A Brief History of Metal Gauge Systems
Metal gauge systems are used to describe the thickness of sheet metal — but not all metals follow the same standard. Steel, aluminium, copper, and zinc each use different gauge systems developed over time. This guide explains how they differ, and why millimetres are the best way to measure metal accurately.
Steel and Stainless Steel: BWG and AWG
The Birmingham Wire Gauge (BWG) system was one of the first used in industrial Britain. It was originally created for wire thickness, then adopted for sheet steel as manufacturing expanded.
Read more on the Birmingham Gauge system
The American Wire Gauge (AWG) developed independently in the U.S., primarily for electrical wires, but is sometimes used in sheet metals.
Learn about AWG on Wikipedia
As steel became essential to modern infrastructure, consistent sizing remained a challenge across regions.
The role of steel in infrastructure (World Steel Association)
Copper and Brass: SWG
In the UK, Standard Wire Gauge (SWG) was introduced for copper and brass used in electrical, plumbing, and decorative applications.
Explore the SWG system on Wikipedia
While SWG is still in use, it doesn’t align with BWG or AWG — so switching between materials can cause confusion.
Looking for copper or brass sheet?
Browse our brass range
Browse our copper products
Aluminium: A Modern Material with Metric Sizing
Aluminium came into wide use in the 20th century, especially in aviation and construction. Unlike older materials, aluminium sheets are more often measured directly in millimetres (mm), not gauge.
Some international suppliers still use approximate gauge conversions, but these vary — so always check the mm thickness.
Zinc: The Reverse Gauge System
Zinc takes a different approach: in its system, higher gauge numbers mean thicker sheets — the opposite of steel, copper, or aluminium.
This is due to traditional zinc production methods in roofing and cladding, especially in Europe.
See our guide to zinc gauges on Metalsheets
Why Millimetres Are Better Than Metal Gauge Systems
Because there’s no universal conversion between gauge systems, relying on gauge numbers alone can result in ordering the wrong thickness — especially when working across multiple metals.
We strongly recommend ordering by millimetre (mm) thickness for accuracy.
Related Pages
Frequently Asked Questions – Metal Gauge Systems
Why are metal gauge numbers inconsistent across materials?
Different gauge systems evolved independently for steel, copper, aluminium, and zinc. That’s why 18 gauge steel is a different thickness than 18 gauge aluminium or brass.
Can I convert gauge to millimetres?
Yes, but each gauge system has its own conversion table. The same gauge number won’t mean the same mm thickness across all metals.
Which gauge system should I use when ordering sheet metal?
We always recommend specifying thickness in millimetres (mm) to avoid confusion. It’s the most accurate and universal format.
