Match the pattern
Select the same hole shape and row arrangement shown on the approved drawing or sample.
Engineering Tool · Perforated Metal
Perforated Metal Open Area Calculator
Calculate theoretical open area for common round, square, hexagonal, slotted and rectangular perforation patterns from opening dimensions and centre-to-centre pitch.
Quick definition: open area is the percentage of a repeating sheet surface occupied by holes. It is a geometric value—not a direct prediction of flow rate, pressure drop or filtration efficiency.
Enter perforation dimensions
Choose the pattern shown on your drawing, then enter dimensions in one consistent unit.
Round holes — 60° staggered
The densest standard round-hole layout. Pitch is measured centre to centre.
Diameter of each round opening.
Square side, hexagon width, slot width or rectangle width as shown.
Overall slot or rectangle length.
Centre-to-centre distance between adjacent holes.
Centre pitch in the second direction.
This selector changes the unit label; it does not convert entered numbers. Convert all pattern and sheet dimensions together when switching units. Open-area percentage is unchanged for equivalent dimensions.
Calculated results
Theoretical values for one repeating pattern cell.
Open area35.43%geometric opening ratio
Solid area64.57%remaining sheet ratio
Opening area19.635 mm²per repeating opening
Pattern cell area55.426 mm²formula reference cell
Formula used
OA = 90.69 × (D ÷ C)²D = hole diameter; C = equal centre pitch. Use the same unit for both.
Finished-sheet boundary adjustment
Use actual dimensions of a flat rectangular sheet to estimate open area after blank margins and a weld strip.
Use the hole pattern above. Then select the boundary layout below and enter the finished sheet dimensions.
Blank edge margins
Unperforated weld strip
Enter actual sheet, margin and weld-strip dimensions in mm, matching the unit selected above. The strip is subtracted within the area left after the margins.
Select a boundary layout to continue.
Finished-sheet estimate
- Pattern open area
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- Gross sheet area
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- Perforated region
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- Estimated hole area
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- Overall open area
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Overall open area = pattern open area × perforated region ÷ gross sheet area. This geometric estimate assumes a uniform pattern in the remaining region; partial edge rows, forming and supports are not modeled.
Choose a calculation by the required result
Pattern or a simple sheet estimate: use this page for the supported hole shapes and its optional blank-edge/weld-strip adjustment. Left/right margins reduce width; top/bottom margins reduce length.
Target percentage or extra blocked zones: use the effective sheet open area calculator for its supported round/square patterns, additional blocked-area input and reverse calculation of pitch or hole size.
Number of complete round holes: use the sheet hole count calculator. Its margins run from sheet edge to hole edge; the first hole starts at the left/top margins, with the selected row arrangement. A continuous area estimate does not place or count individual holes.
The tools share geometric assumptions where their inputs match. This page uses the rounded 90.69 coefficient for 60° round patterns; the effective-area tool uses the full π-based constant, so small numerical differences can occur.
How to use the calculator
Use centre pitch
Enter centre-to-centre spacing, not the solid ligament between adjacent hole edges.
Verify the finished part
Account for blank margins, seams, forming zones, supports and tolerances before using the result for design.
Formula applicability and limits
The calculator evaluates one ideal repeating pattern cell. Round, square and rectangular openings use geometric opening area divided by the associated pitch cell. Round-end slots use the area of the straight centre section plus two semicircular ends.
For the hexagonal mode, S and C must follow the dimensions in the displayed diagram. If your drawing defines a hexagon by side length, across-corners distance or another pitch convention, calculate from the actual repeating cell area instead.
Do not treat theoretical open area as usable flow area for a finished component. Unperforated borders, welds, overlaps, reinforcing rings, supporting mesh, blocked surfaces and formed sections can reduce the active area.
The calculator is not intended for louvres, bridge slots, countersunk holes, embossed or raised holes, decorative irregular patterns, variable pitch, nested patterns or damaged/distorted perforations.
Pattern formulas
| Pattern | Formula | Required dimensions | Important condition |
|---|---|---|---|
| Round, 60° staggered | OA = 90.69(D/C)² | D, equal pitch C | C must exceed D |
| Round, straight | OA = 78.54D²/(C1C2) | D, C1, C2 | Use centre pitches |
| Square or rectangular | OA = 100WL/(C1C2) | W, L, C1, C2 | Opening must fit the pitch cell |
| Round-end slot | OA = 100[W(L−W)+πW²/4]/(C1C2) | Overall L, W, C1, C2 | L must be at least W |
| Hexagonal diagram mode | OA = 100(S/C)² | Diagram-defined S and C | Do not substitute side length |
Frequently asked questions
What is open area in perforated metal?
It is the percentage of an ideal repeating sheet area occupied by holes. It describes geometry, not filtration efficiency or guaranteed airflow.
Why does a 60° staggered round pattern have more open area?
The triangular repeating layout packs equal round holes more closely than a straight square layout at the same diameter and pitch.
Is pitch the same as the ligament between holes?
No. Pitch is measured from the centre of one opening to the centre of the next. Ligament is the solid edge-to-edge distance.
Does sheet thickness change the open-area percentage?
Not in this two-dimensional formula. Thickness can affect punching feasibility, hole taper, burrs, pressure loss and finished performance, but not the nominal surface ratio.
Can open area be used as airflow or filtration efficiency?
No. Flow and separation performance also depend on thickness, hole geometry, fluid properties, pressure, edge conditions, downstream supports and system design.
Why can the finished component have less usable open area?
Blank margins, weld bands, overlaps, frames, supports and blocked surfaces remain solid or obstructed, reducing the actual active area.
Can I use these results as manufacturing tolerances?
No. Use them for preliminary engineering selection. Final tolerances and usable area should be confirmed on approved drawings and inspected parts.
Need a production-ready perforation specification?
Share the hole pattern, dimensions, material, thickness, margins and drawing with our engineers.
Engineering disclaimer: Use the theoretical percentage to compare supported hole patterns. Record hole dimensions, centre pitch and solid zones on the drawing, review manufacturing feasibility, and inspect the finished component. Assess flow, filtration and structural requirements with the appropriate data and model.