Sign Character Height and Viewing Distance (2010 ADA Standards 703.5.5)
Sign letter height, from how high it sits and how close a person can get.
Example
You enter
- Height of the character BASELINE above the finish floor (in) 60
- Horizontal viewing distance to the obstruction preventing approach (in) 120
- Character height provided, uppercase I (in) 0.625
You get
- Required character height (in) 1.125
- Base height (in) 0.625
- Added (in) 0.5
- Provided vs required SHORT by 0.500 in
- How far these characters serve 72.0 in (6.0 ft) in this band
Checked against published worked examples from: US Department of Justice / US Access Board.
Details, formula, and sources
ScopeLetter height is not a design choice: Table 703.5.5 reads it off how high the characters sit and how close a person can actually get, adding 1/8 in for every foot of viewing distance past the band threshold. The band boundaries are cliffs, not ramps -- a baseline at 70 in needs 5/8 in characters and the same sign raised a tenth of an inch needs 2 in, because the base jumps bands. Two measurement rules do most of the damage: the height is to the BASELINE, not the panel, and the viewing distance runs to whatever OBSTRUCTION prevents further approach, so pulling out the counter in front of a sign makes the distance SHORTER, not longer.
Formula or tablerequired visual character height = base + (max(0, viewing distance - band threshold) / 12) x 1/8 in, where the band is set by the height of the character baseline above the finish floor: 40 to 70 in -> base 5/8 in, threshold 72 in; over 70 to 120 in -> base 2 in, threshold 180 in; over 120 in -> base 3 in, threshold 252 in (21 ft).
Source and edition2010 ADA Standards for Accessible Design, 703.5.5 and Table 703.5.5 (Visual Character Height). A US federal standard in the public domain, quoted directly.
Free accessThe 2010 ADA Standards are published in full at no cost at ada.gov and by the US Access Board.
What governsEstimate. AHJ and licensed professional govern.
API field namesbaseline_height_in, viewing_distance_in, provided_character_height_in, required_character_height_in, base_height_in, added_in, shortfall_in, max_viewing_distance_in
- Band 1 baseline 40 to 70 in above the floor: 5/8 in, plus 1/8 in per foot of viewing distance above 72 inTable 703.5.5
- Band 2 baseline over 70 to 120 in: 2 in, plus 1/8 in per foot of viewing distance above 180 inTable 703.5.5
- Band 3 baseline over 120 in: 3 in, plus 1/8 in per foot of viewing distance above 21 ftTable 703.5.5
- Height measurement to the baseline of the characters, not the panelTable 703.5.5
- Viewing distance the horizontal distance to an obstruction preventing further approach towards the sign2010 ADA Standards 703.5.5
- Character height based on the uppercase letter I2010 ADA Standards 703.5.5