Signs
How tall the letters on a braille sign must be
Cap height is 5/8 to 2 inches, measured from the baseline on the uppercase I — with the proportion, stroke and spacing rules the standard hangs off that one letter.
Braille on an American sign never travels alone. Section 703.2 requires raised characters, and requires them to be duplicated in braille — so a sign fails just as completely for letters that are too small as for cells that are mis-spaced. The dot dimensions cover the braille half. This page is the other half: the text a sighted reader uses and a hand passes over on the way to the cells.
The phrase people search for is “cap height”. The standard never uses it. What it specifies is character height, measured on the uppercase letter I — which is the same measurement, described without the typographic jargon.
The height rule
703.2.5 Character Height. “Character height measured vertically from the baseline of the character shall be 5/8 inch (16 mm) minimum and 2 inches (51 mm) maximum based on the height of the uppercase letter ‘I’.”
EXCEPTION: “Where separate raised and visual characters with the same information are provided, raised character height shall be permitted to be ½ inch (13 mm) minimum.”
| Measurement | Inches | Millimetres | Clause |
|---|---|---|---|
| Character height, minimum | 5/8 | 16 | 703.2.5 |
| Character height, maximum | 2 | 51 | 703.2.5 |
| Minimum where separate visual characters carry the same information | 1/2 | 13 | 703.2.5 exception |
Two things are easy to get wrong here. The measurement runs from the baseline, not from the lowest ink on the sign — a descender hanging below it is not part of the height. And it is taken on the uppercase I specifically, not on whichever letter happens to be tallest.
The exception is narrower than it looks. It applies only where the same message appears twice on the sign, once raised and once visually; a single line of raised text that is also the visual text does not qualify, and 5/8 inch remains the floor.
Why the uppercase I decides everything
The I has no ascender, no descender and no curve overshooting the baseline, so its height is unambiguous in any font. Having fixed it, the standard hangs two more rules off it — one governing how wide the letters may be, one governing how heavy.
| Rule | Requirement | Clause |
|---|---|---|
| Character proportions | The width of the uppercase O is 55% minimum and 110% maximum of the height of the uppercase I | 703.2.4 |
| Stroke thickness | The stroke of the uppercase I is 15% maximum of the height of the character | 703.2.6 |
Together these three clauses rule out most display faces without naming a single one. A condensed font fails the O test; a heavy one fails the stroke test; anything with a decorative I fails both. That is the point — a finger reading a raised letter is tracing its outline, and an outline that is too narrow, too fat or too ornamented stops being traceable well before it stops being readable by eye.
The rest of 703.2
Height is the clause people look up. It is one of eight, and a sign has to pass all of them.
| Clause | Requirement |
|---|---|
| 703.2.1 Depth | Raised characters stand 1/32 inch (0.8 mm) minimum above their background |
| 703.2.2 Case | Characters are uppercase |
| 703.2.3 Style | Sans serif; not italic, oblique, script, highly decorative or of other unusual forms |
| 703.2.4 Character proportions | Uppercase O width 55% to 110% of uppercase I height |
| 703.2.5 Character height | 5/8 inch (16 mm) to 2 inches (51 mm), on the uppercase I |
| 703.2.6 Stroke thickness | 15% maximum of character height |
| 703.2.7 Character spacing | 1/8 inch (3.2 mm) minimum for rectangular cross sections, 1/16 inch (1.6 mm) minimum for others at the base — and 4 times the stroke width maximum in either case. Characters sit 3/8 inch (9.5 mm) minimum clear of raised borders and decorative elements |
| 703.2.8 Line spacing | Baseline to baseline, 135% minimum and 170% maximum of the raised character height |
Note that 703.2.7 measures spacing between the two closest points of adjacent characters, excluding word spaces — so a rounded letter beside a straight one is measured where they come nearest, not centre to centre. This is the same trap as the braille dimensions, where the spacing that matters is between corresponding dots rather than between the cells.
How this meets the braille
The two halves of the sign are bound together by one sentence: raised characters “shall be duplicated in braille complying with 703.3”. Whatever the letters say, the cells say, and the same 3/8 inch (9.5 mm) that separates characters from a raised border also separates them from the braille below.
So the full specification for a compliant tactile sign runs across three pages here: the letters on this one, the five braille dimensions in Table 703.3.1, and where the braille and the sign are positioned. The braille itself is contracted Grade 2, and capitals follow a rule of their own.
Where these figures come from
Every figure on this page is quoted from the 2010 ADA Standards for Accessible Design, published by the United States Department of Justice, section 703.2. The clause number is given beside each one so it can be read at the source rather than taken on trust from here. This page is not legal advice and it is not the standard.