Most sign problems come down to one question nobody asked at the start: where will people be standing when they read it? A driver at 40 miles an hour, a pedestrian across the street and a visitor in a lobby need very different letter heights, and a sign that works for one can fail for the others.
Gogi Signs designs and builds signs for storefronts, offices and buildings across New Jersey and New York City from our shop in Linden, and we size every one from the street, not from the wall. This guide gives the industry letter height chart, explains the legibility index behind it, walks through the method the United States Sign Council uses for drivers, and shows what changes for pedestrians, lit signs and interiors.
In this guide
The Letter Height Chart
The chart below is the one used across the sign industry, published by Signazon and Signs Now among others. The rule of thumb behind it is simple: every inch of letter height gives about 10 feet of viewing distance with the best impact, and the sign stays readable to a larger distance beyond that.
| Letter height | Best impact | Maximum readable |
|---|---|---|
| 3 inches | 30 feet | 100 feet |
| 4 inches | 40 feet | 150 feet |
| 6 inches | 60 feet | 200 feet |
| 8 inches | 80 feet | 350 feet |
| 10 inches | 100 feet | 450 feet |
| 12 inches | 120 feet | 525 feet |
| 18 inches | 180 feet | 750 feet |
| 24 inches | 240 feet | 1,000 feet |
| 36 inches | 360 feet | 1,500 feet |
| 48 inches | 480 feet | 2,000 feet |
Those are planning figures for a clean, high contrast sign in daylight. The next section explains where they come from and why the real answer moves.
The Legibility Index in Plain Terms
The legibility index is the number of feet of viewing distance you get per inch of letter height. The United States Sign Council Foundation’s best practice standards use 30 as the average standard, which means a 10 inch letter is legible from about 300 feet, and they cut it to about 25 in moderately busy areas and 20 in highly congested ones. That’s why the “best impact” column above is the conservative end of the range.
The index changes with the sign itself. A Signs of the Times summary of the USSC research puts the range from about 20 for a serif face in all capitals lit from outside, up to 38 for a clean sans serif in upper and lower case in neon. All capitals need about 15 percent more height than mixed case to read from the same distance. The Federal Highway Administration uses the same idea for road signs and notes that 30 feet per inch matches 20/40 vision, which is a sensible floor for any sign older drivers have to read.
Start From Where People Need to Read It
For Drivers
A driver has to notice the sign, read it and make a maneuver, all while moving. The USSC method works backward from that. Viewer reaction time is about 8 seconds on a simple road and 10 to 11 seconds in a complex or multi lane setting. Multiply the speed by 1.47 to get feet per second, then by the reaction time, and you have the distance the sign must be readable from.
Take a storefront on a four lane New Jersey highway posted at 40 miles an hour. 40 times 1.47 is 59 feet per second. With a 9 second reaction time, the sign has to be readable from about 530 feet. Divide by an index of 30 and you need letters about 18 inches tall. Drop the index to 25 for a busy commercial strip and it becomes 21 inches. That’s a very different sign from the 10 inch letters a quick look at the chart would suggest.
Drivers also only detect signs within a cone of about 10 degrees either side of straight ahead, according to the same USSC standards, which is why placement matters as much as size. Our guide to exterior sign placement covers that side.
For Pedestrians
Pedestrians read from much closer and have time. On a downtown sidewalk in a town like Jersey City, the main reading distances are about 5 to 10 feet for someone walking past, 15 to 25 feet across a wide sidewalk, and 40 feet or more from across the street. Letters of 3 to 6 inches cover the first two, and 6 to 8 inches reach across the street. Our sister shop in New York uses the same distances in its guide to sizing a storefront window poster.
A blade sign that projects from the wall is read along the sidewalk, often from 50 to 100 feet, so its letters usually need to be 6 to 10 inches even though the sign itself is small.
Inside Buildings
Interior signs are read from a few feet. The ADA Standards set the minimum for visual characters by viewing distance and mounting height: 5/8 inch for signs mounted between 40 and 70 inches and read from under 6 feet, with 1/8 inch added for every foot beyond that, and 2 inches for signs mounted higher and read from under 15 feet. A lobby sign read from 20 feet across a reception area looks right at 3 to 4 inch letters. Our guide to ADA sign requirements covers the full rules for room and wayfinding signs.
Adjust for the Real Conditions
The chart assumes daylight and high contrast. Four things move the answer:
- Lighting. The Penn State study for the USSC Foundation found that light letters on a dark background outperformed dark on light for both recognition and legibility, with the biggest difference at night, and that signs lit from outside by floodlights performed worst. If the sign has to work after dark, light it from within and keep it light on dark. Our guide to illuminated vs non illuminated signs weighs the options.
