Unit conversions without the guessing
Use unit cancellation for length and power, and see why temperature conversions need an extra step.
Keep the unit attached
A bare number is easy to misread. Write both the starting quantity and the unit the answer requires. A length in inches and a length in millimetres describe the same dimension with different numbers.
Set up a factor that cancels
One inch is exactly 25.4 millimetres. Put inches on the bottom of the factor so the original inch unit cancels. The remaining unit is millimetres.
Check your direction
A millimetre is smaller than an inch, so the same length needs a larger number of millimetres. To reverse the conversion, divide by 25.4. For power, 1 kW is 1,000 W.
Treat temperature readings differently
Celsius and Fahrenheit have different zero points. For a temperature reading, subtract 32 before multiplying by 5/9. A temperature change uses only the scale factor, so do not subtract 32 from a temperature difference.
Carry the unit through.
Select a conversion and enter a value. The calculation below shows the operation, not just the answer.
Displayed to up to six significant digits.
Sense check: describe whether the output unit is bigger or smaller than the input unit.
Take this into your next practice session
Carry units through every line. Use the factor appropriate to the quantity, and keep unrounded values until the final answer. Nominal pipe sizes are labels, not dimensions to convert with this calculator.
References and authorship
Original examples and study notes by CodeSafe Canada. Updated September 12, 2026.