Volume units explained
This is the category where the same word means two different sizes. A gallon, a pint and a fluid ounce are all larger in Britain than in America, so every one of them appears here twice, labelled, rather than once and averaged.
Millilitre mL
1 mL = 0.001 L Exact
A thousandth of a litre, and identical to a cubic centimetre — which is why engine sizes appear as both 1600 cc and 1.6 litres. Medicine doses, small bottles and most non-US recipes work in millilitres.
Litre L
1 L = 1 L Exact
A cubic decimetre: a cube ten centimetres on each side. Water was the design brief — one litre of it weighs almost exactly one kilogram, which is why metric cooking can swap between weight and volume for water and nothing else.
Cubic metre m³
1 m³ = 1,000 L Exact
A thousand litres. The unit of water bills, concrete orders, shipping volume and room air changes. A cubic metre of water weighs a tonne, which is a useful pairing to keep in mind when someone quotes you a tank size.
US teaspoon tsp
1 tsp = 0.004928921594 L Exact
Just under 5 mL. Nominally the same everywhere, but the metric teaspoon used in Australia and much of Europe is exactly 5 mL, so a recipe crossing borders drifts slightly. Rarely enough to matter outside baking.
US tablespoon tbsp
1 tbsp = 0.01478676 L Exact
Three US teaspoons, about 14.8 mL. This one does vary: the Australian tablespoon is 20 mL, four teaspoons rather than three, which is a 35% difference and enough to ruin a sauce.
US fluid ounce US fl oz
1 US fl oz = 0.02957353 L Exact
About 29.6 mL. Note that it is larger than the Imperial fluid ounce despite the US gallon being smaller — the two systems divide differently, so nothing about them scales together. Also not a mass: an ounce of gold and a fluid ounce of water are unrelated.
US cup US cup
1 US cup = 0.23658824 L Exact
About 237 mL for the customary cup used in recipes, or 240 mL for the US legal cup on nutrition labels. Neither is the 250 mL metric cup used in Australia. This is why experienced bakers weigh flour instead — a cup of it can vary by 20% depending on how it was scooped.
US pint US pt
1 US pt = 0.47317647 L Exact
Sixteen US fluid ounces, about 473 mL. Noticeably smaller than the British pint, which catches visitors out in both directions — a pint of beer in London is nearly a fifth larger than one in Boston.
US quart US qt
1 US qt = 0.94635295 L Exact
A quarter of a US gallon, two US pints, about 946 mL. Close enough to a litre that American recipes and metric ones can often be swapped without disaster, though the 5% gap adds up in a large batch.
US gallon US gal
1 US gal = 3.785412 L Exact
Exactly 3.785411784 litres, and historically the English wine gallon rather than the corn or ale gallons that competed with it. Because it is about 17% smaller than the Imperial gallon, American fuel economy figures look worse than British ones for the same car.
Imperial fluid ounce imp fl oz
1 imp fl oz = 0.02841306 L Exact
About 28.4 mL — smaller than the US fluid ounce, even though the Imperial gallon is bigger. The Imperial gallon divides into 160 of these; the US gallon into 128 of its own. The two systems simply do not line up anywhere.
Imperial pint imp pt
1 imp pt = 0.56826125 L Exact
Twenty Imperial fluid ounces, about 568 mL. Legally protected in the UK for draught beer, cider and doorstep milk, which is why it survived metrication when almost nothing else did.
Imperial gallon imp gal
1 imp gal = 4.54609 L Exact
Exactly 4.54609 litres, defined in 1824 as the volume of ten pounds of water. Still used for fuel economy figures in the UK and Ireland even though fuel itself has been sold in litres for decades — which is why a British mpg number is always flatteringly higher than an American one.
Cubic foot ft³
1 ft³ = 28.316847 L Exact
1,728 cubic inches, about 28.3 litres. Common for appliance capacity, freight volume and natural gas in the United States. The cube of the foot, so the number grows fast: doubling a box's dimensions multiplies its volume by eight.
Cubic inch in³
1 in³ = 0.01638706 L Exact
About 16.4 mL. American engine displacement was quoted this way for decades — a 350 cubic inch V8 is 5.7 litres — and it is still how you will see classic car engines described.
Oil barrel bbl
1 bbl = 158.987295 L Exact
The oil barrel: 42 US gallons, about 159 litres. The 42 is inherited from 1860s Pennsylvania, where a 40-gallon barrel plus two gallons for leakage in transit became the standard. It is now purely a unit of account; oil has not moved in actual barrels for a very long time.