How many litres are in a US gallon?

A US gallon is exactly 3.785411784 litres, which is 3785.41 mL or 128 US fluid ounces. To convert US gallons to litres, multiply by 3.785411784; to go from litres to US gallons, multiply by 0.264172. Note the UK gallon is different — 4.54609 litres.

What's the difference between US and UK gallons?

They differ by about 20%: a US gallon is 3.785 litres while a UK (imperial) gallon is 4.546 litres. So 1 UK gallon = 1.20095 US gallons. US and UK fluid ounces also differ. Using the wrong one silently corrupts results, so always confirm which system a recipe or spec means.

How do I convert millilitres to fluid ounces?

Divide millilitres by 29.5735 for US fluid ounces (1 US fl oz = 29.5735 mL). So 500 mL ≈ 16.907 US fl oz. A litre is 33.814 US fluid ounces. UK fluid ounces are slightly smaller at 28.413 mL, so check which you need.

Is this the same as a volume calculator?

No. This tool converts a volume between units (litres, gallons, mL, cups). To work out the volume of a 3D shape — a box, cylinder, sphere or cone — from its dimensions, use the separate Volume Calculator. The two are complementary: compute the volume of a tank, then convert it from cubic metres to gallons here.

How many mL in a cup?

A US customary cup is 236.588 mL (this converter uses the US cup). The US 'legal' cup used on nutrition labels is 240 mL, and a metric cup is 250 mL, so cups vary by region. For precise cooking, weigh ingredients where possible. 1 US cup = 8 US fluid ounces.

Volume Converter — litres, gallons, mL, m³, cups & fl oz

From	Equals
1 litre	0.264172 US gal · 33.814 US fl oz
1 US gallon	3.785412 L · 128 US fl oz
1 UK gallon	4.54609 L · 1.20095 US gal
1 m³	1000 L · 264.172 US gal

A volume converter moves a capacity between metric units (litres, millilitres, cubic metres) and US/UK units (gallons, fluid ounces, cups). It converts your value into a base unit — litres — and back out. The one thing to watch is that the US gallon and UK gallon differ by about 20% (3.785 vs 4.546 litres), so always pick the right system. This tool converts units; to find the volume of a 3D shape, use the Volume Calculator.

Reviewed: June 20, 2026 · Author: Naveen P N, Founder — AI Calculator · Verified against: NIST volume factors, recomputed in code.

How the conversion works

Via a base unit

result = value × factor(from) ÷ factor(to) (factor = litres per unit)

Key factors

1 mL = 0.001 L · 1 m³ = 1000 L · 1 US gal = 3.785412 L · 1 UK gal = 4.54609 L · 1 US fl oz = 0.0295735 L

Every unit equals a fixed number of litres: a US gallon is 3.785412 L, a UK gallon 4.54609 L, a US fluid ounce 0.0295735 L, and a US cup 0.2365882 L. Multiply your value by the "from" unit's litres-per-unit to reach litres, then divide by the "to" unit's. Because there are two gallons (and two fluid ounces) in common use, the converter labels US and UK units separately so you never mix them by accident.

Worked example — 1 US gallon in other units

Scenario: convert 1 US gallon to other volume units.

To litres

1 × 3.785412 = 3.785412 L

To US fluid ounces

3.785412 ÷ 0.0295735 = 128 US fl oz

To UK gallons

3.785412 ÷ 4.54609 = 0.832674 UK gal

One US gallon is 3.785412 litres, 128 US fluid ounces, or 0.832674 UK gallons. The everyday cases follow the same rule: 1 litre is 0.264172 US gallons (33.814 US fl oz), 1 m³ is 1000 litres (264.172 US gallons), and 1 UK gallon is 1.20095 US gallons. The converter shows your value in every supported unit at once.

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Frequently Asked Questions

Litres in a US gallon?⌄

3.785412 L (128 US fl oz). UK gallon is bigger: 4.54609 L.

US vs UK gallon?⌄

~20% apart: US 3.785 L, UK 4.546 L. 1 UK gal = 1.20095 US gal.

mL to fluid ounces?⌄

÷ 29.5735 for US fl oz. 1 L = 33.814 US fl oz.

Same as a volume calculator?⌄

No — this converts units; the Volume Calculator finds a shape's volume.

mL in a cup?⌄

US customary cup = 236.588 mL (= 8 US fl oz). Metric cup is 250 mL.

Volume Converter

Volume conversion — Quick answer