conversion factor; scale factor
Technical term used in mathematics, science, and engineering to convert between units or scales.
Using this conversion factor, you can convert miles to kilometers.
To calculate the map scale, a scale factor is needed.
Similar meaning; 変換係数 is also used for conversion factors, but 換算係数 often implies a fixed ratio for unit conversion.
Compound of 換算 (conversion) and 係数 (coefficient).