Volume Converters 24
Volume is where unit names get dangerous. A gallon means 3.785 L in the US, 4.546 L in the UK, and 4.405 L if you're measuring grain. A tablespoon is 14.8 mL in the US, 15 mL in the UK, and 20 mL in Australia — a 35% spread. A cup is 236.6 mL in US recipes, 250 mL in metric countries, and 284.1 mL if it's an imperial cup. Every conversion on this page specifies which definition it uses. When in doubt: use milliliters — they're the same everywhere.
Read the Volume & Cooking Conversion Guide
Three different gallons, four different cups, and a 20% fuel error waiting at 35,000 feet. From French baking recipes to concrete pours to Olympic swimming pools — every volume catastrophe starts with assuming a word means the same thing everywhere.
Open the full guide →Volume: Three Gallons, Four Cups, Endless Confusion
Volume conversion is uniquely treacherous because the same word — gallon, cup, pint — means different quantities in different countries. The US liquid gallon (3.785411784 L) is defined as 231 cubic inches. The imperial gallon (4.54609 L) is defined as the volume of 10 pounds of water at 62°F — about 20% larger. The US also has a separate dry gallon (4.40488377086 L), used historically for grain. Using the wrong gallon in aviation fuel calculations has caused at least one known incident — Air Canada Flight 143 (the "Gimli Glider") ran out of fuel mid-flight because the ground crew calculated fuel weight using pounds/liter instead of kilograms/liter.
Cooking volumes add another layer: a US cup is 236.5882365 mL (8 US fluid ounces), while a UK cup is 284.131 mL (10 imperial fluid ounces), and a metric cup (used in Australia and New Zealand) is 250 mL. A tablespoon is 15 mL in most countries but 20 mL in Australia. These differences are why professional kitchens weigh ingredients rather than measure by volume.
Volume Conversion Constants
1 US gallon = 3.785411784 L (NIST Handbook 44)
1 imperial gallon = 4.54609 L (UK Weights and Measures Act 1985)
1 US cup = 236.5882365 mL | 1 US fl oz = 29.5735295625 mL
1 cubic foot = 28.316846592 L (exact, from 1 ft = 0.3048 m)
For the engineering stories — the Gimli Glider, cooking-scale disasters, and why metric recipes use weight — see the Volume & Cooking Conversion Guide.
The Gimli Glider: How a Gallon-Liter Confusion Glided a 767
On July 23, 1983, Air Canada Flight 143 — a Boeing 767 — ran out of fuel at 41,000 feet over central Canada. The aircraft, carrying 61 passengers and 8 crew, glided 17 minutes without engines to a dead-stick landing at a decommissioned RCAF base in Gimli, Manitoba. No one died. The cause was a unit conversion error.
Canada was halfway through metrication. The 767 was Air Canada's first metric aircraft — its fuel gauges read in kilograms. The ground crew, still working in the imperial system, calculated the fuel load in pounds. The conversion from litres to kilograms requires knowing the fuel's density (Jet A-1: ~0.803 kg/L at 15°C). The ground crew used pounds/litre instead of kilograms/litre. The aircraft took off with roughly half the fuel the crew believed they had. The fuel gauges were unserviceable — the crew relied entirely on the ground crew's dipstick measurement and their own manual calculation. Both gauges and math failed on the same flight.
The Gimli Glider is taught in every aviation human-factors course, every engineering ethics class, and every metrology textbook. The failure was not arithmetic — the arithmetic was correct given the wrong unit. The failure was a system that allowed two different unit systems to coexist at a safety-critical handoff without a verification step that either system alone would have caught. The 767's fuel totalizer read in kilograms. The refueling truck measured in litres. The conversion required density. The density was entered with the wrong unit. Three different quantity systems met at one valve, and none of them spoke the same language. For the full technical breakdown, see the Volume & Cooking Conversion Guide.
Why Professional Kitchens Weigh, Not Measure
US cup = 236.6 mL | UK cup = 284.1 mL | Metric cup = 250 mL
US tbsp = 14.79 mL | UK tbsp = 15 mL | AU tbsp = 20 mL
1 US fl oz = 29.57 mL | 1 UK fl oz = 28.41 mL
A French pastry recipe calling for "250 g of flour, 200 g of sugar, 100 g of butter" works identically in Paris, London, New York, and Tokyo — the gram is the gram. The same recipe calling for "2 cups of flour, 1 cup of sugar, 1/2 cup of butter" produces different results in each city because the cup itself is different. This is why professional baking has fully metricated globally: the ingredient list is in grams, the oven is in Celsius, and the only volume measurement is the litre for liquids, which is identical everywhere. The home cook bridging an American recipe to a metric kitchen must convert cups to milliliters and fluid ounces to milliliters — and must know which cup and which fluid ounce the recipe uses.