Work out signage letter height instantly with clear inputs, formula shown and shareable results.
Signage legibility follows a fixed ratio of viewing distance to cap height, commonly one millimetre of letter height for every 250 millimetres of distance. The ratio derives from the eye's angular resolution, which is why the same rule works for a shop fascia and a motorway gantry at very different scales.
Letter height
cap height mm = viewing distance mm / legibility ratio
cap height mm = viewing distance mm / legibility ratio. Signage legibility follows a fixed ratio of viewing distance to cap height, commonly one millimetre of letter height for every 250 millimetres of distance.
The ratio derives from the eye's angular resolution, which is why the same rule works for a shop fascia and a motorway gantry at very different scales.
Enter maximum viewing distance, legibility standard. The defaults shown are a realistic worked example — swap in your own figures to get a result you can use.