How it works
Each category defines a base unit. Converting multiplies by the source factor and divides by the target factor. Temperature converts to Kelvin with its own formula. Fuel economy converts to litres per 100 km first, then to the target scale.
- Temperature and fuel economy use their own formulas; everything else is a factor ratio.
Why it matters
Recipe measurements, travel distances, engineering specs and fuel bills all cross unit systems daily. A converter that handles the awkward categories — temperature and fuel economy — is the difference between a correct answer and a plausible-looking wrong one.
A worked example
One mile is exactly 1.609344 kilometres. Six litres per 100 km is 235.214583 ÷ 6.5 = 36.19 mpg US, or 282.4809363 ÷ 6.5 = 43.46 mpg UK.
Common mistakes
- Multiplying temperature values instead of using the offset formula.
- Chaining rounded results instead of converting from the original value.
- Treating L/100 km and mpg as proportional.
Practical tips
Convert from the original measurement each time rather than from a previous rounded result. For fuel comparisons, compare cars in the same unit — switching between mpg and L/100 km mid-comparison is where the numbers go wrong.
How to use it
- Open the tool. Everything runs in your browser tab.
- Paste or type your input, then choose the action you need.
- Check the result and copy it with one click.
Common questions
Why does temperature need its own formula?
Temperature scales have different zero points, so conversion is an offset plus a factor, not a simple ratio.
How exact are the conversion factors?
Standard defined factors are used, with display rounding to six decimals. Repeated conversions can accumulate display rounding.
Why does fuel economy run backwards?
Lower L/100 km is better, while higher mpg is better, so the scales are inversely related rather than proportional.
Is this tool really free?
Yes. There is no account, no paywall and no usage limit. Tools App is funded by aumenso, the studio behind it.
Is anything I enter uploaded?
No. The tool runs in your browser tab; what you enter is never sent to us and never stored.