When working with sheet metal—whether for automotive parts, construction, or consumer goods—understanding sheet metal thickness standards and the gauge system is non-negotiable. The gauge system uses a counterintuitive, nonlinear scale (smaller numbers = thicker metal) that can confuse even experienced engineers. This guide breaks down how the gauge system works, provides detailed comparison tables for 7 common metals (steel, aluminum, copper, and more), shares real-world application examples, and answers critical questions to help you choose the right thickness for your project.
First: What Is the Sheet Metal Gauge System?
Unlike the metric system (which measures thickness directly in millimeters), the sheet metal gauge system is a historical standard based on weight per square foot of metal. This means:
- The smaller the gauge number, the thicker the metal (e.g., 3 gauge steel = 6.07mm thick; 38 gauge steel = 0.15mm thick).
- Gauge standards vary by metal type (e.g., 10 gauge steel is thicker than 10 gauge aluminum)—density differences cause this variation.
Key Thickness Limits for “Sheet Metal”
By industry standard, metal is classified as “sheet metal” only if its thickness falls within a specific range:
- Lower limit: 0.5mm (thinner than this is considered foil, not sheet metal).
- Upper limit: 6mm (thicker than this is classified as “plate metal” and follows different standards).
Note: Regional variations exist—some countries consider 8mm the upper limit for sheet metal. Always confirm with your supplier if working on international projects.
Sheet Metal Gauge Comparison Tables (By Metal Type)
Below are detailed gauge-to-thickness conversion tables for the 7 most commonly used metals in sheet metal processing. All measurements include both inches and millimeters for global compatibility.
1. Standard Steel Gauge Table
Standard steel (mild steel) is used for structural parts, brackets, and machinery components. Its gauge scale is the most widely referenced in manufacturing.
| Gauge | Thickness (in) | Thickness (mm) | Best Use Case |
|---|---|---|---|
| 3 | 0.239 | 6.073 | Heavy structural beams, industrial machinery frames |
| 4 | 0.224 | 5.695 | Large storage tanks, heavy-duty brackets |
| 5 | 0.209 | 5.314 | Truck bed floors, construction supports |
| 8 | 0.164 | 4.176 | Metal doors, safety barriers |
| 10 | 0.135 | 3.416 | Load-bearing brackets, automotive chassis parts |
| 12 | 0.105 | 2.657 | HVAC ductwork, metal shelving |
| 16 | 0.060 | 1.519 | Electrical enclosures, light-duty brackets |
| 20 | 0.036 | 0.912 | Thin metal panels, decorative trim |
| 30 | 0.012 | 0.305 | Precision electronics components, thin covers |
| 38 | 0.006 | 0.152 | Ultra-thin parts (rarely used for structural needs) |
2. Galvanized Steel Gauge Table
Galvanized steel has a zinc coating for corrosion resistance, making it ideal for outdoor or wet environments. Its gauge thickness includes the zinc layer (adds ~0.1mm to base steel thickness).
| Gauge | Thickness (in) | Thickness (mm) | Best Use Case |
|---|---|---|---|
| 8 | 0.168 | 4.270 | Outdoor fences, garden sheds |
| 10 | 0.138 | 3.510 | Roofing panels, gutter systems |
| 12 | 0.108 | 2.753 | Outdoor furniture frames, mailboxes |
| 16 | 0.064 | 1.613 | Ventilation grilles, outdoor light fixtures |
| 20 | 0.040 | 1.006 | Thin roofing flashing, decorative outdoor trim |
3. Stainless Steel Gauge Table
Stainless steel (304/316 grades) is corrosion-resistant and used for medical devices, food processing equipment, and marine parts. It has a wider gauge range than standard steel.
