1. Use finished dimensions
Enter the outside diameter after forming; measure the strip on the outer developed circumference.
Engineering Tool · Perforated Tube
Perforated Tube Effective Open Area Calculator
Estimate total clear opening area and finished-tube open area, including unperforated end zones and a longitudinal weld strip.
Geometry basis: the hole-pattern percentage applies only to the perforated region. The finished-tube percentage uses the complete cylindrical outside surface.
Enter tube and hole layout
Use finished dimensions in the same selected unit.
The 60° layout assumes equal centre spacing.
Changing unit converts the entered dimensions.
Unperforated finished-tube zones
Measured along the developed circumference. Enter 0 if none.
Calculated results
Ideal repeating-pattern estimate before edge trimming.
Pattern open area—within perforated region
Finished-tube open area—of the complete outside surface
Total clear opening area—per tube, theoretical
Perforated region area—developed outer surface
Formula and basis
Surface = πDL. Perforated region = (πD − strip width) × (L − end blanks). Clear opening = region × pattern open-area fraction. Finished-tube percentage = clear opening ÷ surface × 100.
Straight rows: pattern fraction = πd²/(4CR).
How to use this calculator
2. Subtract blank zones
Enter the two unperforated ends and the weld strip width once.
3. Confirm the layout
Check edge holes, cut rows, tooling tolerance and seam position against the approved drawing.
Frequently asked questions
Is pattern open area the same as finished-tube open area?
No. The finished value includes end blanks and the seam strip in the total surface denominator.
Does this count individual holes?
No. It applies a repeating-pattern fraction. Edge holes and partial rows require the production drawing.
How is the 60° layout calculated?
Axial row pitch is C × √3/2, and the pattern fraction is πd²/(2√3C²) for equal-pitch round holes.
Does open area predict pressure drop?
No. Fluid properties, hole edges, supports and flow distribution also matter. See the Flow & Pressure Drop Calculator.
Need a perforated tube drawing?
Send the diameter, hole pattern, blank ends and seam allowance for a manufacturing review.
Contact Our EngineersEngineering note: This is an ideal developed-surface estimate, not a counted hole layout, net filtration area or guaranteed flow capacity.