- Contrast and color. The same study found that in daylight, yellow on green and white on black read best. Low contrast pairs lose distance fast. See our guide on how color affects sign visibility.
- Typeface and case. Open sans serif faces in mixed case read furthest. All capitals, condensed faces and scripts need more height. Our typography tips for readable signs go through the details.
- Angle and obstructions. A sign parallel to traffic is read at an angle. The USSC puts the useful viewing angle at 30 to 60 degrees, and parked cars, trees and awnings cut the distance further.
Letter Height Is Not Sign Size
A sign with 18 inch letters is not an 18 inch sign. Once the letter height is set, the message length, the logo and the breathing room around the letters decide the overall size. The Sign Research Foundation recommends a stroke width about one fifth of the letter height for maximum readability, and the USSC method adds the negative space around the characters to the letter area to size the panel. Short messages are the easiest way to keep a sign readable: the business name at full height, and the tagline, if any, at half.
Our guide to choosing the right size for your business sign takes the letter height from this post and turns it into a sign size that fits the building and the town’s limit.
Matching Sign Types to Distances
| Where it is read from | Typical distance | Letter height | Sign types that fit |
|---|---|---|---|
| Highway or arterial road | 300 to 600 feet | 12 to 24 inches or more | Lit channel letters, large light box |
| Parking lot or local street | 100 to 300 feet | 8 to 12 inches | Channel letters, light box, awning graphics |
| Sidewalk and across the street | 10 to 60 feet | 3 to 8 inches | Blade sign, awning, window lettering, hand painted sign |
| Entrance and vestibule | 5 to 20 feet | 2 to 4 inches | Door lettering, dimensional letters, directory |
| Inside, at the sign | 1 to 6 feet | 5/8 to 2 inches | ADA room signs, wayfinding, egress maps |
In New York City the same logic applies, but the Zoning Resolution caps the overall sign area and height on most commercial streets, so the letter height you need has to fit inside a sign the city allows. Our guide to local sign regulations explains how to read those limits.
How to Work Out Your Letter Height
- Find the critical viewing point. The spot where someone decides to turn in, cross the street or walk in.
- Measure the distance. For drivers, use speed times 1.47 times reaction time. For pedestrians, pace it out.
- Pick the index. 30 for a clean sign on an open road, 25 for a busy strip, 20 for a congested downtown.
- Divide. Distance in feet divided by the index gives letter height in inches. Add 15 percent for all capitals.
- Check it. Against the town’s size limit, the sign band on the building and the lease. Then mock it up at full size and look at it from the viewing point.
We do this on every site survey. Pixel Wraps, our sister graphics shop, applies the same thinking to moving signs in its guide to designing vehicle graphics people can read in traffic.
Common Questions About Sign Viewing Distance
How tall should letters be to read from 100 feet?
About 4 inches for maximum readable distance and 10 inches for best impact, using the industry chart. For a driver who has to react, use the USSC index: 100 feet divided by 30 is just over 3 inches, so 4 inches is a sensible minimum and 10 inches is comfortable.
What is the 10 feet per inch rule?
A rule of thumb that every inch of letter height gives about 10 feet of viewing distance at best impact. A 12 inch letter reads well at 120 feet and remains readable to about 525 feet for a sharp eyed viewer in good light.
Do drivers need bigger letters than pedestrians?
Yes, by a lot. A driver at 40 miles an hour needs the sign readable from about 500 feet to react, which means 18 inch letters or more. A pedestrian across the street needs 6 to 8 inches.
Does a lit sign read from further away?
At night, yes. The Penn State study for the USSC Foundation found internally lit, light on dark signs had the longest legibility distances after dark, while signs lit by external floodlights performed worst.
What if the town will not allow letters as big as I need?
Shorten the message, switch to mixed case in an open sans serif, raise the contrast and light the sign. Each one buys back distance without adding height. Placement closer to the viewing point helps too.
Size Your Sign for the Real Street
Send us a photo of the building and tell us where your customers come from, and we’ll work out the letter height from the viewing point, check it against the town’s rules and mock it up at full size before anything is built. Request a free quote or see our sign design page for how the process works.
Sources and further reading
- Signazon: sign letter height visibility chart
- Signs Now: your sign visibility guide
- Penn State Transportation Institute for the USSC Foundation: sign legibility, the impact of color and illumination
