Volume is the unit category with the most variation across countries and contexts. Gallons vary between US and UK definitions. Cups vary between US, metric, and Australian versions. Fluid ounces are not metric ounces. Liters and milliliters, thankfully, are the same everywhere. Here's how to move between them all.

The critical distinction: US gallon vs imperial gallon

Two different units share the name "gallon":

  • US gallon = 3.785 liters (used in the United States)
  • Imperial (UK) gallon = 4.546 liters (used in the UK, some Caribbean countries)

A UK gallon is about 20% larger than a US gallon. This matters for fuel comparisons, recipe translations, and cross-border shopping. The US gallon dominates the online conversion world; always check if you're looking at a UK-sourced recipe.

Key conversion factors

  • 1 US gallon = 3.785 L = 128 fl oz US = 16 cups US
  • 1 US quart = 0.946 L = 32 fl oz US = 4 cups US
  • 1 US pint = 0.473 L = 16 fl oz US = 2 cups US
  • 1 US cup = 237 mL = 8 fl oz US
  • 1 US fl oz = 29.57 mL
  • 1 US tablespoon = 14.8 mL = 0.5 fl oz
  • 1 US teaspoon = 4.93 mL

Metric quick references

  • 1 liter (L) = 1,000 mL = 33.8 US fl oz = 1.057 US qt = 4.227 US cups
  • 500 mL = about 16.9 US fl oz (just over a US pint)
  • 250 mL = 8.45 fl oz (just over 1 US cup)
  • 100 mL = 3.38 fl oz

A 500 mL water bottle is a bit more than a US pint (473 mL). A 1 L bottle is just over a US quart (946 mL). A 2 L soda bottle is a bit over half a US gallon.

Fuel conversion: MPG vs L/100km

Fuel economy is reported differently in different countries:

  • US: Miles per gallon (MPG) — higher is better
  • Canada, most of Europe: L/100km — lower is better
  • UK: MPG using imperial gallons — higher is better

Conversion between US MPG and L/100km: L/100km = 235.215 / MPG.

  • 30 MPG = 7.84 L/100km
  • 25 MPG = 9.41 L/100km
  • 40 MPG = 5.88 L/100km

Also, a UK MPG figure is ~20% higher than the US MPG for the same car. A car rated "40 MPG UK" is really 33.3 MPG US.

Cooking volumes

US cooking dominantly uses cups, tablespoons, and teaspoons. International (and increasingly modern US) baking uses mL and g.

Common recipe-friendly approximations:

  • 1 cup ≈ 240 mL
  • 1/2 cup ≈ 120 mL
  • 1/4 cup ≈ 60 mL
  • 1 tbsp ≈ 15 mL
  • 1 tsp ≈ 5 mL

These are approximations — the exact US cup is 236.588 mL. Close enough for most recipes but not for precision pastry. Metric measuring cups outside the US often use 250 mL as "1 cup," which is Canadian/Australian standard.

Drinks and bottles

  • Wine bottle: 750 mL = 25.4 fl oz (about 5 glasses)
  • Beer (US standard): 12 fl oz = 355 mL
  • Beer (UK pint): 568 mL = 19.2 US fl oz
  • Coffee cup (US): typically 6 fl oz = 177 mL
  • Coffee mug: 10–12 fl oz = ~300–355 mL
  • Standard water bottle: 500 mL or 16.9 fl oz

Cocktails and bartending

Cocktail recipes use ounces (US fl oz) or milliliters:

  • 1 jigger = 1.5 fl oz = 44 mL
  • 1 pony = 1 fl oz = 30 mL
  • 1 dash ≈ 0.03 fl oz ≈ 1 mL

A well-balanced cocktail is usually 2 fl oz spirit + 1 fl oz sour + 0.75 fl oz sweet. In mL: 60 + 30 + 22.

Practical scenarios

European recipe calls for 250 mL of milk. Closest US-friendly measure: slightly over 1 cup. 250 mL = 1.057 cups.

Prescription says 10 mL three times daily. That's 2 teaspoons each dose, 30 mL total per day (about 1 fl oz).

Driving a rental car in Europe. The fuel gauge is in liters. A 50 L tank is about 13.2 US gallons.

Buying soda by the liter. A 2 L bottle is about 0.53 US gallons — slightly more than half a gallon.

Convert anything

Our volume converter handles gallons (US and imperial), quarts, pints, cups, fluid ounces, liters, milliliters, tablespoons, and teaspoons — every sensible combination. Enter one value and see all the others. Cooking, fuel, beverages, medicine — one tool, every unit. Volume has the most traps of any conversion category; the right calculator eliminates every one of them.