Volume Converter — Litres, Gallons & More

Volume measurements in the UK can be confusing, because UK gallons, pints and fluid ounces differ from their US namesakes. A UK pint is 568 ml while a US pint is only 473 ml, and a UK gallon of 4.546 litres is noticeably bigger than the US gallon of 3.785 L. This converter keeps imperial and US measures apart, so a recipe or a fuel figure does not quietly change size on the way across the Atlantic.

Supported units include litres, millilitres, UK and US gallons, UK and US pints, UK and US fluid ounces, cups on the US standard and tablespoons, which covers recipe conversion, fuel economy and liquid measurement generally. The base equivalents are that 1 litre is 1.760 UK pints or 0.220 UK gallons, a UK gallon is 8 pints, and a cup is 284 ml in the older UK sense against 237 ml in the US. Following one sum through, 2 UK gallons is 9.092 litres, 2.402 US gallons, 16 UK pints or 19.215 US pints.

Britain kept the pint where it mattered socially. Draught beer and cider in pubs must still be sold in pints by law, as must milk in returnable glass bottles, while fuel has been sold in litres since 1995. A pub pint glass has to hold 568 ml within ±2% and carry the HM Government crown stamp, which is why a short pour tends to get topped up rather than argued over.

Drink sizes follow from the pint and the metric bottle. A half is 284 ml. Wine comes by the glass at 125 ml, 175 ml or 250 ml, poured from a 750 ml bottle that gives 6 medium glasses, and champagne fills 6 flutes from the same 750 ml. Spirits bottles hold 700 ml, and a single measure is 25 or 35 ml in England and Wales, with the pub obliged to display which it serves, while Scotland defaults to 25 ml. Soft drinks come in 330 ml cans, 500 ml bottles and 2L bottles, and milk in 1L cartons or the imperial 2-pint at 1,136 ml and 4-pint at 2,272 ml.

In the kitchen, volume is mostly a question of portioning. Soup is scaled at 250 ml a head as a starter and 400 ml as a main. Filter coffee uses 30g of grounds per 500 ml of water, while an espresso takes 18-20g for a 36 ml shot. A braise such as boeuf bourguignon typically calls for half a bottle of wine, 375 ml, and a stock cube makes up 500 ml. A 400g tin of tomatoes stands in for about 6 medium fresh ones, and Yorkshire puddings want 1 tsp of oil in each hole. Read a measuring jug at eye level, allowing for the meniscus, the slight curve the liquid takes against the side of the jug.

At industrial scale the same units grow quickly. A road petrol tanker carries around 38,000 L. A domestic heating oil tank holds 1,200-1,800 L, and most suppliers set a minimum delivery of 500 L. Skips are still sold in cubic yards, with a mini at 2 yd³ or 1.5 m³, a midi at 4 yd³, a builder's skip at 6-8 yd³ and a roll-on roll-off at 20-40 yd³. A 20ft shipping container gives 33 m³ and a 40ft container 67 m³. Water bills are metered in cubic metres, where 1,000 L makes 1 m³, and an average UK household uses 100-150 m³ a year, against 2,500 m³ for an Olympic swimming pool.

Physics ties volume to mass through density, written as ρ = mass ÷ volume. Water is the reference at 1 g/ml at 4°C, iron comes in at 7.87 g/cm³, gold at 19.3 g/cm³ and balsa wood at 0.13 g/cm³. Gases behave differently, since their volume responds to pressure and temperature. Boyle's Law holds that P×V stays constant at a fixed temperature, Charles's Law that V/T stays constant at a fixed pressure, and the ideal gas law combines both as PV = nRT. That is why a car tyre reads higher when hot, and why heating the air in a balloon leaves it lighter than the air around it and produces lift.