Unit converter

What it works out

This converts between metric and imperial units for building work: lengths in feet, inches and sixteenths, areas, volumes and gallons, weights and tons, paint spread rates, and application rates for adhesives and renders.

It's handy when a product's instructions, an old plan or an American video uses units you don't.

How it works

Choose what you're converting and the unit, and type a value. The calculator shows the usual counterpart in the other system first, then every other unit it knows, to six significant figures.

Every conversion uses the exact legal definitions, such as an inch being exactly 25.4 millimetres. Lengths in inches are also given to the nearest sixteenth, as they're marked on a tape measure. UK and US gallons and tons are different, and both are listed.

To convert feet and inches, choose ft + in and type each in its own box; inches are typed as decimals, so five and a half inches is 5.5. Nothing is rounded until it is shown, so the figures are safe to copy into an order or a spreadsheet.

A worked example

Converting a length of 3.81 m into feet and inches and the other units of length.

1. 3.81 m × 3.280839895 = 12 ft 6 in
2. An inch is exactly 25.4 mm, so a foot is 304.8 mm and a yard 914.4 mm.

Common mistakes

• Mixing up UK and US gallons. A US gallon is about a sixth smaller than a UK one. American paint coverage figures use US gallons.
• Mixing up tons and tonnes. A metric tonne, a UK ton and a US ton are three different weights.
• Rounding too early. Convert the final figure, not each step, or the rounding errors add up.
• Converting timber sizes. A nominal two-by-four isn't two inches by four once planed. Ask the merchant for the actual size.

Questions people ask