SWG to mm Calculator

Convert Standard Wire Gauge (SWG / British Wire Gauge) to millimeters and inches.

Conversion

SWG Gauge Standard Wire Gauge (British Imperial Standard)

SWG Standard

SWG uses fixed lookup table values

Unlike AWG, SWG (Standard Wire Gauge) does not follow a mathematical formula — each gauge number maps to a fixed diameter defined by British Standard BS 3737. This calculator uses the official BS 3737 values.

Diameter

— mm

Conversion Details

FULL SPECIFICATION

ParameterValue

Cross-Section Area—

About SWG to mm Conversion

SWG (Standard Wire Gauge), also known as British Wire Gauge, is used in the UK and many Commonwealth countries for wires, sheet metal, and tubing. All diameters come from the official BS 3737 standard lookup table. SWG runs from 7/0 (thickest, 12.7 mm) to 50 (thinnest, 0.025 mm).

ℹ️ About SWG to mm Calculator

Convert Standard Wire Gauge (SWG — used in UK) to millimeters. Essential when working between UK and international wiring specifications.

📋 How to Use

Enter the required values (AWG, current, length, voltage).
Select the wire material (copper or aluminum) if applicable.
Click Calculate.
Use the result to select the correct wire for your application.

🔢 Formula / Calculation Method

SWG tables define exact diameters for each gauge number

SWG 12 = 2.642mm | SWG 16 = 1.626mm

👥 Who Uses It

Electricians sizing residential and commercial wiring
Solar installers designing PV systems
Contractors planning electrical runs
DIY homeowners doing safe wiring projects
Engineers designing power distribution

📌 Practical Examples

Home Circuit

20A kitchen circuit → use AWG 12 copper.

Solar Run

Long solar panel run → calculate voltage drop first.

EV Charger

Level 2 EV charger (40A) → AWG 8 copper minimum.

Sub-Panel

100A sub-panel → AWG 3 or 2 copper feeder.

⭐ Benefits

🔌

Safe Wiring

Correct gauge prevents fire risk

⚡

Voltage Drop

Ensure proper voltage delivery

📏

Exact Size

mm and AWG conversions

📱

Mobile

Use on job site

🆓

Free

No cost or login

🎯

Accurate

NEC-aligned calculations

💡 Tips

💡Always use the next lower AWG (thicker wire) when in doubt — oversize is always safer.
💡Aluminum wire requires larger gauge than copper for the same current.
💡Keep voltage drop under 3% (NEC recommendation) for efficiency.
💡For outdoor or direct burial, use wire rated for that environment.

❓ Frequently Asked Questions

What AWG do I need for 20 amps?

Use AWG 12 for a 20-amp circuit (copper).

What is voltage drop and why does it matter?

Voltage drop is the loss of voltage over a wire run. Over 3% drop causes equipment inefficiency.

Copper vs aluminum wire?

Copper is preferred — aluminum requires 1–2 gauges larger for the same ampacity.

Is the calculator NEC compliant?

Results are based on NEC ampacity tables — always verify with a licensed electrician.

Is it free?

Yes, completely free.

🔗 Related Calculators

🚀 Features

⚡

Instant Results

Calculate in seconds, no waiting

🎯

High Accuracy

Precise results every time

📱

Mobile Friendly

Works on any device or screen size

🔒

Privacy First

No data stored or shared

🌍

Works Worldwide

Available 24/7 from anywhere

🆓

100% Free

Always free, no registration needed

⚠️ Common Mistakes to Avoid

⚠️Using too-thin wire — always verify ampacity before installation.
⚠️Ignoring voltage drop on long wire runs.
⚠️Forgetting derating factors for bundled wires or high temperatures.
⚠️Using indoor-rated wire in outdoor or wet locations.

📖 Glossary

AWG

American Wire Gauge — lower number = thicker wire.

Ampacity

Maximum current a wire can safely carry.

Voltage Drop

Reduction in voltage along a wire due to resistance.

SWG

Standard Wire Gauge — British standard for wire sizes.

NEC

National Electrical Code — US standard for safe electrical installations.

Derating

Reducing wire ampacity for bundled or high-temperature conditions.

📢 Disclaimer

Wire gauge calculations are for reference only. All electrical wiring must comply with local building codes and be performed or verified by a licensed electrician.