In this thread:
http://www.typophile.com/node/36418
James Montalbano quoted;
"As to size, I believe ADA guidelines specify 1 inch of cap height for every 50 ft of viewing distance.(I know this is what FHWA has built their spec on)."

I also remember using this guideline back in my days in the sign business. You might want to use a size larger than that formula provides, since a billboard needs to be read from a moving vehicle, which is considerably more difficult than reading while standing still.

Jason C

I would go out and study the Billboards in your area. In most cases a car driver looks at a billboard for about three seconds. With that in mind, you should keep it simple and readable. Don't put to much information on it.

Cheers!
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Fischers Fritz fischt frische Fische, frische Fische fischt Fischers Fritz.

6 seconds - 6 words
7 seconds - 7 words

An old billboard axim.

Good luck getting the client to stick to that.

pbc

http://elliott-design.net/letter_size_chart.htm

this is based on US D.O.T. standards

I just did 11 billboards for a campaign in New Jersey. 15 words. They range from 14' x 36' (signage companies always do the dimensions backwards - at least for me) to 16' x 60'.

I would estimate that the main letters (a band name in Franklin Gothic Condensed or Extra Condensed) are 8' to 14' tall (depending on the board size).

The other words are probably around 2' to 5' tall.

They are done to scale in Illustrator (1/48 to 1/12 scale depending on the vendor) so you can get there with point size. I have done them full size and then you have to set the type and scale it - 1200 points - I believe that's the limit in our software - is not large enough.

pbc