Unit converter
mm/inch, metres/feet, kg/lb, litres/gallons — pick a pair, pick a direction, get the answer instantly.
Choose a conversion
Drag to any value, or use the arrow keys for fine control.
Converted value
— 100 mm converts to 3.937 in.
Standard conversion factors. Gallons are imperial (4.54609 litres), the one used in the UK — not the US gallon.
Most jobs run on a mix of units — a spec sheet in mm, a customer who thinks in feet and inches, a delivery note in kg when the quote was done in stone. This tool covers the four conversions that come up most often on a UK trades job: millimetres and inches, metres and feet, kilograms and pounds, and litres and gallons — pick the pair, pick the direction, and drag the slider to any value.
Why these four
Timber and fittings still come in inches often enough that translating a spec into mm matters, older drawings and some trade customers still think in feet rather than metres, appliance and material weights get quoted in both kg and lb depending on where they're sourced, and fuel, water and chemical volumes swing between litres and gallons depending on the supplier. None of these conversions are hard — they're just the kind of thing you don't want to be doing long division for standing in a builders' merchant.
A worked example
A door spec calls for a 35mm thick leaf, but the timber merchant only lists stock in inches. Switch to mm ↔ inch, set 35mm, and the answer comes back as 1.378in — close enough to know you're looking for 1⅜in stock, the standard size. Same principle for a fitting quoted in pounds when your supplier invoices in kilograms, or a tank capacity given in gallons when the spec sheet wants litres.
What this isn't
The litres/gallons conversion uses the imperial gallon (4.54609 litres) — the one used in the UK — not the US gallon, which is smaller. If you're working from a US spec sheet or US-sourced materials, double-check which gallon it means before ordering. This tool rounds for display but keeps full precision internally, so chaining a conversion back and forth returns you to the original figure rather than drifting with each rounding step.
It's a straight unit conversion, not a materials calculator — it won't tell you how many boards you need or what a job costs, just the number itself. For quantity or coverage sums, the other free tools on this site handle the materials-specific maths; this one is purely for translating a figure from one unit into another when you've already got the number in hand.
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