Measurement › Unit converter

Unit converter

Type a number, pick two units — the answer appears. Then peek behind the curtain at the cancel-the-units trick that works for every conversion you'll ever do.

Unit converter

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The cancel-the-units trick

Every unit conversion is one move: multiply by a fraction that equals 1, chosen so the unit you don't want cancels and the unit you want is left standing. Watch:

Watch a conversion unfold

5 ft

Click 'Next step' to multiply by a clever 1.

Why this works

1 m = 100 cm is true, so the fraction (100 cm) / (1 m) equals 1. Multiplying anything by 1 doesn't change its value — only its units. The trick is choosing the version of 1 that cancels what you've got and leaves what you want.

The metric ladder

Hover the rungs — every step up or down moves the decimal point.

Metric ladder

Click any two rungs to see how the decimal point moves.

1 m = 100 cm

Decimal walk

Going from a big unit to a smaller one — the number gets bigger. Multiply by 10 2 times.

100.

1 m → 100 cm

The metric system always uses powers of 10 — so converting is just moving the decimal point.

Common conversions worth memorising

Quantity	Conversion	Memory hook
Length	1 inch = 2.54 cm	Two-and-a-half centimetres ≈ a thumb-tip width.
Length	1 km ≈ 0.621 miles	A mile is about 8 laps of a 200 m track.
Mass	1 kg ≈ 2.2 lb	A bag of sugar is about a kilo.
Volume	1 litre ≈ 1.06 US quarts	Big soda bottle.
Speed	60 mph ≈ 96.6 km/h	Highway speed in two systems.
Temperature	0 °C = 32 °F (water freezes)	The two scales kiss only at −40°.

Temperature is the odd one out

Most conversions are multiplications. Temperature has an offset: °C = (°F − 32) × 5/9. That's because both scales picked different zeros — Celsius at ice, Fahrenheit at a brine bath. There's no fraction that just "cancels degrees".

Common traps

kg vs lb — at the grocery store, 5 kg of potatoes is roughly 11 lb. Mixing up factor and offset has launched rockets the wrong way (the Mars Climate Orbiter, 1999, lost over a units mix-up).
fl oz vs oz — fluid ounce is a volume, ordinary ounce is mass. Same word, different things.
US gal vs UK gal — UK gallon is 1.2 US gallons. Two countries, same name, 20% difference.

Try it yourself

Convert your height to centimetres.
How many cm³ in a litre? (Hint: 1 mL = 1 cm³.)
A bullet train cruises at 320 km/h. In miles per hour?
Body temperature is 37 °C. What's that in Fahrenheit?

Answers: 1) Use the widget at the top. 2) 1000. 3) ≈ 199 mph. 4) 98.6 °F.