How to Choose the Right Unit for a Measurement
A practical guide to choosing units that make measurements easy to understand, compare and communicate.
In this guide
Start with the person reading the number
The best unit is not always the smallest or most precise one. Choose a unit that your reader is likely to understand immediately. A distance across a town may make sense in kilometres, while a small object may be easier to describe in centimetres.
Keep the same unit when comparing values
If you are comparing measurements, put them into the same unit first. Comparing 2 metres with 180 centimetres without converting one of them makes the numbers look different even though the quantities are close.
Do not hide useful precision
A conversion can produce many decimal places, but that does not mean every decimal is meaningful. Match the number of decimal places to the accuracy of the original measurement and the purpose of the result.
Use the converter as a check
When a unit matters for a technical, financial or safety-related decision, use the calculator to check your arithmetic and then confirm the required unit and specification from the relevant source.
Try the related tool
If you came here because you need to do the calculation or create something now, you can use the matching KingToolsKit tool and then come back to the guide when you want the explanation.
Open the tool →