| Gauge | Thickness (in) | Thickness (mm) | Best Use Case |
|---|---|---|---|
| 000 | 0.375 | 9.525 | Marine hull components, heavy-duty food processing tanks |
| 3 | 0.250 | 6.350 | Industrial kitchen equipment, large chemical containers |
| 8 | 0.172 | 4.366 | Stainless steel sinks, countertop supports |
| 12 | 0.109 | 2.779 | Medical device housings, food conveyor belts |
| 16 | 0.063 | 1.588 | Cutlery, small kitchen appliances |
| 20 | 0.038 | 0.953 | Thin stainless steel panels, electronics enclosures |
| 30 | 0.013 | 0.318 | Precision medical instruments, small sensor housings |
4. Carbon Steel Gauge Table
Carbon steel (high-carbon) is stronger than standard steel but less corrosion-resistant. It’s used for tools, springs, and high-strength parts.
| Gauge | Thickness (in) | Thickness (mm) | Best Use Case |
|---|---|---|---|
| 3 | 0.239 | 6.07 | Heavy-duty tool bases, industrial springs |
| 8 | 0.164 | 4.18 | Metal cutting tools, machinery gears |
| 10 | 0.134 | 3.42 | Automotive suspension parts, high-strength brackets |
| 16 | 0.060 | 1.52 | Small tool components, thin springs |
5. Aluminum Sheet Gauge Table
Aluminum is lightweight (1/3 the weight of steel) and corrosion-resistant, making it ideal for aerospace, automotive, and consumer goods. Its gauge scale is thinner than steel for the same number.
| Gauge | Thickness (in) | Thickness (mm) | Best Use Case |
|---|---|---|---|
| 6 | 0.162 | 4.115 | Aircraft structural parts, heavy aluminum frames |
| 10 | 0.102 | 2.588 | Automotive body panels, aluminum ladders |
| 16 | 0.051 | 1.290 | Laptop casings, beverage cans (thinner grades) |
| 20 | 0.032 | 0.813 | Smartphone frames, thin aluminum sheets for signage |
| 30 | 0.010 | 0.254 | Ultra-thin aluminum foil (for packaging, not structural use) |
6. Copper Sheet Gauge Table
Copper is highly conductive and malleable, used for electrical wiring, plumbing, and decorative applications. Its gauge scale is thicker than aluminum but thinner than steel for the same number.
| Gauge | Thickness (in) | Thickness (mm) | Best Use Case |
|---|---|---|---|
| 7 | 0.180 | 4.572 | Heavy copper pipes, industrial electrical busbars |
| 10 | 0.134 | 3.404 | Medium-duty plumbing pipes, decorative copper panels |
| 16 | 0.065 | 1.651 | Electrical wiring insulation, thin copper sheets for crafts |
| 24 | 0.022 | 0.559 | Precision electrical components, decorative trim |
7. Brass Sheet Gauge Table
Brass (copper-zinc alloy) is corrosion-resistant and has an attractive gold-like finish. It’s used for decorative parts, musical instruments, and plumbing fittings.
| Gauge | Thickness (in) | Thickness (mm) | Best Use Case |
|---|---|---|---|
| 7 | 0.144 | 3.665 | Musical instrument bells, heavy brass fixtures |
| 10 | 0.102 | 2.588 | Decorative wall panels, brass hardware |
| 16 | 0.051 | 1.291 | Small brass fittings, jewelry components |
| 24 | 0.020 | 0.511 | Thin brass sheets for engraving, decorative trim |
How to Choose the Right Sheet Metal Thickness (Step-by-Step)
Selecting the correct thickness isn’t just about gauge numbers—it depends on your project’s load, environment, and manufacturing process. Follow these 4 steps:
Step 1: Define Load Requirements
- Heavy load (e.g., structural beams, truck beds): Choose 3–10 gauge (4–6mm thick) steel or aluminum.
- Medium load (e.g., shelves, brackets): Choose 12–16 gauge (1.5–2.7mm thick).
- Light load (e.g., decorative trim, electronics enclosures): Choose 18–24 gauge (0.7–1.2mm thick).
Example: A construction company needed brackets for a 500kg load. They chose 8 gauge steel (4.18mm thick)—12 gauge (2.66mm) would have bent under the weight.
Step 2: Consider Environmental Conditions
- Outdoor/wet environments: Use galvanized steel (10–16 gauge) or stainless steel (12–20 gauge) for corrosion resistance.
- Indoor/dry environments: Standard steel (12–20 gauge) or aluminum (16–24 gauge) works—cheaper than corrosion-resistant metals.
