How Many Litres in a Gallon? US vs UK Complete Guide

Need to convert how many litres in a gallon? How Many Litres in a Gallon? US vs UK Complete Guide - OmniConverter does it instantly: type once, see every unit, exact BIPM/NIST factors, no sign-up. Try our Volume Converter free - private, in your browser, on any device.

Quick Answer

Quick Answer

US gallon = 3.78541 L, UK gallon = 4.54609 L, difference 0.76068 L (20%).

Example: 5 US gal = 18.93 L, 5 UK gal = 22.73 L.

Why this conversion matters

Every day you see how many litres in a gallon - on shopping labels, car dashboards, recipes, or work specs. Getting it wrong costs money or time. In the UK, mixing US and UK gallons means 20% fuel error. Mixing stone and kg means wrong clothing size. Mixing 1024 and 1000 means missing phone storage. Our Volume converter uses exact BIPM/NIST factors, not rounded estimates, so you get the honest answer. Unlike cloud tools, OmniConverter runs 100% in your browser - your values never leave your device. Private, fast, on any phone.

Where You'll Use This

• Road trip: 300 miles at 40 MPG UK = 34.1 litres, same MPG US = 28.4 litres
• US recipe 1 gallon = 16 cups (3.785 L), UK 1 gallon = 16 cups but 4.546 L - cups differ too
• Ferry fuel: Calais to Dover - check if station quotes UK or US gallons

How to use the converter in 3 steps

1. Step 1: Select your From and To units (e.g., stone to kg).
2. Step 2: Type the amount - every unit updates as you type.
3. Step 3: Copy with the copy icon.

Common mistakes to avoid

• Mixing US vs UK systems - gallon, pint, and stone differ between US and UK. Always check your source system before converting.
• Rounding too early - keep the full factor (like 6.35029, not 6.35) until the final display, then round to 2 decimals for daily use.
• Using 1000 instead of 1024 for digital storage - RAM and files use 1024 (binary), drive makers use 1000 (decimal). Use 1024 for exact.

Always double-check your source system and use the exact factor from BIPM or NIST for critical work.

Internal guides & tools

Explore more: Length Converter, Weight Converter, Volume Converter, Temperature Converter and our OmniCalculator suite for BMI, body fat and calorie.

Sources & standards

BIPM - SI Brochure 9th ed. - bipm.org

NIST SP 811 - Guide for SI - nist.gov

Wikipedia - how many litres in a gallon

UK Legislation - Weights and Measures Act 1985 - legislation.gov.uk

FAQ - People also ask

What is the exact formula for how many litres in a gallon?

See quick answer above - exact factor from BIPM/NIST. For how many litres in a gallon, keep full precision until final display, then round to 2 decimals for daily use.

How do I how many litres in a gallon without calculator?

Use our free converter at omniconverter.org/volume?from=gallon-us&to=liter - type value, get instant answer, copy. Works offline after load, no sign-up.

Why does how many litres in a gallon matter?

It affects shopping, travel, recipes, health, or work specs daily. Wrong conversion = wrong dose, wrong size, or overpaying. Use exact factors.