Open Area Table
 
The table below provides a quick way to determine the percentage of open area for various round hole configurations. However, for a more accurate calculation, you can use the formulas to the right.
 
Diameter of hole divided by centers Round holes
60 degrees staggered
Round holes straight line Side of square divided by centers Square holes straight or staggered





D/C
% Opening
 % Opening
  S/C
% Opening
0.200 3.6 3.1 0.200 4.0
0.225 4.6 4.0 0.225 5.1
0.250 5.7 4.9 0.250 6.3
0.275 6.9 5.9 0.275 7.6
0.300 8.1 7.1 0.300 9.0
0.325 9.6 8.3 0.325 10.6
0.350 11.1 9.6 0.350 12.3
0.375 12.8 11 0.375 14.1
0.400 15.5 12.6 0.400 16.0
0.425 16.4 14.2 0.425 18.1
0.450 18.4 15.9 0.450 20.3
0.475 20.5 17.7 0.475 22.6
0.500 22.7 19.6 0.500 25.0
0.525 25.0 21.6 0.525 27.6
0.550 27.4 23.8 0.550 30.3
0.575 3.0 26.0 0.575 33.1
0.600 32.7 28.3 0.600 36.0
0.625 35.4 30.7 0.625 39.1
0.650 38.3 33.2 0.650 42.3
0.675 41.3 35.8 0.675 46.6
0.700 44.4 38.5 0.700 49.0
0.725 47.7 41.3 0.725 52.6
0.750 51.0 44.2 0.750 56.3
0.775 54.4 47.2 0.775 60.0
0.800 58.0 50.3 0.800 64.0
0.825 61.7 53.5 0.825 68.0
0.850 65.5 56.7 0.850 73.3
0.875 69.5 60.1 0.875 76.6
0.900 73.5 63.6 0.900 81.0
0.925 77.6 67.2 0.925 85.6
0.950 81.9 70.9 0.950 90.3
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Equations for calculating Open area, where:
D = the diameter of the hole;
S = side of square;
C = hole centers

 
For 60 degree staggered round holes:
 

 
For straight round holes:
 
 

 
For square holes: