Unit Conversion Quiz
Convert each measurement and pick the right answer. Approximate conversions are rounded, so look for the closest value. 10 questions per round.
How the quiz works
The first level stays inside the metric system, where every conversion is a power of ten and the answers are exact. The second crosses into the imperial units still used every day — inches, pounds, miles and feet — and the third adds temperature and a few units of volume and length. Imperial conversions rarely come out even, so those answers are rounded and the question shows ≈ rather than =.
After every answer, right or wrong, the quiz shows the conversion factor used — 1 in = 2.54 cm, or °C = (°F − 32) × 5/9 — because the factor is the part worth remembering. The wrong options come from real mistakes: the decimal point moved the wrong way, a factor applied backwards, or the 32 forgotten in a temperature.
Where the numbers come from
Several imperial units are now defined exactly in metric terms. Since an international agreement in 1959, the inch has been exactly 2.54 centimetres and the pound exactly 0.45359237 kilograms, which makes the mile exactly 1.609344 kilometres. The imperial system is, in practice, a set of fixed multiples of metric units.
Getting a conversion wrong is not only a school problem. NASA lost the Mars Climate Orbiter in 1999 because one team's software reported thrust in pound-force seconds while another expected newton-seconds, and the spacecraft approached Mars far lower than planned.
Shortcuts for doing it in your head
- Metric prefixes do all the work: kilo is a thousand, centi a hundredth, milli a thousandth. Converting is just moving the decimal point that many places.
- Kilometres to miles: multiply by 0.6. A 10 km run is about 6 miles; a marathon's 42.2 km is 26.2 miles.
- Kilograms to pounds: double it and add ten percent. 70 kg becomes 140 + 14 = 154 lb.
- Fahrenheit to Celsius, roughly: subtract 30 and halve. 80°F gives about 25°C; the exact answer is 26.7°C.
- Inches to centimetres: multiply by 2.5 and add a little. A 55-inch screen is a bit under 140 cm across the diagonal.
Frequently asked questions
Which conversions are included?
Metric covers kilometres, metres, centimetres, millimetres, kilograms, grams, litres and millilitres. Everyday imperial adds inches, pounds, miles and feet. Temperature & more has Fahrenheit and Celsius, ounces, US gallons and yards.
Why are some answers rounded?
Conversions between metric and imperial rarely come out even — 55 inches is 139.7 cm, 10 miles is 16.09 km. Those answers are rounded to one decimal place, or to a whole number above 100, and the question shows ≈ instead of =. The wrong options are always far enough away that rounding never makes the choice unclear.
How are the wrong options chosen?
From the usual mistakes: moving the decimal point the wrong way or by the wrong number of places, applying a factor backwards (dividing by 2.54 instead of multiplying), and in temperature, forgetting the 32 or using 5/9 where 9/5 belongs.
Which gallon do you use?
The US gallon, 3.785 litres. The imperial gallon still used in the UK is larger, about 4.546 litres, which is a common source of confusion when comparing fuel economy figures.
Which numbers format do you use?
Numbers are written without thousands separators and with a decimal point, so 2500 m and 2.5 km can never be misread.
Is this useful in real life?
Very. Screen sizes are sold in inches almost everywhere, running races are measured in both miles and kilometres, weather apps switch between Fahrenheit and Celsius, and recipes cross between cups, ounces and grams.