Volume Converter
Volume carries a trap the other conversions do not: several units share a name across the Atlantic while holding different amounts. This converter uses US liquid measures, and the notes below give the Imperial equivalents.
Formula
litres = value × factor for the unit
- 1 litre = 1,000 cm³
- US and Imperial units of the same name differ
5 US gallons: 5 × 3.785 = 18.93 litres
The Same Word, Two Different Sizes
A gallon, a pint and a fluid ounce all mean one thing in the United States and another in the UK. The difference is large enough to ruin a recipe or misprice a fuel comparison:
- Gallon: US 3.785 L, Imperial 4.546 L — the Imperial gallon is 20% larger
- Pint: US 473 mL, Imperial 568 mL
- Fluid ounce: US 29.57 mL, Imperial 28.41 mL — here the US one is larger
The fluid ounce reversing direction is not a typo. An Imperial pint holds 20 fluid ounces and a US pint holds 16, so the pints and the ounces scale differently.
A cup adds a third variant: the US cup is 236.6 mL, while the metric cup used in Australian and much modern recipe writing is a round 250 mL.
Litres, Millilitres and Cubic Units
The metric side is built to be tidy, and these identities remove most of the difficulty:
- 1 litre = 1,000 mL = 1,000 cm³ — a cube 10 cm on each side
- 1 m³ = 1,000 litres
- 1 mL = 1 cm³, which is why medical doses appear as cc
That last equivalence is the quickest route between a measured space and a liquid quantity: a tank 30 cm × 20 cm × 40 cm holds 24,000 cm³, which is 24 litres.
Volume Is Not Weight
Recipes that give flour in cups and butter in grams are mixing two incompatible systems, and no conversion factor joins them without knowing the density of the ingredient.
A US cup of water is 237 g. A cup of granulated sugar is about 200 g, and a cup of plain flour about 125 g — barely half the water figure for the same volume.
This is why baking by weight is more reliable than baking by volume: a cup of flour varies by 20% depending on whether it was scooped or spooned, and scales do not care.
Quick Reference
| Unit | US | Imperial |
|---|---|---|
| 1 gallon | 3.785 L | 4.546 L |
| 1 quart | 0.946 L | 1.137 L |
| 1 pint | 473 mL | 568 mL |
| 1 fluid ounce | 29.57 mL | 28.41 mL |
| 1 cup | 237 mL | 284 mL |
Frequently Asked Questions
- Is a US gallon the same as a UK gallon?
- No. A US gallon is 3.785 litres and an Imperial gallon is 4.546 litres, so the Imperial gallon is about 20% larger.
- How many millilitres are in a litre?
- Exactly 1,000. A litre is also 1,000 cubic centimetres, so 1 mL and 1 cm³ are the same volume.
- Why is a US fluid ounce larger than an Imperial one when the US pint is smaller?
- Because the pints divide differently. An Imperial pint holds 20 fluid ounces and a US pint holds 16, so the smaller pint is cut into fewer, slightly larger parts.
- Can I convert cups of flour to grams?
- Only if you know the ingredient. A cup measures volume, grams measure weight, and the bridge between them is density. A cup of flour is about 125 g, a cup of sugar about 200 g.