Metric and imperial conversion drill
Convert inches to millimetres and feet to metres, both ways. Type the answer; it is marked with a small tolerance so a reasonable rounding counts, and the working is shown when you miss.
This drill needs JavaScript to generate and mark questions. Turn it on to practice — the explanation below works either way.
The two constants
One inch is exactly 25.4 mm; one foot is exactly 0.3048 m. Everything here runs off those two. Inches to millimetres: multiply by 25.4 — so 3.5" is 3.5 × 25.4 = 88.9 mm. Feet to metres: multiply by 0.3048 — so 10 ft is 10 × 0.3048 = 3.048 m. Reverse each by dividing instead. Because both figures are exact definitions, the conversions are exact too; the only rounding is whatever you choose at the end.
Questions people ask
How many millimetres are in an inch?
Exactly 25.4. It is a defined value, not a rounded one, so an inch is 25.4 mm on the nose. To go from inches to millimetres multiply by 25.4; to go back, divide by 25.4.
And feet to metres?
A foot is exactly 0.3048 metres. Multiply feet by 0.3048 for metres, divide metres by 0.3048 for feet. Both conversions are exact definitions, which is why they never drift.
Why practise conversions?
Because prints, fittings and materials mix the two systems, and doing the swap in your head keeps you moving instead of reaching for a phone. A little drilling makes 25.4 and 0.3048 as automatic as your times tables.
Related
- Fraction and decimal drill — the inch side of it.
- Formula sheets — a fraction, decimal and millimetre chart to print.
- All drills
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