Ronald Moravec , Jan 03, 2009; 06:58 p.m.
If you make the assunption , EOS os 24x30 so it is the same ratio as 8x10, the normal is around 38 mm. 300 divided by 38 is 7.8. Now multiply 38x 8 x 7.9 to proportion it up. Divide by 25 to convert to inches. 2400 mm or 100 inches
To get a more accurate answer, calculate the diagonal of 24x30 exactly 24x24+30x30 and find square root