How Big Should Letters Be on a Sign? (Viewing Distance Chart)
A widely used sign-industry rule of thumb is about 1 inch of capital letter height for every 10 feet of viewing distance, so a sign read from 30 feet needs letters about 3 inches tall. That figure gives comfortable reading; research by the United States Sign Council (USSC) puts the average upper limit at about 30 feet per inch, and font, contrast, lighting, and all-caps text all change the result.
Sign letter height vs viewing distance chart
| Capital letter height | Comfortable reading (10 ft per inch) | Approximate upper limit (USSC average, 30 ft per inch) |
|---|---|---|
| 1 in | 10 ft | 30 ft |
| 2 in | 20 ft | 60 ft |
| 3 in | 30 ft | 90 ft |
| 4 in | 40 ft | 120 ft |
| 6 in | 60 ft | 180 ft |
| 8 in | 80 ft | 240 ft |
| 10 in | 100 ft | 300 ft |
| 12 in | 120 ft | 360 ft |
| 18 in | 180 ft | 540 ft |
| 24 in | 240 ft | 720 ft |
Comfortable reading is the distance where most people read the sign easily. The upper limit uses the USSC rule-of-thumb Legibility Index of 30, an average the USSC says may fall short for a specific font, color, or setting.
How to calculate letter height for any distance
- Comfortable reading: letter height in inches = viewing distance in feet / 10.
- USSC method: letter height in inches = viewing distance in feet / Legibility Index. The Legibility Index is the number of feet of reading distance per inch of capital letter height, and it varies with font, color, and lighting.
- All caps: the USSC adds about 15% to letter height when a message is set in all capital letters instead of upper and lower case.
Example: a storefront sign meant to be read from across a 60-foot parking lot needs letters about 6 inches tall for comfortable reading, and no smaller than about 2 inches.
ADA minimum letter height for overhead and wall signs
Directional and informational signs inside a building must meet the visual character rules in §703.5 of the 2010 ADA Standards. Table 703.5.5 sets a minimum height based on how high the sign is mounted and how close a person can get to it. Character height is measured on the uppercase I.
| Height of the character baseline above the floor | Horizontal viewing distance | Minimum character height |
|---|---|---|
| 40 in to 70 in | Less than 72 in (6 ft) | 5/8 in |
| 40 in to 70 in | 72 in or more | 5/8 in plus 1/8 in per foot beyond 6 ft |
| Over 70 in to 120 in | Less than 180 in (15 ft) | 2 in |
| Over 70 in to 120 in | 180 in or more | 2 in plus 1/8 in per foot beyond 15 ft |
| Over 120 in | Less than 21 ft | 3 in |
| Over 120 in | 21 ft or more | 3 in plus 1/8 in per foot beyond 21 ft |
Example: an overhead sign with its text 96 inches above the floor, read from 25 feet away, falls in the over 70 in to 120 in row. It is 10 feet beyond 15 feet, so it needs 2 in plus 10 x 1/8 in, or 3-1/4 inch letters at minimum. Room and restroom signs with raised characters follow a different rule: 5/8 to 2 inches tall (§703.2.5).
How big should letters be on a sign to read from 100 feet?
About 10 inches for comfortable reading, using the 1 inch per 10 feet rule. At the USSC average of 30 feet per inch, the absolute smallest would be about 3-1/2 inches, which is too small for a quick glance.
Do all-caps letters need to be bigger?
Yes. USSC legibility research found that a message set in all capital letters needs about 15% more letter height to read at the same distance as upper and lower case text.
What letter size does the ADA require on a door sign?
Raised characters on room, office, and restroom signs must be 5/8 inch to 2 inches tall, measured on the uppercase I (§703.2.5), mounted 48 to 60 inches above the floor to the baseline.
What font is most readable on a sign?
A plain, conventional font with clear letter shapes and good contrast against the background. The ADA requires visual characters to be conventional in form, not italic, oblique, script, or highly decorative (§703.5.3), and raised characters to be sans serif (§703.2.3).
Planning a sign? See custom signs and banners, our office signs guide, or office and ADA signs. Every badge and sign is made in-house in the USA by NameBadge.com, a family-owned company since 2008.
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