Gallons to Liters Converter (US & UK gallon) 🌎

How It Is Calculated

Both conversions use the exact factors adopted by the international yard and pound agreement (1959) and codified by NIST:

US liquid gallon → liters:
  L = gal_US × 3.785411784

Imperial (UK) gallon → liters:
  L = gal_UK × 4.54609

Liters → US liquid gallon:
  gal_US = L ÷ 3.785411784

Liters → Imperial (UK) gallon:
  gal_UK = L ÷ 4.54609

US gallon → Imperial gallon:
  gal_UK = gal_US × 0.832674

Imperial gallon → US gallon:
  gal_US = gal_UK × 1.200950

> Why are the factors exact? The liter is defined as exactly 1 cubic decimeter (1 dm³). The US gallon is defined as exactly 231 in³, and 1 inch = 25.4 mm exactly, giving the exact 3.785411784 L figure. The Imperial gallon was redefined in 1985 as exactly 4.54609 L by UK statute.

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Gallons to Liters Quick Reference Table

US Gallons	UK Gallons	Liters
0.25	0.208	0.946
0.5	0.416	1.893
1	0.833	3.785
2	1.665	7.571
5	4.163	18.927
10	8.327	37.854
15	12.490	56.781
20	16.653	75.708
25	20.817	94.635
30	24.980	113.562
50	41.633	189.271
55	45.796	208.198
100	83.267	378.541

> All values rounded to 3 decimal places for readability; the converter uses full NIST precision.

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Practical Examples

Example 1 – Fuel tank for a road trip

A US pickup truck has a 26-gallon (US) tank. A driver crossing into Canada wants to know the capacity in liters:

26 × 3.785411784 = 98.421 L

The tank holds 98.4 liters. At CAD $1.60/L, a full fill-up costs approximately CAD $157.47.

Example 2 – British homebrew recipe

A classic British ale recipe calls for 5 Imperial gallons of water. The American brewer's kettle is marked in liters:

5 × 4.54609 = 22.730 L

The brewer needs 22.73 liters — notably more than the 18.93 L a US-gallon interpretation would give, a difference of nearly 3.8 liters that would throw off malt concentration significantly.

Example 3 – Industrial chemical order

A factory orders 200 US gallons of solvent. The EU supplier invoices in liters:

200 × 3.785411784 = 757.082 L

The order corresponds to 757.08 liters. Using the UK gallon factor by mistake would calculate 909.2 L — an over-order of more than 152 liters.

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Common Mistakes

1. Assuming all gallons are equal. The US and UK gallon differ by ~20.1%. Using the wrong factor in fuel calculations leads to errors of roughly 1 liter per 5 liters converted — significant at scale.

2. Confusing the US liquid gallon with the US dry gallon. The US dry gallon (≈ 4.40488 L, used for grain and produce) is legally distinct and larger than the liquid gallon. This converter handles the liquid gallon, which is the standard for fuel, beverages, and most consumer goods.

3. Rounding the conversion factor to 3.78 or 4.55. Using 3.78 instead of 3.785411784 introduces an error of ~0.14% per conversion. Over 10,000 gallons (e.g., a fuel depot), that shortfall is ~14 liters — enough to matter for billing or compliance.

4. Applying US-gallon MPG directly to liters-per-100km. The formula is L/100km = 235.214 ÷ MPG_US, not a simple multiplication. Using the liters-per-gallon factor directly without the distance component gives a dimensionally incorrect result.

5. Ignoring temperature effects in legal metrology. For trade purposes (fuel dispensing), volumes are often corrected to 15 °C (60 °F). The raw gallon-to-liter conversion does not include temperature correction; always check whether a thermal volume correction is required for official or commercial use.