Wire Gauge Calculator

Wire gauge is a measurement system that runs backwards from intuition: higher numbers mean thinner wire, and lower numbers mean thicker wire. A 12-gauge wire is significantly thicker than a 22-gauge wire. This counterintuitive numbering, combined with the existence of multiple competing gauge systems, creates genuine confusion for electricians, hobbyists, and engineers who need to specify wire size correctly for safety and performance.

Steel Wire Gauge (SWG)

The British Standard Wire Gauge (SWG) is used for steel wire, some electrical applications in the UK, and various industrial applications. SWG and AWG have the same counterintuitive direction (higher number = thinner) but different numerical values for the same physical diameter.

AWG 10 = 2.588 mm diameter. SWG 10 = 3.251 mm diameter. These are noticeably different — a 25.6% diameter difference. Using SWG tables when you need AWG (or vice versa) will produce wrong wire selection. Always verify which gauge system is being used before sourcing wire for a specific application.

Common SWG applications: guitar strings (typically 9 to 13 for electric, 10 to 47 for acoustic), fishing line (some specifications), and certain UK industrial specifications. Guitar string gauges use their own terminology entirely: "light" = .009-.042, "medium" = .013-.056, etc., where the number is the string diameter in thousandths of an inch. These overlap with other gauge systems only coincidentally and shouldn't be confused with them.

Gauge Systems for Non-Electrical Wire

Shotgun gauge is measured by how many lead balls of bore diameter make up one pound. A 12-gauge shotgun has a bore where 12 lead balls of that diameter weigh 1 pound. Smaller gauge numbers = larger bore. 10-gauge is larger bore than 12-gauge, which is larger than 20-gauge. The system is historic and unrelated to wire gauge systems.

Sheet metal gauge (for steel) is yet another separate system. 16-gauge steel sheet is 0.0598 inches (1.519 mm) thick. 18-gauge is 0.0478 inches (1.214 mm). 20-gauge is 0.0359 inches (0.912 mm). Again, higher number = thinner. But the numerical values are entirely different from AWG, SWG, or any other wire gauge system. Always confirm which gauge system applies to the specific material and application being specified.

Related Calculators

• Length & Distance Converter
• Unit Converter
• Energy Unit Converter

The American Wire Gauge System

The American Wire Gauge (AWG) system, also called the Brown & Sharpe gauge, is the standard for electrical wire in the United States. AWG numbers run from 0000 (4/0, the thickest at 11.68 mm diameter) through 40 (the thinnest at 0.0799 mm diameter). Each step change in AWG represents a specific ratio: three AWG steps doubles or halves the cross-sectional area, and six AWG steps doubles or halves the diameter.

Common AWG sizes and their applications: 14 AWG (1.63 mm diameter) is the minimum for household lighting circuits; 12 AWG (2.05 mm) is standard for 20-amp kitchen circuits; 10 AWG (2.59 mm) for clothes dryers and larger appliances; 8 AWG (3.26 mm) and 6 AWG (4.11 mm) for 240V circuits; 2 AWG (6.54 mm) for service panel connections; 1/0 AWG (8.25 mm) for main service entrance conductors.

Ampacity — the current-carrying capacity before overheating — increases with wire size (decreasing AWG number). The NEC (National Electrical Code) specifies ampacity ratings: 14 AWG carries 15 amps, 12 AWG carries 20 amps, 10 AWG carries 30 amps, 8 AWG carries 40-50 amps, 6 AWG carries 55 amps. Using undersized wire for a given current load is a fire hazard. This is why electrical codes mandate minimum wire gauges for specific applications.

Practical Wire Selection Guide

For home electrical work (always check local codes and hire a licensed electrician for permitted work): 15-amp circuits use 14 AWG minimum, 20-amp circuits use 12 AWG minimum, 30-amp circuits use 10 AWG minimum, 40-amp circuits use 8 AWG minimum, 50-amp circuits use 6 AWG minimum. These are code minimums — upsizing is generally acceptable and sometimes wise for long runs.

For automotive wiring: 18 AWG for signal and lighting under 7 amps, 16 AWG for lighting 7-12 amps, 14 AWG for accessories 12-20 amps, 12 AWG for accessories 20-30 amps, 10 AWG for major accessories 30-45 amps, 8 AWG for primary circuits up to 60 amps. Automotive fusing should always protect wire from exceeding its ampacity.

For speaker wire in audio systems: 18 AWG for runs under 24 feet at 4-ohm loads, 16 AWG for runs up to 50 feet, 14 AWG for runs up to 75 feet, 12 AWG for long runs over 75 feet. Thicker speaker wire reduces resistance and preserves audio quality over long runs, though the audible difference is typically minimal beyond what the math suggests for moderate distances.

Metric Wire Gauges and International Standards

Most of the world uses the metric system for wire specifications, measured directly in millimeters (mm) diameter or square millimeters (mm²) cross-sectional area. Converting between AWG and metric: AWG 12 = 2.05 mm = 3.31 mm². AWG 10 = 2.59 mm = 5.26 mm². AWG 8 = 3.26 mm = 8.37 mm².

European wiring standards (IEC 60228) specify wire by cross-sectional area in mm². Common European wire sizes: 1.5 mm² (comparable to 14-15 AWG), 2.5 mm² (comparable to 12-13 AWG), 4 mm² (comparable to 11-12 AWG), 6 mm² (comparable to 10 AWG), 10 mm² (comparable to 7-8 AWG). For electrical work following European drawings or specifications, these conversions matter for selecting equivalent AWG wire in US hardware stores.

Japanese wire specifications use both a JIS (Japanese Industrial Standard) gauge and mm² area measurements. Japanese household wiring is typically 1.6 mm or 2.0 mm diameter single conductors (not specified by a gauge number), which correspond approximately to AWG 14 and AWG 12 respectively.

Resistance, Voltage Drop, and Wire Selection

Wire gauge directly determines electrical resistance per unit length, which determines voltage drop over long wire runs. Resistance increases as wire gets thinner (higher AWG number). AWG 12 copper wire has resistance of 5.21 ohms per 1,000 feet. AWG 14 = 8.28 ohms per 1,000 feet. AWG 16 = 13.17 ohms per 1,000 feet.

Voltage drop becomes significant in long wire runs. A 120V circuit supplying lights 150 feet from the panel (300 feet total circuit length) using 14 AWG: resistance = 300 ÷ 1,000 × 8.28 = 2.484 ohms. At 12 amps: voltage drop = 12 × 2.484 = 29.8 volts. That's 24.8% voltage drop — resulting in only 90V at the fixtures. The NEC recommends no more than 3% voltage drop on branch circuits. This calculation demands upsizing to 10 AWG for long runs, even though 14 AWG handles the amperage safely in terms of heat.

For solar and DC systems, voltage drop calculations are critical because lower voltages (12V, 24V, 48V) have proportionally larger percentage drops from the same absolute voltage loss. A 2V drop on a 12V system is 16.7% — catastrophic for battery charging efficiency. On a 120V AC system, 2V is only 1.7% — acceptable. DC systems need significantly heavier wire gauges than equivalent AC systems for the same current over the same distance.