MM to Gauge Converter
Convert millimetres to gauge numbers and gauge to millimetres for sheet metal and wire. Supports standard steel, aluminium, galvanized steel, AWG, and SWG standards.
Conversion Result
Conversion Result
Common Gauge to MM Conversions
Sheet metal gauge refers to the thickness of metal sheets, with lower gauge numbers indicating thicker material. Different materials follow different gauge standards, making conversion tables essential for metalworking projects.
Standard Steel Gauge Chart
| Gauge | Millimetres (mm) | Inches | Common Applications |
|---|---|---|---|
| 8 | 4.176 | 0.1644 | Heavy structural components |
| 10 | 3.416 | 0.1345 | Industrial equipment |
| 12 | 2.657 | 0.1046 | Vehicle panels, roofing |
| 14 | 1.897 | 0.0747 | Metal studs, framing |
| 16 | 1.519 | 0.0598 | HVAC ductwork |
| 18 | 1.214 | 0.0478 | Appliances, enclosures |
| 20 | 0.912 | 0.0359 | Light fabrication |
| 22 | 0.759 | 0.0299 | Decorative panels |
| 24 | 0.607 | 0.0239 | Flashing, guttering |
| 26 | 0.455 | 0.0179 | Thin sheet applications |
Aluminium Gauge Chart
| Gauge | Millimetres (mm) | Inches | Common Applications |
|---|---|---|---|
| 8 | 3.264 | 0.1285 | Aircraft components |
| 10 | 2.588 | 0.1019 | Marine fittings |
| 12 | 2.052 | 0.0808 | Trailer construction |
| 14 | 1.628 | 0.0641 | Signage, cladding |
| 16 | 1.290 | 0.0508 | Decorative trim |
| 18 | 1.024 | 0.0403 | Automotive body panels |
| 20 | 0.813 | 0.0320 | Food industry equipment |
| 22 | 0.643 | 0.0253 | Packaging materials |
Wire Gauge Conversions
Wire gauges follow different standards than sheet metal. American Wire Gauge (AWG) is standard in North America, whilst Standard Wire Gauge (SWG) is traditionally used in the UK.
| Gauge | AWG (mm) | SWG (mm) | Typical Wire Applications |
|---|---|---|---|
| 10 | 2.588 | 3.251 | Mains electrical wiring |
| 12 | 2.053 | 2.642 | Household circuits |
| 14 | 1.628 | 2.032 | Light fixtures, outlets |
| 16 | 1.291 | 1.626 | Extension leads |
| 18 | 1.024 | 1.219 | Thermostat wiring |
| 20 | 0.812 | 0.914 | Electronics, low voltage |
| 22 | 0.644 | 0.711 | Computer cables |
| 24 | 0.511 | 0.559 | Telecommunications |
Conversion Formula and Steps
Whilst conversion charts are most practical, gauge thickness can be calculated for standard steel sheets. The Browne & Sharpe formula applies to American standard gauges.
Standard Formula:
Thickness (mm) = 6.073 × 0.8902(gauge – 3)
Example: For 16 gauge steel
Thickness = 6.073 × 0.8902(16-3) = 6.073 × 0.890213 ≈ 1.519 mm
Manual Conversion Steps
To convert MM to Gauge:
- Measure the metal thickness in millimetres with precision callipers
- Identify the material type (steel, aluminium, or galvanized)
- Reference the appropriate gauge chart for that material
- Find the closest matching thickness value
- Note that exact matches are rare; select the nearest gauge
To convert Gauge to MM:
- Identify the gauge number stamped or specified
- Confirm the material standard being referenced
- Locate the gauge in the appropriate conversion table
- Read the corresponding millimetre measurement
Important: Gauge standards vary significantly between materials. 16 gauge steel (1.519 mm) is notably thicker than 16 gauge aluminium (1.290 mm). Always verify which standard applies to your project.
Visual Thickness Comparison
These visual representations show relative thickness differences between common gauge sizes for standard steel.
Material-Specific Gauge Standards
Standard Steel Sheet
The Manufacturers’ Standard Gauge for Sheet Steel represents the most widely adopted standard in the UK and internationally. This system originated in the United States but became the de facto standard for carbon steel sheet products. Thickness decreases as gauge numbers increase, with even-numbered gauges (10, 12, 14, 16, 18, 20) being most commonly stocked.
Aluminium and Non-Ferrous Metals
Aluminium follows the Brown & Sharpe (B&S) gauge system, which produces different thickness values than steel for identical gauge numbers. This distinction is critical in aerospace, automotive, and marine applications where aluminium is preferred for its strength-to-weight ratio. Copper and brass also follow the B&S standard.
Galvanized Steel
Hot-dip galvanized steel sheet includes a zinc coating that adds thickness beyond the base steel. Gauge measurements for galvanized material account for the total thickness including the protective zinc layer. This affects both weight calculations and compatibility with fabrication equipment.
British Standards (SWG)
Standard Wire Gauge (SWG), also known as Imperial Wire Gauge, was established in British Standard 3737. Whilst largely superseded by metric measurements, SWG remains relevant in the UK wire industry, particularly for fencing wire, spring wire, and traditional electrical applications. SWG produces thicker measurements than AWG for the same gauge number.
