Volume Converter

Converting volume and capacity: the factors, and which ones are exact

This converter handles 16 volume and capacity units, all of them passing through L. Below are the factors it uses, so you can check any result by hand — and a note on which of them are exact by definition and which are conventions that depend on conditions.

How it works

• Converts between every pair of volume and capacity units at once, rather than one pair at a time.
• Uses the defined values, not rounded approximations — an inch is exactly 0.0254 m, not 0.0254001.
• Routes everything through L, so adding a unit cannot break the existing pairs.
• Marks units whose factor depends on conditions, instead of presenting a convention as a constant.

every unit converts through L

  Millilitres (ml)         0.001
  Litres (L)               1
  Cubic centimetres (cm³)  0.001
  Cubic metres (m³)        1000
  Cubic inches (in³)       0.016387064
  Cubic feet (ft³)         28.316846592
  Teaspoons (US)           0.00492892159375
  Tablespoons (US)         0.0147867647812
  Fluid ounces (US)        0.0295735295625
  Cups (US)                0.2365882365
  Pints (US)               0.473176473
  Quarts (US)              0.946352946
  Gallons (US)             3.785411784
  Fluid ounces (imperial)  0.0284130625
  Pints (imperial)         0.56826125
  Gallons (imperial)       4.54609

to convert: value x factor(from) / factor(to)

Worked example

A worked volume and capacity conversion, step by step.

1. start 1 Gallons (US)
2. to the base unit 1 x 3.785411784 = 3.785411784 L
3. into the target 3.785411784 / 1
4. result 3.785411784 Litres (L)

Multiplying into the base unit and dividing out again is the whole method. It is worth doing once by hand, because it shows that a converter is only ever as good as its factors — and that a wrong factor produces a plausible-looking number rather than an obvious error.

Reading the result

• US and imperial units share names and are not the same size. An imperial pint is 568 ml against a US pint's 473, and an imperial gallon holds 160 fluid ounces where a US gallon holds 128 — so an imperial fluid ounce is also slightly smaller. A recipe that says "a pint of milk" means noticeably different amounts on either side of the Atlantic, which is why the two families are listed separately here rather than merged.
• Most of these factors are exact by international agreement rather than measured. The inch, the pound, the nautical mile and the standard atmosphere all have defined values, which is why the tool can show a conversion landing on a round number and be right rather than lucky.
• Results are rounded for display, not in the arithmetic. Conversions run at full double precision and only the printed value is shortened, so chaining conversions here does not accumulate rounding error the way copying rounded figures between steps would.

Common questions

Why does my result differ slightly from another converter?

Almost always because the other one rounded a factor. A converter that stores a US gallon as 3.7854 litres rather than 3.785411784 will drift in the fourth significant figure, and the drift compounds if you convert twice. Check a defined value you know — a US gallon should come out as exactly 231 cubic inches — and the rounded converter will show it as 230.99 or 231.01.

Does converting through a base unit lose accuracy?

Not meaningfully. Two floating-point operations instead of one adds error in the sixteenth significant figure, far below anything you would measure. What it buys is consistency: every pair uses the same two factors, so the table cannot contain a pair that disagrees with the rest of it.