Perforated Metal Open Area Calculator

Open area depends on hole shape and pattern. For round holes in 60° staggered arrangement (most common): OA% = 90.7 × d² / P². For 90° straight arrangement: OA% = 78.5 × d² / P². For square holes in straight arrangement: OA% = (w / (w + b))² × 100. Where d = hole diameter, P = center-to-center pitch, w = hole width, b = bridge (ligament) width.

60° staggered arrangement allows holes to be packed more efficiently — each hole fits in the gap between the row above. For the same hole diameter and pitch, staggered gives about 15% more open area than straight arrangement. Staggered patterns also provide better structural integrity because the metal bridges are offset.

For drainage floors and trench covers, 25–35% open area is usually sufficient. For high-flow drainage (process industries, storm drains), aim for 40–60%. For acoustic panels or air filtration, 20–30% is typical. Building codes may specify minimum open area for specific applications — always verify with local standards.

Larger holes or higher open area means less material remains, so the sheet is lighter. Weight per m² = base sheet weight × (1 − OA/100). For example, a 3mm steel sheet at 30% OA weighs 23.6 kg/m², while the same sheet at 60% OA weighs only 9.4 kg/m².

The minimum bridge (ligament) between holes is typically 1.0–1.5× the material thickness, with an absolute minimum of about 1.0mm for thin sheets. Too-thin bridges cause tearing during punching. Most manufacturers require bridges of at least 50% of hole diameter for structural integrity.

Perforated metal is available in carbon steel, galvanized steel, stainless steel 304/316, aluminum, copper, and brass. Carbon steel is most common for industrial applications. Stainless is used in food, chemical, and architectural applications. Aluminum is used where low weight and corrosion resistance are both required.

Yes — use the 'Slotted / Oblong' hole type. Enter the slot width (short dimension), slot length (long dimension), and the two pitch values (pitch perpendicular to slot × pitch parallel to slot). The formula uses an approximation based on equivalent circular area.

Perforated metal is punched — holes are stamped through a flat sheet leaving a flat surface. Expanded metal is slit and stretched — the original sheet has no material removed but is deformed into a diamond mesh pattern. Perforated tends to cost more per m² but gives cleaner, more precise hole geometry. Use our Expanded Metal Calculator for expanded metal weight.