Legibility at a distance: how big should letters be on a banner, wall or stand
Enter the distance from which people will read the text and get the letter height and type size for three levels: minimum, comfortable reading and quick glance. It also works in reverse: enter a letter height and check the reading range. Accounts for contrast, lighting, a moving viewer and age. The results are indicative design recommendations.
Viewing conditions
Type size (pt) is not letter height: capitals usually take 0.66–0.73 of the size. The conversion to points is approximate and depends on the typeface.
Result
The result is an indicative design recommendation, not a standard. Safety, accessibility and road signage have separate requirements, and the needs of visually impaired viewers go beyond this calculator.
Visual angle
How big do letters have to be to be readable from a distance?
Legibility depends on the angle at which the eye sees a letter, not on its size alone. A 10 cm letter seen from 10 m fills the same part of the visual field as a 1 cm letter from 1 m. That is why the required height is derived from the distance: h = 2 · d · tan(θ/2), where θ is the visual angle. A person with normal vision recognises letters at a few arcminutes, but comfortable reading needs about 15 arcminutes, and text read in motion, from afar or in poor conditions needs 30 or more.
Three levels: minimum, comfortable reading, quick glance
Minimum (8′) is an indicative recognition threshold for a short sign in very good conditions with an attentive viewer; do not design longer text at this level. Comfortable reading (15′) suits most uses: posters, stand walls, shop windows, presentations. Quick glance (30′) gives a large margin when the viewer has a fraction of a second or looks from afar: roadside banners, vehicle advertising, directional signage. Example: from 10 m, comfortable reading needs a cap height of about 44 mm, a quick glance about 87 mm. Low contrast, poor lighting, motion and older viewers raise the requirements, so the tool multiplies the result by indicative factors and shows the resulting angle after that correction.
Type size vs. letter height, stroke weight and regulations
Type size in points describes the character body, not the letter height: the capitals of most typefaces are 0.66–0.73 of the size, so a "100 pt" sign has capitals about 25 mm tall. The tool converts cap height to points for the chosen proportion. At a distance, stroke weight matters too: thin-stroke typefaces "disappear", so for long distances a stroke of about 1/7 of the cap height is an indicative starting point; when reversed out (light letters on a dark background) avoid thin typefaces, and the exact weight depends on the printing technique and illumination. The results are indicative design recommendations: safety, accessibility and road signage are governed by separate standards that must be checked independently, and the needs of visually impaired viewers go beyond this calculator.
