.785 = 56.8 L.
  • Milk jug: 1 UK gallon
    4.546 L ≈ 4.55 L. Supermarket 4-pint jug = 2.27 L.
  • Recipe: "one gallon"
    American recipe = 3.785 L. British recipe = 4.546 L. Assume US unless stated otherwise in modern cookbooks.

When to use which tool

Related

Frequently asked questions

› Why are US and UK gallons different? Troubleshooting

Historical accident. The UK imperial gallon was defined in 1824 based on 10 lb of water. The US kept the older English wine gallon (231 cubic inches). Neither country has changed since.

› Which gallon do Canada and Australia use?

Both use metric officially. Canada historically used UK gallons; Australia too. But for fuel, anything pre-metric in those countries is ambiguous — check.

› How accurate are online calculators and converters? Trust & accuracy

Online calculators are only as accurate as the numbers, units, assumptions, and rounding choices you enter. Recheck the input values first, then compare the formula against your real situation. For legal, tax, medical, financial, or professional decisions, treat the result as a planning estimate, not advice.

› What inputs should I double-check first? Troubleshooting

Double-check units, dates, percentages, decimal placement, and whether the input is before-tax, after-tax, gross, net, original, or final. Most calculator mistakes come from feeding the right formula the wrong base. If the result feels off, rebuild it from a simple worked example.

› Why do two calculators sometimes give different answers? Comparison

Two calculators may round at different steps, use different defaults, or interpret the same label differently. Percent, time, finance, and unit tools are especially sensitive to basis and rounding rules. Compare the formula, not just the final number, before deciding which result to trust.