Sign Letter Size Reading Time

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This sign letter chart was created to help you determine an appropriate letter size for your particular location. Whether your sign has an LED Display or a Changeable Copy message center the same rules can be applied. The Duration of Readability chart calculates two key factors: letter size and vehicle speed. The Times in Seconds assumes that a 1” letter is readable at 50 feet. Each 1” increase in size results in an additional 50 feet of readability. However, based on industry studies, the 50 foot per inch readability criterion is generous.

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The chart below assumes free-flowing traffic. Traffic lights, stop signs, and other conditions can, in some cases, justify smaller character heights.



Remember, the figures in the chart represent the time from which letters first become readable until one passes by the sign. The need to monitor traffic conditions and normal driving concerns restrict the amount of time a driver can dedicate to reading your message. The answer, whenever possible, is to allow the driver more time to read the message through larger letter sizes.

The primary purpose of an effective sign is readability. If a sign cannot be read, then the message it carries is silenced. This letter chart will help you choose the best letter size to use for the speed of traffic passing by your sign.


From years of study, it has been determined that the recommended minimum reading time is 5 seconds.


Imagine you are the driver passing your sign. At your speed, what size letter will your sign require to allow for sufficient readability of your particular message before you have driven passed it?


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