Wire Gauge Calculator

Look up wire properties by gauge number or find the right gauge for a given diameter or current. Supports AWG (American Wire Gauge), SWG (Standard Wire Gauge), and metric sizes.

How It Works

What is Wire Gauge?

Wire gauge is a standardized system for measuring the diameter of electrical wire. The most widely used system in North America is the American Wire Gauge (AWG), where smaller gauge numbers indicate larger wire diameters. The British Standard Wire Gauge (SWG) follows a similar principle but uses different diameter values.

AWG Formula

AWG wire diameters follow a geometric progression based on two reference points: AWG 0000 (4/0) = 11.684 mm and AWG 36 = 0.127 mm. The formula for any AWG gauge n is:

Each increase of 6 gauge numbers halves the diameter, and each increase of 3 gauge numbers halves the cross-sectional area (doubling the resistance per unit length).

Key Properties

• Diameter: Physical size of the conductor, determining how it fits in conduits and terminals
• Cross-sectional area: Directly proportional to current-carrying capacity; usually given in mm² or circular mils (cmil)
• Resistance: Determined by material resistivity, length, and cross-sectional area: R = ρL / A
• Ampacity: Maximum current a wire can safely carry, depends on gauge, insulation type, ambient temperature, and installation method

Copper vs. Aluminum

• Copper resistivity: 1.724 × 10⁻⁸ Ω·m at 20°C
• Aluminum resistivity: 2.65 × 10⁻⁸ Ω·m at 20°C (about 1.54× copper)
• Aluminum is lighter and cheaper but requires larger gauge for the same current capacity
• Copper is the standard for most building wiring; aluminum is common in power transmission and large feeders

Voltage Drop

For a two-conductor circuit (hot + neutral or hot + ground return), the voltage drop is:

Where I is the current, R is resistance per unit length, and L is the one-way cable run distance. The NEC recommends a maximum voltage drop of 3% for branch circuits and 5% total for feeder + branch.