How Many Liters in a Gallon? The Complete Guide (US & UK)

Quick Answer — TL;DR

1 US gallon = 3.785411784 liters exactly; 1 UK imperial gallon = 4.54609 liters exactly. The imperial gallon is about 20.095% larger. To convert, multiply gallons by 3.78541 (US) or 4.54609 (UK); to go liters→gallons, divide. Example: 10 US gal = 37.85 L; 10 UK gal = 45.46 L. Guide includes 5 examples, mistakes, and FAQs.

The question "How many liters in a gallon?" is one of the most common conversion queries online. But the answer isn't always straightforward because there are two different types of gallons used around the world.

US Gallon vs UK Imperial Gallon

The United States uses the US gallon (3.78541 L), while the United Kingdom and many Commonwealth countries use the imperial gallon (4.54609 L). This difference dates back to historical measurement standards.

Quick Answer: Liters per Gallon

1 US gallon = 3.785 liters
1 UK (imperial) gallon = 4.546 liters

This means the UK gallon is about 20% larger than the US gallon — a critical difference when comparing fuel economy, cooking recipes, or any liquid measurements.

Gallon to Liter Conversion Table

1 gal (US) = 3.785 L | 1 gal (UK) = 4.546 L
2 gal (US) = 7.571 L | 2 gal (UK) = 9.092 L
5 gal (US) = 18.927 L | 5 gal (UK) = 22.730 L
10 gal (US) = 37.854 L | 10 gal (UK) = 45.461 L

How to Convert Gallons to Liters

To convert US gallons to liters: multiply by 3.785. To convert UK gallons to liters: multiply by 4.546. Going the other way? Divide liters by 3.785 (US) or 4.546 (UK). Use our free volume converter above for instant, accurate results.

Why Knowing the Difference Matters

Using the wrong gallon type can lead to significant errors. For example, if a UK recipe calls for 5 imperial gallons of water and you mistakenly use US gallons, you would be off by nearly 4 liters. This is especially critical in cooking, automotive fuel calculations, and industrial chemical mixing.

Exact Definitions, Formulas & Sources

The US gallon is defined as 231 cubic inches exactly (NIST Handbook 44, 1 in = 2.54 cm exactly, so 231 in³ = 3.785411784 L exactly). The UK imperial gallon is defined as the volume of 10 pounds of distilled water at 62 °F and 30 inHg, standardized to 4.54609 L exactly (UK Weights and Measures Act 1985). Therefore 1 L = 0.264172052 US gal = 0.219969248 UK gal. 1 US gal = 0.83267384 UK gal. ISO 80000-4 and NIST SP 811 list these as exact conversion factors for trade.

Sources: NIST Handbook 44 §4.45, UK National Physical Laboratory (NPL), BIPM SI (liter = 1 dm³ = 0.001 m³), ISO 80000-4:2019. Since 1964, the liter is exactly 1 cubic decimeter, not the old water-mass definition.

Worked Examples (5-step table)

Worked examples — see the calculation shown step by step:

• Example 1 — US fuel: 15 US gal → L: 15×3.78541=56.781 L. Reverse: 50 L → US gal: 50÷3.78541=13.209 gal.
• Example 2 — UK fuel: 40 UK gal → L: 40×4.54609=181.844 L. Same 40 US gal would be 151.416 L — 30 L less, critical for aircraft fueling.
• Example 3 — Cooking: US recipe 1 US cup = 1/16 US gal = 0.236588 L; UK cup is not standardized (often 284 mL half-pint). Converting 4 US quarts (1 US gal) to UK pints: 3.785 L ÷ 0.56826 L/pint = 6.66 UK pints vs. 8 US pints.
• Example 4 — Aquaria: 55 US gal tank = 208.2 L; advertised as '55 gal' in UK would be 250 L — verify which gallon at purchase.
• Example 5 — Fuel economy: 30 MPG (US) = 30 miles per 3.785 L; 30 MPG (UK) = 30 miles per 4.546 L. Hence 30 MPG (UK) = 36.0 MPG (US) — always note the gallon type.

Common Mistakes and How to Fix Them

• Mistake: Assuming 'gallon' is universal. Fix: Always write 'US gallon' or 'imperial gallon'. In e-commerce, check seller location: US listings use 3.785 L, UK use 4.546 L.
• Mistake: Mixing fluid gallon with dry gallon. Fix: The US dry gallon (4.40488 L, 268.8 in³) is rare (grain), not for liquids. Liquids use the 231 in³ fluid gallon.
• Mistake: Rounding 3.785 to 3.8 and compounding. Fix: For 100 gallons, 0.015 L/gal error = 1.5 L. Use 3.78541 for invoices and chemistry; 3.79 is fine for estimates.
• Mistake: Confusing liter with kilogram. Fix: 1 liter of water ≈ 1 kg at 4 °C, but oil (~0.92 kg/L) and gasoline (~0.74 kg/L) are less; do not convert volume to weight without density.

Frequently Asked Questions (FAQ)

Why are US and UK gallons different?

Both descend from medieval wine and ale gallons. In 1824 Britain unified them to the imperial gallon (277.42 in³, now 4.54609 L). The US kept the older Queen Anne wine gallon (231 in³, now 3.78541 L) after independence. The 1824 split persists; NIST and NPL maintain the two exact values today.

How many liters are in a half-gallon or quart?

US: 0.5 gal = 1.89271 L; 1 US quart = 1/4 US gal = 0.946353 L; 1 US pint = 0.473176 L; 1 US fluid ounce = 29.5735 mL. UK: 0.5 imperial gal = 2.27305 L; 1 imperial quart = 1.13652 L; 1 imperial pint = 0.568261 L; 1 imperial fluid ounce = 28.4131 mL. Note US and UK pints/ounces also differ.

Which gallon should I use for fuel economy comparisons worldwide?

Standardize to liters per 100 km (L/100km) for global comparison, or convert all MPG to one gallon type: MPG (US) = MPG (UK) × 0.83267. Example: 50 MPG (UK) = 41.6 MPG (US). The EU, Canada, and Australia legally require L/100km; the US uses MPG (US); the UK still advertises MPG (UK) though fuel is sold in liters.

How to Convert Gallons ↔ Liters in 3 Steps

1. Step 1: Confirm the gallon type: US (3.78541 L) or imperial (4.54609 L). Check the product origin or ask the seller.
2. Step 2: Multiply gallons by the factor to get liters, or divide liters by the factor to get gallons. Use the converter above for instant exact results.
3. Step 3: Verify: 1 US gal ≈ 3.79 L, 1 imperial gal ≈ 4.55 L. For large batches, keep 5 significant digits to avoid cumulative error.

Try the Converter & Keep Reading

Try it yourself: open the Volume Converter or Fuel Consumption Converter on OmniConverter for instant, high-precision results. For deeper reading, see our ultimate volume conversion guide — it pairs perfectly with this guide.

Sources: BIPM SI Brochure 9th edition (2019), NIST SP 811 Guide for the Use of the SI, ISO 80000 series for quantities and units. All exact factors are per international agreement.