How to Convert Gallons to Liters

4 min read•June 1, 2025•Reviewed: June 1, 2026

✓Reviewed by Apex Conversion Editorial Team · Last reviewed June 1, 2026

To convert US gallons to liters, multiply by 3.78541. For a quick estimate, multiply by 3.8 — accurate within 0.4%. The conversion is most commonly needed for fuel comparisons, bulk water containers, and vehicle fuel tank capacities.

The most important thing to check first: US gallon (3.785 L) or UK/Imperial gallon (4.546 L)? If a product, recipe, or specification comes from the UK, use 4.546; for US products, use 3.785.

Step-by-Step Method

Step 1: Confirm whether you have US gallons or Imperial gallons. Step 2: Multiply by 3.78541 (US) or 4.54609 (Imperial). Step 3: Round to two decimal places for everyday use.

Example — Convert 12 US gallons to liters: 12 × 3.78541 = 45.42 L. Quick estimate: 12 × 3.8 = 45.6 L — within 0.4% of exact.

Worked Examples

Fuel tank: 16 gal
  16 × 3.78541 = 60.57 L  (shortcut: 16 × 3.8 = 60.8 L)

Water: 5 gal jug
  5 × 3.78541 = 18.93 L

Aquarium: 55 gal
  55 × 3.78541 = 208.20 L

Bucket: 2.5 gal
  2.5 × 3.78541 = 9.46 L

Fuel Economy Applications

Fuel prices in metric countries are given per liter; US prices are per gallon. To compare: multiply the US price per gallon by 0.264 to get price per liter, or divide by 3.785. Example: $3.50/gal ÷ 3.785 = $0.92/liter.

Fuel efficiency: US cars are rated in mpg (miles per gallon). International cars use L/100km. To convert mpg to L/100km: divide 235.214 by the mpg value. Example: 30 mpg = 235.214 ÷ 30 = 7.84 L/100km.

Quick Tips

✓
Multiply by 3.8 for a fast estimate — close enough for fuel, pool, and tank sizing.
✓
1 gallon ≈ 3.8 L — the key anchor for gas station price comparisons.
✓
5 gallons ≈ 19 L — the standard water jug size.
✓
Always verify US vs. Imperial gallon when working with UK specifications.