How big should
your letters be?

The industry rule of thumb is 1 inch of letter height for every 10 feet of viewing distance. So a sign read from 100 feet away needs letters at least 10 inches tall. That figure is the maximum distance the letter is still legible — for a sign that reads comfortably at a glance, use 1 inch per 4 feet instead, which would make those same 100-foot letters 25 inches.

About 120 feet at the limit of legibility, and roughly 48 feet for comfortable, at-a-glance reading. Those numbers assume good contrast — dark letters on a light background or the reverse — in daylight, with a clear line of sight.

It is the standard legibility index used for on-premise signage: each inch of capital letter height buys about 10 feet of readable distance. It is a rule of thumb, not a building code, and it describes the point at which a letter is still just readable — not the point at which it is easy to read.

Yes, and it is the mistake most often made. A driver at 45 mph covers 66 feet every second, so a sign readable from 200 feet gives them roughly three seconds to find it, read it, and act. Longer messages need either bigger letters or fewer words — the calculator shows you the read time you actually have.

Measure the capital letter height, also called cap height. Lowercase letters without ascenders sit shorter than the capitals around them, so measuring an 'e' or an 'o' will make the sign look smaller than the numbers suggest. Script and heavily stylised faces read shorter still at distance, so size them up.

No — this is legibility, not permission. Maximum sign area, letter height and placement are set by your local sign ordinance, and they frequently allow less than the distance calls for. Check the rules for your city before you quote the job.