Perforated sheet gets specified like this:
1/4″ Hole on 3/8″ Staggered – .063″ Thick
Most people read the first number and stop. That is the hole. Fine. But the number that actually determines whether the sheet does its job is the second one — and it is the one nobody asks about.
What Each Part Means
- 1/4″ Hole — the diameter of each hole.
- on 3/8″ — the centre-to-centre distance between neighbouring holes. Not the gap between them; centre of one to centre of the next.
- Staggered — the holes sit in offset rows, in a 60° triangular grid. The alternative is straight, where they line up in square rows and columns.
- .063″ Thick — the gauge of the sheet itself. Nothing to do with the holes.
So "1/4″ on 3/8″" means quarter-inch holes with three-eighths of an inch between their centres, leaving 1/8″ of solid metal between hole edges.
Open Area Is The Real Spec
Open area is the percentage of the sheet that is hole rather than metal. It is what governs airflow, drainage, light transmission, sound absorption, and how much strength is left in the panel.
And it depends on the ratio of hole size to centre distance — not on hole size alone:
- Staggered (60°): open area ≈ 90.69 × (hole ÷ centre)²
- Straight (square): open area ≈ 78.54 × (hole ÷ centre)²
Here is what that produces across patterns we actually stock:
| Hole | On centres | Pattern | Hole ÷ centre | Open area |
|---|---|---|---|---|
| 1/16″ | 1/8″ | staggered | 0.500 | 23% |
| .050″ | 5/64″ | staggered | 0.640 | 37% |
| 1/4″ | 3/8″ | staggered | 0.667 | 40% |
| 3/8″ | 9/16″ | staggered | 0.667 | 40% |
| .050″ | .066″ | straight | 0.758 | 45% |
| 1/2″ | 11/16″ | staggered | 0.727 | 48% |
Two things in that table are worth stopping on.
Look at rows three and four. A 1/4″ hole and a 3/8″ hole — half again as big — land on exactly the same 40% open area, because both sit at a 0.667 ratio. Hole size on its own tells you nothing about throughput.
Now look at the top and bottom rows. 23% versus 48%. The bottom sheet passes more than twice as much air as the top one. Both are "perforated aluminum." If you order by hole size and hope, this is the range you are gambling across.
Staggered Or Straight?
Compare the two coefficients: 90.69 against 78.54. At the same hole-to-centre ratio, a staggered pattern gives you roughly 15% more open area than a straight one, because offset rows pack holes closer without thinning the metal between them.
Staggered is the default for that reason, and it is stronger in both directions since no continuous line of holes runs across the sheet. Straight patterns get chosen when the look matters — a visible grid reads as deliberate, which is why you see it on architectural panels and equipment fascias.
Which Number To Give Us
If you are filtering or screening by particle size, the hole diameter is what matters. Say the hole.
If you are moving air, water, light, or sound, open area is what matters. Tell us the percentage you need, or just tell us the job, and we will find a pattern that hits it.
If you are guarding a machine or a walkway, the maximum opening is usually set by a standard rather than by preference — hole size governs, and the thickness needs to carry the load.
If it is architectural, you are choosing on appearance and on how much you can see through at an angle. Get a sample and hold it up. We send those free.
Do The Math Yourself
Our opening and open-area calculator will work it out, or use the formulas above. If you want to check them: a 1/4″ hole on 3/8″ staggered centres is 90.69 × (0.25 ÷ 0.375)² = 40.3%, which is what our product pages state.
Frequently Asked Questions
Does "on 3/8 inch" mean the gap between holes?
No — it is centre to centre. With 1/4″ holes on 3/8″ centres, the solid metal between hole edges is 1/8″.
Which pattern gives more airflow?
Staggered, by roughly 15% at the same hole-to-centre ratio.
Does thickness change open area?
No. Thickness affects strength, weight, and cost, and it limits how small a hole can be punched — but the open-area percentage comes only from hole size and spacing.
How small a hole can you punch in a given thickness?
As a rule of thumb the hole diameter should be at least the material thickness. Ask us before specifying very fine holes in heavy stock.
Is perforated or woven mesh better for fine screening?
Woven, generally — it reaches far finer openings. See expanded metal vs. perforated metal, and how mesh count works if you are comparing against woven.
Tell Us The Job
We stock perforated aluminum and steel in Hayward and cut it to your dimensions. Tell us the opening or the open area you need — or just what the panel has to do — and we will spec it.
Request a quote, order a free sample, or call (510) 887-8787.