Unit Conversion Factor Calculator
Convert a value with any conversion factor you supply — enter how many target units make one source unit and get the result plus the inverse factor.
How it works
Target = source value × factor · Inverse factor = 1 ÷ factor
A conversion factor is a ratio equal to 1 — like 1.60934 km per 1 mi — so multiplying by it changes the units without changing the real quantity. Set it up so the unit you are leaving sits on the bottom and cancels, leaving the unit you want. The inverse factor simply flips the ratio, which is what you multiply by to go back the other way.
Worked example
Convert 5 miles to kilometres with the factor 1.60934 km per mile: 5 × 1.60934 = 8.0467 km. The inverse factor, 1 ÷ 1.60934 = 0.6214, converts kilometres back to miles.
Frequently asked questions
What exactly is a conversion factor?
It is a fraction whose top and bottom are the same physical amount in different units, so it equals 1. Multiplying by it is legal because you are multiplying by one — only the label on the number changes.
Which way round should the factor go?
Put the unit you want on top and the unit you have on the bottom, so the old unit cancels. If you have miles and want kilometres, use km on top: 1.60934 km / 1 mi.
How do I convert back?
Use the inverse factor, which this calculator shows. It is just 1 divided by your factor, and multiplying by it reverses the conversion exactly.
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This calculator is for educational purposes. Double-check important results before acting on them.