Letter Style and Capitalization

As a general rule, capital letters are more easily recognized, but tend to read individually. Lower case letters, on the other hand, are generally read as whole words or phrases. Sign design research designates six type styles as the most basic:

For the most part, reliance on the last four of these can be a problem. People are not used to reading these fonts for extended periods of time. Use them sparingly, if at all.

Capital and lower case letters, with the exception of script styles, are generally equally legible. As a general rule, the width of a letter’s horizontal stroke should be approximately 1/5 of its height. In choosing numerals, it is generally accepted that Roman numerals slow readers down because they are more complex and less familiar to the viewer than Aarabic numerals.

Letter Heights

If a sign is to be effective, then it must be legible at enough of a distance to help a driver respond. Generally, letters with a taller and wider “stroke” can be read from further away. These are the recommended letter heights to enable legibility at various speeds of highway traffic:

Speed of Traffic Recommended Letter Height
55 mph (88 kph) 16.5 in
50 mph (80 kph) 15 in
45 mph (72 kph) 13.5 in
40 mph (64 kph) 12 in
35 mph (56 kph) 10.5 in
30 mph (48 kph) 9 in
25 mph (40 kph) 7 in

Signs for Success Seminar Handbook, Nevada SBDC, 2001.

Letters of this height at these speeds should be legible to a driver for six seconds. However, if your business appeals mostly to tourists, they might need more reaction time because of unfamiliarity with your area. The longer the reaction time required, the greater the recommended letter height.