Sheet Metal Gauge Chart
The definitive guide to sheet metal gauges, thicknesses (mm & inches), weights, uses and buying tips — by Huaxiao-Alloy
Quick answer: “18 gauge” commonly refers to ~1.21 mm for steel and 1.02 mm for aluminum, but gauge values vary by material. Use the charts below for precise conversions and ordering guidance.
- September 11, 2025
- 9:38 pm
- 2076
Why this guide matters (and who it’s for)
If you design, buy, fabricate or sell metal parts you already know gauge matters. But “gauge” is often confusing:
The same gauge number means different thicknesses for steel, stainless, galvanized and aluminum.
Shops quote gauges, engineers want millimeters/inches and weights.
Wrong assumptions on gauge → wrong fit, wrong strength, wrong cost.
This guide gives you a complete sheet metal gauge chart, conversion tables, weight calculations, and practical guidance so you can order accurately and avoid mistakes. If you want to skip to buying: contact Huaxiao-Alloy at [email protected] or WhatsApp +1 (579) 300-2733 — we supply coils, sheets and cut-to-size parts worldwide.
1. What “gauge” means for sheet metal
Gauge is an older, non-metric system used to express thickness of thin metal sheets. Important facts:
For sheet metal, gauge numbers work inversely: lower gauge → thicker metal.
There are different gauge standards historically (USS, BWG, SWG) but the most used for sheet metal in North America is the U.S. standard.
Crucially: gauge values are material-dependent. “18 ga” in steel ≠ “18 ga” in aluminum or stainless.
Because of that material dependency, professional specifications should always give material + gauge (e.g., “18 ga stainless steel 304”) — or better yet, supply the exact thickness in mm/inches.
2. Standard gauge-to-thickness charts
Below are practical conversion tables used across fabrication shops and procurement documents. Use these as authoritative quick references.
2.1 Common steel gauge chart (mild / carbon steel)
| Gauge | Inches | mm |
|---|---|---|
| 10 ga | 0.1345 in | 3.42 mm |
| 12 ga | 0.1094 in | 2.78 mm |
| 14 ga | 0.0781 in | 1.90 mm |
| 16 ga | 0.0598 in | 1.52 mm |
| 18 ga | 0.0478 in | 1.21 mm |
| 20 ga | 0.0359 in | 0.91 mm |
| 22 ga | 0.0299 in | 0.76 mm |
| 24 ga | 0.0239 in | 0.61 mm |
2.2 Stainless steel (304 / 316 typical) gauge chart
| Gauge | Inches | mm |
|---|---|---|
| 10 ga | 0.1406 in | 3.57 mm |
| 12 ga | 0.105 in | 2.67 mm |
| 14 ga | 0.07874 in | 1.998 mm |
| 16 ga | 0.0625 in | 1.59 mm |
| 18 ga | 0.0508 in | 1.29 mm |
| 20 ga | 0.0359 in | 0.91 mm |
| 22 ga | 0.0299 in | 0.76 mm |
Note: Stainless gauge values are slightly different vs mild steel; always confirm grade.
2.3 Galvanized sheet gauge chart (pre-galvanized/galv)
Galvanized sheet usually follows mild steel thickness with small adjustments for coating.
| Gauge | Inches | mm |
|---|---|---|
| 14 ga | 0.0779 in | 1.98 mm |
| 16 ga | 0.0635 in | 1.61 mm |
| 18 ga | 0.051 in | 1.30 mm |
| 20 ga | 0.038 in | 0.96 mm |
2.4 Aluminum gauge chart (commonly 3000/5000/6000 series)
Aluminum gauges are significantly thinner for the same gauge number.
| Gauge | Inches | mm |
|---|---|---|
| 10 ga | 0.1019 in | 2.59 mm |
| 12 ga | 0.0808 in | 2.05 mm |
| 14 ga | 0.0641 in | 1.63 mm |
| 16 ga | 0.0508 in | 1.29 mm |
| 18 ga | 0.0403 in | 1.02 mm |
| 20 ga | 0.032 in | 0.81 mm |
3. 18 gauge steel — exact thickness, uses and comparisons
You asked about the many 18-gauge queries — here’s the focused explanation.
3.1 What is 18 gauge steel?
18 gauge mild steel thickness ≈ 0.0478 in / 1.21 mm.
18 gauge stainless steel ≈ 0.0508 in / 1.29 mm (depending on standard).
