Expanded metal is made by slitting a sheet of steel and stretching it, so the diamonds you see are opened-up metal rather than holes punched out of it. Nothing is removed. That single fact explains most of its properties: it is lighter than the sheet it came from for the same coverage, it has no waste in manufacture, and the strands are work-hardened and angled, which makes it stiffer than its weight suggests. This page covers the sizes, how to read a designation, and the one specification trap that catches people ordering it.
How to Read an Expanded Metal Designation
A designation looks like 1/2-20, 3/4-22, or in some catalogs 3/4 #9. It has two parts:
| Part | Example | Meaning |
|---|---|---|
| First number | 1/2 | Short Way of Diamond (SWD), in inches |
| Second number | 20 | Gauge or weight designation; higher number means lighter, thinner material |
Here is the trap. The first number is a real dimension and means the same thing everywhere. The second number is a supplier’s weight or gauge code, and it is not standardized across the industry. One mill’s 3/4 #9 and another’s 3/4-16 may or may not be the same material. Always confirm the actual strand thickness, strand width and weight per 100 square feet rather than ordering on the code alone, particularly if you are matching existing material.
The Terminology
| Term | What it measures |
|---|---|
| SWD | Short Way of Diamond: bond to corresponding bond, across the short axis |
| LWD | Long Way of Diamond: bond to corresponding bond, across the long axis |
| SWO / LWO | The same two distances measured as the opening, between bond interiors |
| Bond | The intersection where two strands meet |
| Strand width | The amount of material fed into the press to make one strand |
| Strand thickness | On standard mesh, the gauge of the base sheet |
SWD and LWD are center-to-center style measurements taken bond to bond. SWO and LWO are the clear openings. Those are different numbers and quoting the wrong one is a common source of confusion when someone asks “will a 1/2 inch object pass through it.”
Standard Sizes and Weights
Common SWD sizes are 3/16, 1/4, 5/16, 1/2, 3/4, 1 and 1-1/2 in. Weight ranges by material, per 100 square feet:
| Material | Weight range (lb per 100 sq ft) |
|---|---|
| Standard (raised) steel | 56 to 180 |
| Flattened steel | 39 to 171 |
| Stainless steel | 35 to 137 |
| Aluminum | 14 to 43 |
A worked example, 1/2-20 in standard steel, shows how the dimensions relate:
| Property | Value |
|---|---|
| Weight | 43 lb per 100 sq ft |
| SWD | 0.5 in |
| LWD | 1.2 in |
| Opening (SWD × LWD) | 0.438 in × 0.938 in |
| Strand thickness | 0.036 in |
| Strand width | 0.072 in |
Note the relationship between the designation and the opening. The SWD is 0.5 in, exactly as the code says, but the clear opening is 0.438 in. The difference is the bond. If you need a specific clear opening, specify SWO, not SWD.
Note also that strand width here is exactly twice the strand thickness. That is not a rule, but it is typical: the slitting and stretching operation produces a strand whose cross section is roughly the sheet thickness by a somewhat wider face, and it is why expanded metal of a given weight is stiffer in bending than a flat sheet of the same weight. Base sheet thickness follows ordinary sheet steel gauge conventions.
Standard vs Flattened
This is the choice that matters most after size.
Standard, also called regular, raised or unflattened, is the mesh as it leaves the press, with strands and bonds set at a uniform angle to the plane of the sheet. The strands stand proud, which gives it grip underfoot and a visible texture, and keeps the full depth of the strand working in bending.
Flattened is standard mesh passed through a cold roll mill until the surface is smooth. The roll stretches the sheet slightly, so flattened mesh covers marginally more area for the same starting sheet, which is why the flattened weight range per 100 square feet starts lower than the standard range. The trade is that rolling the strands flat reduces the effective depth, so flattened mesh is less stiff than the standard version it came from. Choose standard for walkways, guards and anywhere grip matters; choose flattened where a smooth surface, a flush fit or a painted finish is the point.
How It Is Cut, and Why That Is on the Order
Three shearing methods exist, and they change what the edge of your sheet looks like. Random shearing cuts wherever the blade lands, leaving open, partial diamonds at the edge. Bond shearing cuts through the bonds so the edge finishes on closed diamonds. Machine-run sizing produces sheets to a set dimension off the press.
If the edges will be visible, welded into a frame, or need to be safe to handle, specify it. A random-sheared edge is a row of sharp points. Standard sheets are commonly supplied 4 ft by 8 ft, with other sizes made to order.
Specifying It Properly
A complete callout names six things: material and grade, standard or flattened, the SWD and weight designation, the sheet size, the edge or shearing treatment, and the finish. Finish matters more than people expect, because expanded metal has an enormous amount of cut edge relative to its weight, and every one of those edges is bare steel. Pre-galvanized sheet that is then expanded has unprotected strands at every slit. For anything outdoors, galvanize after expanding or specify stainless or aluminum. The reasoning is the same as in does galvanized steel rust.
One more specification point: expanded metal is directional. The diamonds are not symmetric, so stiffness differs between the two axes. If the sheet is spanning rather than simply cladding, the manufacturer’s load data will state which way to run it, and that orientation needs to be on the drawing. Where a real walking surface carrying real loads is involved, steel decking or bar grating is usually the correct product instead.
Expanded Metal FAQ
What does 3/4 #9 expanded metal mean?
3/4 in short way of diamond, in the supplier’s #9 weight. The 3/4 is a reliable dimension. The #9 is that supplier’s code, so check the strand thickness and weight per 100 sq ft against what you actually need.
Is expanded metal stronger than perforated sheet?
Generally yes, for the same base sheet, because perforating removes material and leaves a flat sheet, while expanding removes nothing and leaves angled, work-hardened strands. Perforated sheet wins on appearance, on precise open-area control and on having no directionality.
Can I walk on it?
Only on a span and thickness the manufacturer’s load table supports, properly fixed at the edges. Heavy standard-grade expanded metal is used for walkways and catwalks, but light mesh is a guard or a screen, not a floor.
What is the open area?
It varies widely with the SWD and the weight, roughly from the low tens of percent up to around 80 percent. Because it depends on both numbers in the designation, take it from the supplier’s table for the exact pattern rather than estimating.
Sources: Metalex expanded metal terminology for the definitions of SWD, LWD, SWO, LWO, bond, strand width and thickness, the standard and flattened descriptions and the three shearing methods; Russel Metals expanded metal product data for the designation format, standard SWD sizes, material weight ranges and the 1/2-20 dimensions. Last updated: October 2026.
This page is reference information only and is not engineering advice. Do not use it to size a walking surface or guard. Full disclaimer.