This shopfront has 52% glazing if the entire first floor facade is counted. For the area between 2 feet and 12 feet high, which many codes call for, the percentage of glazing here is 61%.

To measure glazing percentages on photographs:
1. Shoot the facade straight on, with no diminishing perspective. (The method will work with vertical or horizontal keystoning only if the glazing is symmetrical in the same direction as the keystoning. )
2. Using Histogram>Show Statistics, record the number of pixels in the total first floor facade, or whatever area will be regulated.
3. Select only the glazing (OK to include muntins). Press Shift to select more than one area.
4. Clear the statistics cache using the refresh symbol in the palette, then record the total of the selected pixels.
5. Divide smaller number into larger in a percentage calculator.