Perforated Sheet Hole Patterns: Round, Square, Slotted and Open Area Explained

A perforated sheet looks simple. A sheet with holes. But order one without the numbers and you will get a sheet that is either too strong or too airy, and no one at the shop will know which you meant.

Three numbers and one choice describe every perforated sheet. Learn them and you can order by phone.

The three numbers

1. Hole size (d). The diameter of a round hole, or the width of a square or slot.
2. Pitch (p). The distance between the centres of two neighbouring holes.
3. Thickness (t). The thickness of the sheet, in mm or in gauge.

Pitch is centre to centre, so a 5 mm pitch is not a 5 mm opening: the clear opening is the hole size (d). Always say which one you mean.

The solid strip between two holes is called the bridge. Pitch minus hole size gives you the bridge width. A bridge narrower than the sheet thickness makes a weak, wavy sheet.

The one choice: straight or staggered

• Straight (90 degree). Holes in neat rows and columns. Square grid look. Lower open area.
• Staggered (60 degree). Every second row is shifted half a pitch. Stronger sheet, more holes in the same area, the usual choice for round holes.

Open area: how much air or light passes

Open area is the share of the sheet that is hole. It decides airflow, light and weight.

For round holes:

• Staggered 60 degree: open area % = 90.7 × (d ÷ p)²
• Straight 90 degree: open area % = 78.5 × (d ÷ p)²

Worked example. 5 mm holes at 8 mm pitch, staggered: (5 ÷ 8)² = 0.39, so open area is about 35%.

Table scrolls sideways

Open area is not a safety rating

Open area tells you how much air or light passes. It does not tell you whether a sheet is suitable as a machine guard. A guard must meet the machine's own safety requirements for opening size and distance from the hazard. Have a competent person specify that before you order.

Which pattern for which job

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Material and thickness

• MS perforated sheet. Cost effective. Paint it if it goes outdoors.
• GI perforated sheet. Zinc coated, better for coolers, outdoor screens and damp places.
• Thickness. 0.5 to 1 mm for light panels. 1.5 to 3 mm for guards and structural screens.

Ordering by phone: what to say

"I need GI perforated sheet, 1 mm thick, 5 mm round holes at 8 mm pitch, staggered. Sheet size 8 x 4 feet. Quantity 10."

That sentence has everything the counter needs. If you do not know the pitch, send a photo of a sample with a ruler next to it.

Cut to size

A full sheet is usually 8 x 4 feet. We cut sheets down to your size, and form them into tubes and trays on request. See perforated sheets.

FAQs

What is open area in a perforated sheet?
The percentage of the sheet's surface that is holes. A higher number lets more air, light and sound through.

Staggered or straight holes?
Staggered gives a stronger sheet and more holes per area, so it is the usual choice for round holes. Straight is for a square grid look.

What size is a standard perforated sheet?
8 x 4 feet is common. Other sizes and rolls are available.

Is GI or MS perforated sheet better?
GI for outdoors and damp places. MS for indoor use or when you will paint it.

Can you make a custom hole pattern?
We stock the common patterns and can arrange others. Send us the drawing.