Case Study: A garden furniture maker switched from standard steel (16 gauge) to galvanized steel (16 gauge) for outdoor chairs. The galvanized chairs lasted 5 years (vs. 2 years for standard steel) without rusting.
Step 3: Match Thickness to Manufacturing Process
- CNC Machining: Thicker metal (8–12 gauge) is easier to machine—thin metal (20+ gauge) bends during cutting.
- Bending/Forming: Medium thickness (16–20 gauge) is ideal—too thick (8–12 gauge) cracks when bent; too thin (24+ gauge) warps.
- Welding: Thicker metal (10–16 gauge) creates stronger welds—thin metal (20+ gauge) burns through during welding.
Tip: For parts that need both bending and welding (e.g., metal frames), 16 gauge steel is the sweet spot.
Step 4: Use the Gauge Comparison Table to Verify
Once you’ve narrowed down your needs, cross-check with the appropriate gauge table. For example:
- Need a lightweight, corrosion-resistant part for a laptop casing? Use 20 gauge aluminum (0.813mm thick) from the aluminum gauge table.
- Need a heavy-duty structural part for a truck? Use 8 gauge standard steel (4.176mm thick) from the standard steel table.
Common Myths About Sheet Metal Gauge (Debunked)
Myths about the gauge system lead to costly mistakes. Here are 3 common misconceptions:
Myth 1: “All metals use the same gauge scale.”
Fact: Gauge varies by metal density. A 10 gauge steel sheet (3.416mm) is thicker than a 10 gauge aluminum sheet (2.588mm)—aluminum is less dense, so the same gauge number corresponds to a thinner thickness. Always use the metal-specific gauge table.
Myth 2: “Thicker metal is always more corrosion-resistant.”
Fact: Thickness only affects how long metal takes to corrode—not if it corrodes. A thin stainless steel sheet (20 gauge, 0.953mm) is more corrosion-resistant than a thick standard steel sheet (8 gauge, 4.176mm) because stainless steel has chromium, which prevents rust.
Myth 3: “Gauge is more accurate than metric thickness.”
Fact: Metric thickness (mm) is a direct measurement—gauge is a historical weight-based standard with slight variations between suppliers. For critical parts (e.g., medical devices), specify thickness in millimeters and gauge to avoid confusion.
Yigu Technology’s Perspective on Sheet Metal Thickness & Gauge
At Yigu Technology, we help clients navigate the gauge system to avoid costly errors. For structural parts, we recommend referencing the standard steel or stainless steel gauge tables and prioritizing thickness over gauge number. For lightweight or corrosion-sensitive projects, we guide clients to aluminum or galvanized steel, using their specific gauge tables to find the right balance of strength and weight. We also provide sample pieces of different gauges, so clients can see and test thickness before full production. For us, the gauge system is a tool—but the goal is always to match thickness to your project’s unique needs, not just follow a number.
FAQ About Sheet Metal Thickness Standard & Gauge
1. Can I use a steel gauge table for aluminum parts?
No—aluminum has a different gauge scale than steel. A 10 gauge steel sheet (3.416mm) is thicker than a 10 gauge aluminum sheet (2.588mm). Using the wrong table will result in a part that’s too thin (if you use steel gauge for aluminum) or too thick (if you use aluminum gauge for steel).
2. What’s the difference between “sheet metal” and “plate metal”?
Sheet metal has a thickness of 0.5–6mm (gauge 38 to gauge 3). Plate metal is thicker than 6mm (no standard gauge) and is used for heavy-duty applications like bridges or ship hulls. Always confirm if your project requires sheet or plate metal—using plate metal when sheet metal works wastes money.
3. How do I convert gauge to millimeters if I don’t have a table?
For most metals, you can use a general rule (but always verify with a metal-specific table):
- Steel: Gauge 10 = ~3.4mm, gauge 16 = ~1.5mm, gauge 20 = ~0.9mm.
- Aluminum: Gauge 10 = ~2.6mm, gauge 16 = ~1.3mm, gauge 20 = ~0.8mm.
For critical parts, never rely on estimates—use the official gauge tables provided in this guide.