Perforated Sheet Open Area Calculator
Choose the hole pattern, enter the hole size and pitch in millimetres, and read the open area as a percentage. A fourth calculation turns a solid sheet weight and an open area into the net weight of the perforated sheet.
Round holes — straight pitch
Open area of the perforated field only. Unperforated borders and margins bring the whole-sheet figure down.
What this calculates
Open area is the fraction of a perforated sheet that is hole rather than metal, expressed as a percentage. It sets airflow through a screen, light and sound through a façade panel, what a sieve passes, and how much the sheet weighs after perforation. Designers specify it; perforators achieve it with a hole size and a pitch.
The page runs three patterns. Round holes on a straight pitch, where every hole sits on a square grid. Round holes on a 60° staggered pitch, the most common perforation pattern, where each row is offset half a pitch and the holes pack closer. Square holes on a straight pitch. Each pattern has its own formula in the engine; you choose the one your drawing calls for.
The fourth calculation is net weight: enter the weight of the solid sheet, from the sheet and plate calculator, and the open area, and the engine removes that share of the metal. It is the figure that goes on a perforation enquiry alongside the pattern.
Show the formula and a worked example
The formula
- round holes, straight pitch: OA = π × d² ÷ (4 × p²) × 100
- round holes, 60° staggered: OA = π × d² ÷ (2 × √3 × p²) × 100
- square holes: OA = (a ÷ p)² × 100
- net weight: W = solid sheet weight × (1 − OA ÷ 100)
Dimensions in millimetres, density ρ in kg/m³ — as the engine runs them.
For round holes on a straight pitch each unit cell is a square of side p holding one hole of area π × d² ÷ 4, so open area is π × d² ÷ (4 × p²) × 100. On a 60° staggered pitch the unit cell is a rhombus of area p² × √3 ÷ 2 holding the same hole, so open area is π × d² ÷ (2 × √3 × p²) × 100, about 15 % higher for the same hole and pitch.
Square holes of side a on a straight pitch give (a ÷ p)² × 100, the simplest of the three. In every case the figure is for the perforated field alone: unperforated borders, margins and the blank strips around fixings reduce the average over the whole sheet.
The engine refuses a hole that is not smaller than the pitch, because the holes would overlap and the sheet would not exist. Net weight is solid weight × (1 − open area ÷ 100), and it refuses an open area outside 0 to 100 %.
Worked example
| Calculation | Round holes — 60° staggered |
|---|---|
| Hole diameter | 5 mm |
| Pitch | 8 mm |
| Theoretical result | 35.43 % |
Computed by the calculation engine from these inputs at render time, rounded only for display.
Frequently asked
- 01What open area is typical?
- Screens and filters run from 20 % to 50 %; decorative and acoustic panels commonly sit between 10 % and 40 %; heavy-duty crusher screens go higher. The perforator's tooling sets which hole and pitch combinations are available, so a target open area is usually met with the nearest standard pattern.
- 02Why does the staggered pattern give more open area?
- Because the holes pack more tightly. Offsetting alternate rows by half a pitch fits the same holes into a smaller cell, so more of the sheet is hole. It is also the stronger pattern for a given open area, which is why it is the usual default.
- 03Does the calculator include the sheet borders?
- No. It calculates the perforated field. A sheet with a 25 mm blank margin on every side has a lower whole-sheet open area than the pattern figure. State the margins on the enquiry and the drawing.
- 04How do I get the solid sheet weight for the net weight calculation?
- Run the sheet and plate weight calculator with the sheet dimensions, thickness and grade, then bring that figure here with the open area. The result is the theoretical weight of the perforated sheet.