Work out font size for distance instantly with clear inputs, formula shown and shareable results.
Character height is set by the angle it subtends at the eye: height equals twice the distance times the tangent of half the target angle in arc minutes. Around 20 arc minutes is comfortable for sustained reading, which is why 16 px body text at arm's length and a 40 mm slide heading at the back of a room are equivalent.
Physical height
height = 2 x distance x tan(arc minutes / 60 / 2 in degrees)
Point size
points = height in mm x 2.8346
height = 2 x distance x tan(arc minutes / 60 / 2 in degrees). Character height is set by the angle it subtends at the eye: height equals twice the distance times the tangent of half the target angle in arc minutes.
Around 20 arc minutes is comfortable for sustained reading, which is why 16 px body text at arm's length and a 40 mm slide heading at the back of a room are equivalent.
Enter reading distance, target character height in arc minutes, screen pixel density. The defaults shown are a realistic worked example — swap in your own figures to get a result you can use.