Gallons to Liters Converter

A US gallon is exactly 3.785411784 liters:

liters = US gallons × 3.785411784

The odd factor is historical. The US gallon was fixed as 231 cubic inches — the volume of an old English wine gallon — while Britain redefined its own gallon in 1824 as the volume of ten pounds of water, giving 4.54609 L. The two have been 20% apart ever since.

So an American "gallon of gas" is 3.785 L, and a British "gallon" in an older context is 4.546 L. This converter uses the US gallon.

Common volumes:

• 1 gal of milk → 3.79 L
• 5 gal (a US bucket, a water-cooler bottle) → 18.93 L
• 20 gal aquarium → 75.71 L
• 55 gal drum → 208.20 L — the standard oil drum, usually described as a 200 L drum outside the US, which is a different drum
• 1 barrel of oil is 42 US gallons → 158.99 L

Paint is the domestic case where the difference bites. A US gallon covers roughly 350–400 sq ft; a 5 L European tin covers a comparable area but is not the same quantity. Buying "a gallon" of paint in Europe gets you 5 L, which is 32% more than a US gallon — fine for coverage, misleading for cost comparison.

For a mental estimate, multiply by 4 and take off 5%: 5 gal → 20 → 19 L, against a true 18.93.