Science and units
Power and energy cost
Watts and hours to units (kWh) and cost, at the per-unit rate on your own electricity bill.
Class 6 to 12, families, makers
Science and units
Unit converter for science and maths
Convert between metric, imperial and everyday units with the exact factors. See the working and the value in every unit at once, handy for physics numericals and project measurements.
- Made forClass 6 to 12, diploma, makers
- Shows the workingEvery step, ready for your practical file
- Instant answersResults change as you type
Convert units
Choose what you are measuring, type the value and pick the units. The table shows the value in every unit at once.
Length1 in = 2.54 cminch to centimetre
- 1 in in cm
- 2.54
- 1 cm in in
- 0.3937007874
Working
- 1 inch = 0.0254 m; 1 centimetre = 0.01 m.
- 1 in × 0.0254 ÷ 0.01 = 2.54 cm.
- So 1 in = 2.54 cm and 1 cm = 0.3937007874 in.
- Note: The factors are the exact defined values (shown to 12 significant figures); results are rounded to 10.
1 in in every unit
| Unit | Value |
|---|---|
| micrometre | 25,400 µm |
| millimetre | 25.4 mm |
| centimetre | 2.54 cm |
| metre | 0.0254 m |
| kilometre | 0.0000254 km |
| inch | 1 in |
| foot | 0.08333333333 ft |
| yard | 0.02777777778 yd |
| mile | 0.000015782828 mi |
| nautical mile | 0.000013714903 nmi |
What it works out
Understanding unit conversion
Every measurement is a number and a unit. A physics answer without its unit loses marks, and many numericals go wrong because units are mixed: centimetres with metres, km/h with m/s, grams with kilograms.
The converter uses the exact defined factors (an inch is exactly 2.54 cm, a pound is exactly 0.45359237 kg, a standard atmosphere is exactly 101,325 Pa) and shows the working, so you can do the same conversion on paper.
Formula and worked example
Working out unit conversion by hand
The calculator uses exactly these formulas. Write them in your notebook and check one answer by hand: it is the surest way to remember them.
The formula
- New value = old value × (size of old unit ÷ size of new unit)
- °F = °C × 9/5 + 32; K = °C + 273.15
- km/h to m/s: × 5/18 (divide by 3.6)
- size of a unit
- its value in the base unit, for example 1 inch = 0.0254 m
- °C, °F, K
- temperature scales with different zeros, so they need a formula
Worked example
72 km/h in metres per second
- 1 km = 1,000 m and 1 h = 3,600 s.
- 72 km/h = 72 × 1,000 ÷ 3,600 m/s.
- = 72 × 5/18 = 20 m/s.
- Check: 20 m/s × 3.6 = 72 km/h.
Answer20 m/s
In projects and exams
How students use it
Length, mass, time, temperature, speed, area, volume, energy and pressure, with exact factors. Here is where it earns its place in a school year.
Physics numericals
Convert every quantity to SI units before you substitute into a formula.
Project measurements
Turn inch sizes from a plan or a component datasheet into centimetres for your model.
Temperature experiments
Move between Celsius, Fahrenheit and kelvin with the working shown.
Maps and land
Convert square feet, acres and hectares for geography and maths projects.
Check your work
Common mistakes to avoid
These are the slips that cost marks in exams and burn out parts on the bench.
Converting area like length
1 m = 100 cm, but 1 m² = 100 × 100 = 10,000 cm². Volume is cubed: 1 m³ = 10,00,000 cm³.
Treating temperature as a factor
20 °C is not "twice as hot" as 10 °C, and °C to °F needs the + 32.
Mixing up US and UK gallons
A US gallon is 3.785 L and a UK gallon is 4.546 L.
Calories on food labels
A food "Calorie" is a kilocalorie: 1,000 calories.
Questions
Questions about unit conversion
Stuck on a project or a sum? Ask the institute on WhatsApp.
Ask on WhatsAppWhy is 1 m² equal to 10,000 cm²?
A square metre is 100 cm long and 100 cm wide, so it holds 100 × 100 = 10,000 square centimetres.
How do I convert km/h to m/s quickly?
Multiply by 5 and divide by 18 (or divide by 3.6). To go back, multiply by 18/5 (or 3.6).
What is a quintal?
A quintal is 100 kg, a unit still used for farm produce in India. A tonne is 1,000 kg, or 10 quintals.
Why are bigha and other local land units missing?
Their size differs from state to state and even district to district, so no single factor is correct. Use the figure your local land records office gives.
Free ebooks
Read more about unit conversion
Free PDF ebooks in easy English: download, print and share them.
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