18 gauge aluminum ≈ 0.0403 in / 1.02 mm.
Because of these differences, do not assume “18 ga = one specific mm” without confirming material.
3.2 Typical uses for 18 gauge
HVAC / ductwork: 18 ga galvanized is common for rectangular duct and fittings.
Appliances: body panels, cabinets, and backsplashes.
Automotive trim and interior panels: where moderate strength and formability are needed.
Electrical enclosures: often 18 ga steel or stainless for lighter boxes.
General fabrication: brackets, flanges, small panels.
3.3 18 ga vs 16 ga vs 20 ga — quick comparisons
18 ga vs 16 ga: 16 ga (~1.52 mm) is ~25% thicker; better for load-bearing parts.
18 ga vs 20 ga: 18 ga is thicker; 20 ga (~0.91 mm) is more bendable and cheaper.
18 ga vs 18 ga aluminum: steel is stronger and heavier; aluminum is lighter and corrosion resistant.
4. Quick conversions: gauge → mm → inches
When someone says “18 gauge to mm” use the right table for the material. Here’s a short cheat sheet:
Steel (mild): 18 ga = 1.21 mm = 0.0478 in
Stainless (304): 18 ga ≈ 1.29 mm = 0.0508 in
Aluminum: 18 ga ≈ 1.02 mm = 0.0403 in
Conversion tip: if you must use a single general reference for quick shop conversation, say: “18 ga steel ≈ 1.2 mm.” But always confirm the exact material grade for procurement.
5. Weight per square meter and how to calculate it
Knowing weight is vital for shipping, structural calculations and pricing.
Formula (metric):Weight (kg/m²) = thickness (mm) × density (g/cm³)
Common densities:
Mild steel ~ 7.85 g/cm³
Stainless steel (304) ~ 8.0 g/cm³
Aluminum ~ 2.70 g/cm³
Examples (per m²):
18 ga mild steel (1.21 mm) → 1.21 × 7.85 = 9.50 kg/m²
18 ga stainless (1.29 mm) → 1.29 × 8.0 = 10.32 kg/m²
18 ga aluminum (1.02 mm) → 1.02 × 2.70 = 2.75 kg/m²
Practical: multiply area (m²) × kg/m² to get total weight. For imperial units convert mm→inches and use density in lb/in³ if needed.
6. Common sheet sizes, surface finishes and tolerances
6.1 Standard sheet sizes (examples)
4 × 8 ft (1.219 m × 2.438 m) — common for coils cut to size
5 × 10 ft panels (1.524 m × 3.048 m) — used in heavy industrial sheets
Coil widths: often 600 mm–1250 mm or custom slit widths
6.2 Finishes & coatings
Mill finish (as-rolled/cold-rolled)
Galvanized (G90, etc.) for corrosion protection
Painted / pre-painted (PVDF) for cladding and roofing
Anodized (aluminum) for corrosion & aesthetics
Polished, brushed finishes for stainless panels
6.3 Typical thickness tolerances
+/- 0.02–0.05 mm for cold-rolled stainless; larger tolerances for hot-rolled or coated sheets. Always request tolerance class for precision work.
7. Choosing gauge by application
Below are practical guidelines to match gauge to use — helps engineers and buyers choose the right mix of strength, formability and cost.
7.1 Building & construction
Roofing/Cladding: 24–18 ga galvanized or pre-painted steel depending on exposure.
Interior panels: 22–20 ga steel or aluminum for decorative panels.
Structural enclosures: 16–12 ga for frames and heavy duct supports.
7.2 HVAC & ductwork
Main ducts: 16–18 ga galvanized steel common.
Return/branch ducts: 20–24 ga where airflow and cost matter.
7.3 Automotive
Body panels: 18–20 ga cold-rolled steel or aluminum; design dictates exact gauge.
Chassis & reinforcement: 10–14 ga or thicker, depending on load.
7.4 Appliances & furniture
Cabinet & housings: 18–20 ga stainless or cold-rolled steel.
Shelving: 14–16 ga for heavy racks.
7.5 Precision parts & electrical enclosures
Control panels, boxes: 16–18 ga stainless or mild steel with cutouts and knockouts.
Rule of thumb: choose the thinnest gauge that meets structural and durability requirements — saves cost and weight but maintain safety factor.
