A wire gauge calculator converts between American Wire Gauge (AWG) and metric (mm²) wire sizes, showing ampacity ratings, resistance values, and voltage drop. Whether you are wiring a home circuit, sizing cable for solar panels, or selecting wire for an industrial installation, this tool gives you all the specifications you need in one place.
Wire Gauge Converter
Voltage Drop Calculator (Optional)
AWG Reference Table
| AWG | mm² | Diameter (mm) | Copper (A) | Aluminum (A) | Ω/1000ft |
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How to Use the Wire Gauge Calculator
Selecting the correct wire gauge is critical for electrical safety and efficiency. Wire that is too thin for the current it carries can overheat, cause voltage drop at the load, and even start fires. This free wire gauge calculator helps you convert between AWG and metric mm² sizes, check ampacity ratings, and calculate voltage drop for any installation.
Step 1: Choose Your Conversion Mode
Select either "AWG to mm²" or "mm² to AWG" depending on which unit you are starting with. AWG (American Wire Gauge) is the standard in North America, while mm² (square millimeters) is used in most other countries and in IEC standards. The converter handles both directions instantly.
Step 2: Enter Your Wire Size
For AWG mode, select a gauge from the dropdown ranging from 4/0 (the thickest) down to 20 (very thin). For mm² mode, type in any cross-sectional area value. The calculator determines the closest AWG equivalent and shows the exact conversion including diameter in both millimeters and inches.
Step 3: Review Ampacity and Resistance
After converting, the results show the ampacity rating for both copper and aluminum conductors based on NEC (National Electrical Code) standards for 60°C insulation. Resistance values are shown per 1000 feet and per kilometer, which you need for voltage drop calculations and circuit design.
Step 4: Calculate Voltage Drop (Optional)
For longer wire runs, voltage drop becomes a concern. Enter your system voltage, current draw, one-way cable distance, and conductor material. The voltage drop calculator uses the wire's resistance to determine the total drop, percentage, end voltage at the load, and power wasted as heat in the wire. The NEC recommends keeping voltage drop under 3% for branch circuits and 5% for the total from service to load.
Understanding the Reference Table
The full reference table at the bottom covers AWG sizes from 4/0 through 20. It shows the cross-sectional area in mm², diameter in millimeters, ampacity for both copper and aluminum conductors, and resistance per 1000 feet. Use this table to quickly compare wire sizes and find the right gauge for your application without converting each one individually.
When to Size Up
Always consider going one gauge thicker than the minimum if: the wire will be installed in conduit with other conductors (which reduces ampacity due to heat), the ambient temperature exceeds 30°C (86°F), or the run is in a location where replacement would be difficult. A slightly larger wire costs more upfront but provides a safety margin and reduces energy losses over the life of the installation.
FAQ
Is this wire gauge calculator free to use?
Yes, this wire gauge calculator is completely free with no limits. Convert between AWG and mm² as many times as you need without signing up or paying anything.
Is my data safe when using this tool?
Absolutely. All calculations run entirely in your browser using JavaScript. No data is ever sent to a server. The tool works completely offline once the page loads.
What is AWG and how does it work?
AWG stands for American Wire Gauge, a standardized system for measuring wire diameter. The numbering is counterintuitive: smaller numbers mean thicker wire. AWG 4/0 (0000) is the thickest common size at 107.2 mm², while AWG 20 is thin at just 0.518 mm².
How do I convert AWG to mm²?
Select 'AWG to mm²' mode and choose or enter your AWG number. The calculator uses the standard formula: diameter (mm) = 0.127 × 92^((36-AWG)/39), then converts to cross-sectional area. Results include diameter in both mm and inches.
What is ampacity and why does it matter?
Ampacity is the maximum current a wire can safely carry without overheating. Exceeding a wire's ampacity rating creates a fire hazard. This calculator shows ampacity ratings for both copper and aluminum conductors based on NEC standards.
How do I calculate voltage drop?
Enter your system voltage, current draw in amps, one-way wire distance in feet, and conductor material. The calculator determines the voltage drop using wire resistance data. Keep voltage drop under 3% for branch circuits and 5% for total feeders per NEC recommendations.
What is the difference between copper and aluminum wire?
Copper has lower resistance and higher ampacity per gauge than aluminum, but costs significantly more. Aluminum wire is lighter and cheaper, making it common for utility feeds and large branch circuits. Aluminum requires larger gauges to carry the same current as copper.
Which wire gauge do I need for a 20-amp circuit?
For a 20-amp copper circuit, you need at least 12 AWG wire per NEC code. For aluminum, you need 10 AWG. Always check local electrical codes as requirements may vary, and consider voltage drop for longer runs.