Sign Visibility Calculator

Calculate minimum and recommended letter heights for sign legibility at a given viewing distance and vehicle speed.

Viewing Distance (ft)

Vehicle Speed (mph)

Reaction Time (sec)

Tab to move between fields

Min Letter Height

16.7 in

≈ 5 credit cards

Recommended Height

20 in

≈ 6 credit cards

Est. Sign Width10 ft

Reaction Dist (ft)198

How to Use This Calculator

Enter the viewing distance (ft) and vehicle speed (mph).
Review minimum and recommended letter height (in) for legibility at the given distance and speed.
Check recommended sign width (ft) for the letter layout.
Use the 1-inch-per-30-feet rule as a starting point: a sign read at 300 ft needs 10-inch letters minimum.
High-contrast color combinations (dark on light, yellow on black) allow slightly smaller letter sizes.

How the result changes with Viewing Distance (ft)

Viewing Distance (ft): Maximum distance from which the sign should be readable
Vehicle Speed (mph): Speed of passing traffic (affects how much reading time the driver has)
Reaction Time (sec): Time a driver needs to read, comprehend, and react to the sign (3 sec is standard)

Identify Input Parameters
Viewing Distance (ft) = 500, Vehicle Speed (mph) = 45, Reaction Time (sec) = 3 = 3 input(s) provided
Calculate Min Letter Height
Min Letter Height
16.7 = 16.7
Calculate Recommended Height
Recommended Height
20 = 20