Industry Applications and Material Selection
Construction and Building
Metal stud framing typically employs 20-25 gauge galvanized steel for non-load-bearing walls, whilst structural applications require 12-16 gauge. Roofing panels generally range from 24-29 gauge, balancing weather resistance with cost. Heavier gauges (18-22) suit high-traffic or impact-prone areas.
Automotive Manufacturing
Modern vehicle bodies utilize varying gauges based on panel location. Structural components and chassis rails require 10-14 gauge steel for strength and crash protection. Outer body panels typically use 18-20 gauge to minimize weight whilst maintaining formability. Aluminium alternatives often specify equivalent gauge numbers despite different actual thickness.
HVAC and Ductwork
Heating, ventilation, and air conditioning systems predominantly use 24-26 gauge galvanized steel for residential ductwork. Commercial installations may specify 20-22 gauge for larger diameter ducts or high-pressure systems. The thinner material reduces cost and weight whilst maintaining adequate structural integrity for internal pressure.
Sheet Metal Fabrication
Job shops and fabricators stock standard gauges in 4-foot by 8-foot or 5-foot by 10-foot sheets. Common workshop inventory includes 16, 18, and 20 gauge steel for general metalwork. Thinner gauges (22-24) suit decorative applications and enclosures, whilst thicker material (10-14 gauge) serves structural projects.
Electrical and Electronics
Equipment enclosures and server racks frequently specify 16-20 gauge steel for electromagnetic shielding and structural support. Aluminium enclosures use comparable gauges adjusted for material density differences. Wire gauge selection affects current-carrying capacity and voltage drop over distance.
Measurement Accuracy and Tolerances
Manufacturing processes introduce slight thickness variations in sheet metal production. Industry standards define acceptable tolerances that vary by gauge and material type.
Standard Tolerances
For steel sheet under 10 gauge, typical tolerance is ±0.15 mm. Material from 10-20 gauge allows ±0.10 mm variation. Thinner gauges (20+) specify ±0.075 mm tolerance. Aluminium products generally hold tighter tolerances due to different production methods. Precision applications may require verified thickness testing.
Measuring Metal Thickness
Digital callipers provide accurate thickness readings to 0.01 mm precision. Measure at multiple points across the sheet, as rolling processes can create minor variations. Coatings, paint, or oxidation add thickness; clean surfaces before measurement for base metal readings. Micrometer gauges offer higher precision for quality control applications.
Frequently Asked Questions
Why do different materials have different gauge thicknesses?
Gauge standards developed independently for different materials throughout industrial history. Steel gauge systems originated from rolling mill capabilities, whilst wire gauges evolved from drawing die standards. These separate origins created distinct measurement systems that persist in modern manufacturing despite metric standardization efforts.
Is a higher gauge number thicker or thinner?
Higher gauge numbers indicate thinner material across all standard gauge systems. This inverse relationship originates from historical manufacturing processes where gauge number represented the number of passes through rolling mills. More passes produced thinner sheet, resulting in higher gauge numbers for reduced thickness.
Can I substitute one gauge for another in a project?
Substitution depends on application requirements. Structural components require specified gauges to meet load ratings and building codes. Decorative or non-critical applications allow more flexibility. When substituting, consider material strength, weight implications, fastening methods, and local regulations. Thicker gauges increase cost but improve durability.
How does galvanizing affect gauge measurements?
Galvanized steel gauge measurements include the zinc coating thickness. A 20 gauge galvanized sheet is thicker than 20 gauge uncoated steel due to the protective layer. The zinc coating typically adds 0.05-0.15 mm depending on coating class (G60, G90, etc.). This affects material weight, bending operations, and hole punching.
What’s the difference between AWG and SWG for wire?
American Wire Gauge (AWG) and Standard Wire Gauge (SWG) use different mathematical progressions. For identical gauge numbers, SWG wire measures thicker than AWG. SWG 16 equals approximately 1.63 mm diameter, whilst AWG 16 measures about 1.29 mm. This difference matters significantly in electrical applications where conductor size affects amperage capacity.
Why aren’t gauge measurements in metric units?
Gauge systems predate widespread metric adoption in English-speaking countries. Despite metric conversion efforts, gauges persist due to established industry infrastructure, tooling investments, and standard sheet sizes. Many manufacturers now list both gauge numbers and metric equivalents. Fully metric thickness specifications (like “1.5 mm sheet”) are increasingly common in European markets.
How do I choose the right gauge for sheet metal bending?
Thinner gauges (20-24) bend more easily with lighter equipment but may spring back or wrinkle. Heavier gauges (10-16) require press brakes with higher tonnage and produce stronger bent parts. Material formability also depends on alloy composition and temper. For tight radius bends, specify thinner material or consider material with improved ductility.
Do stainless steel and mild steel share the same gauge chart?
Yes, stainless steel and mild (carbon) steel follow the same Manufacturers’ Standard Gauge. However, stainless steel’s higher strength means thinner gauges can sometimes substitute for thicker mild steel in structural applications. Stainless costs significantly more, so gauge selection affects project economics. Different stainless grades (304, 316, etc.) have identical gauge thickness values.