Signs
ADA braille dot dimensions
Table 703.3.1 in full — five measurements with their tolerances, in the standard's own inches and millimetres.
These are the numbers that decide whether a sign can be read. They are tight: the spacing between lines is fixed within five thousandths of an inch, which is why braille on signage is set by machine.
| Measurement | Inches | Millimetres | Measured |
|---|---|---|---|
| Dot base diameter | 0.059 to 0.063 | 1.5 to 1.6 | — |
| Distance between two dots in the same cell | 0.090 to 0.100 | 2.3 to 2.5 | centre to centre |
| Distance between corresponding dots in the adjacent cell | 0.241 to 0.300 | 6.1 to 7.6 | centre to centre |
| Dot height | 0.025 to 0.037 | 0.6 to 0.9 | — |
| Distance between corresponding dots from one cell directly below | 0.395 to 0.400 | 10 to 10.2 | centre to centre |
Dot base diameter
0.059 to 0.063 in (1.5 to 1.6 mm) · 703.3.1
How wide each dot is where it meets the sign. The range is narrow — four thousandths of an inch — because a dot that spreads wider than its neighbours closes the gap between them and the cell reads as a blur.
Distance between two dots in the same cell
0.090 to 0.100 in (2.3 to 2.5 mm) · 703.3.1, centre to centre
The spacing inside one cell, between dot 1 and dot 2, or dot 1 and dot 4. This is the measurement a fingertip uses to tell which of the six positions is raised, so it is the one that decides whether a sign can be read at all.
Distance between corresponding dots in the adjacent cell
0.241 to 0.300 in (6.1 to 7.6 mm) · 703.3.1, centre to centre
Dot 1 of one cell to dot 1 of the next. Note that it is corresponding dots, not the gap between the cells — measuring the blank space instead is the commonest way a correct sign gets reported as wrong.
Dot height
0.025 to 0.037 in (0.6 to 0.9 mm) · 703.3.1
How far each dot stands off the surface. The smallest figure in the table, and the one that wears away first: a dot at the bottom of the range on the day it was installed has nowhere to go.
Distance between corresponding dots from one cell directly below
0.395 to 0.400 in (10 to 10.2 mm) · 703.3.1, centre to centre
Line to line. The tightest tolerance in the table — five thousandths of an inch — which is why multi-line braille on a sign is set by machine and not by hand.
The rules that are not measurements
A sign can pass a calliper check on all five rows above and still fail the standard. These are the requirements that a measurement does not catch — and the raised text above the braille has a dimension table of its own.
| Requirement | Clause | Why it is there |
|---|---|---|
| Braille shall be contracted (Grade 2) | 703.3 | Not a preference. Uncontracted braille on an American sign does not meet the standard, however carefully it is made. |
| Dots shall have a domed or rounded shape | 703.3.1 | A flat-topped or conical dot has an edge, and an edge under a moving fingertip reads as noise. It is also the shape a router leaves, which is why it appears on signs that were cut rather than raised. |
| Braille shall be positioned below the corresponding text, and below all of it where the text runs to more than one line | 703.3.2 | So a reader who finds the raised text knows where the braille is without hunting. The predictability is the point. |
| Braille shall be separated 3/8 inch (9.5 mm) minimum from any other tactile characters and from raised borders and decorative elements | 703.3.2 | A decorative raised border closer than 3/8 inch is read as part of the braille. On elevator car controls the separation drops to 3/16 inch (4.8 mm), and the braille may sit beside the control rather than below it. |
The rule about capital indicators is long enough, and misapplied often enough, to have its own page — with the cost measured in cells.
Every dimension and rule on this page is from the 2010 ADA Standards for Accessible Design, published by the United States Department of Justice, checked against the standard's own text on every build of this site. These are the federal 2010 ADA Standards. A given project may also be under a state or local code with its own requirements — California's Title 24 is the usual example — and where they differ the stricter one generally governs. Check the standard itself before specifying a sign; every clause quoted here is linked to its source.