8. How to measure sheet metal gauge in the workshop
If you receive a sheet and need to verify thickness:
Caliper or micrometer: measure thickness at several points — best for <3 mm sheets.
Thickness gauge (feeler gauge): less precise but quick.
Digital ultrasonic gauge: for coated or painted panels, measures through coating.
Weigh and calculate: measure area and weight, then compute thickness (reverse of weight formula).
Always average multiple readings, especially if rolling or coating affects apparent thickness.
9. Buying tips — what to ask your supplier (Huaxiao-Alloy checklist)
When you place an order, ask these to avoid surprises:
Material: mild steel / stainless grade (304, 316) / aluminum alloy (5052, 6061) / galvanized spec
Exact thickness in mm/inches (not just gauge)
Gauge standard used (USS, etc.)
Sheet size / slit width & edge type (sheared vs mill)
Tolerance & flatness requirements
Surface finish & coating (galvanized, painted, anodized)
Quantity & coil vs cut sheets
Processing services: slitting, laser-cut, CNC punch, bending — request drawings
Certification: material certificates (MTC / mill test report), inspection requirements
If you want: Huaxiao-Alloy provides certified material with slitting & cut-to-size and can handle sample orders. Contact [email protected] or WhatsApp +1 (579) 300-2733 for a quote.
For mild steel: ~1.21 mm. For aluminum: ~1.02 mm. For stainless it can be ≈1.29 mm. Always specify material.
Yes. Lower gauge numbers are thicker. 18 ga > 20 ga.
14 gauge is thicker than 16 gauge.
1/8 inch ≈ 0.125 in is close to 11–12 gauge depending on material; but it’s better to state exact mm/in.
Prefer mm/inches for procurement. Use gauge for rough conversation or in shops familiar with gauge standards.
Approx 9.5 kg/m² for mild steel (1.21 mm × 7.85 g/cm³).
No. Use the supplier’s chart or quote explicit thickness. European buyers often use mm directly.
Yes — 18 ga is readily formed on press brakes and roll formers. Thinner gauges (20–24) are even more formable.
Many sinks are 18 ga stainless ≈ 1.2–1.3 mm giving a balance of rigidity and cost.
Contact local metal distributors or global suppliers like Huaxiao-Alloy — we supply worldwide and can arrange local logistics.
11. Practical examples: picking the right gauge
Scenario A — Kitchen splashback: stainless steel, visible area, moderate impact: 18 ga (1.2–1.3 mm) gives the right look and stiffness.
Scenario B — Exterior cladding in coastal environment: use 22–24 ga pre-painted galvanized steel for long runs; step up to 20–18 ga in high wind areas.
Scenario C — HVAC rectangular duct main runs: use 16–18 ga galvanized depending on size and internal pressure.
Scenario D — Automotive inner panels: aluminum 18–20 ga for weight saving, with reinforcements in higher gauge where needed.
12. Material & process options Huaxiao-Alloy supplies
| Gauge | Inches | mm |
|---|---|---|
| 10 ga | 0.1345 in | 3.42 mm |
| 12 ga | 0.1094 in | 2.78 mm |
| 14 ga | 0.0781 in | 1.90 mm |
| 16 ga | 0.0598 in | 1.52 mm |
| 18 ga | 0.0478 in | 1.21 mm |
| 20 ga | 0.0359 in | 0.91 mm |
| 22 ga | 0.0299 in | 0.76 mm |
| 24 ga | 0.0239 in | 0.61 mm |
13. Best practices for procurement & quality control
Specify material & thickness (mm) alongside gauge in purchase orders.
Request MTC (mill test certificate) for structural or safety applications.
Order samples for color/finish and thickness verification before mass orders.
Confirm coating weight (for galvanized) and paint system (PVDF vs polyester).
Plan tolerances & nesting for laser cutting to reduce scrap.
Factor shipping weight — thicker gauges add cost quickly.
Conclusion & next steps
A correct understanding of the sheet metal gauge chart saves time, money and reduces rework. Remember:
Gauge is material-dependent — always confirm.
When in doubt, specify thickness in mm or inches, material grade and required finish.
For procurement, use weight calculations to estimate logistics and cost.
If you want accurate sheets, pre-slit coils or precision laser cut parts, Huaxiao-Alloy can help. We supply certified sheet metal in 18 ga and all other gauges, plus processing and global logistics. Contact us:
Email: [email protected]
WhatsApp: +1 (579) 300-2733
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