What ampacity values are used?

Values are based on NEC Table 310.16 for conductors rated at 60°C and 75°C in a conduit at 30°C ambient. Real-world ampacity may differ based on conduit fill, ambient temperature, and insulation type — always consult the NEC or a licensed electrician for code-compliant designs.

What resistivity values are used for resistance calculations?

Copper: 1.724 × 10⁻⁸ Ω·m (0.01724 Ω·mm²/m) at 20°C. Aluminum: 2.825 × 10⁻⁸ Ω·m (0.02825 Ω·mm²/m) at 20°C. These are standard values for annealed copper and electrical-grade aluminum. Resistance increases roughly 0.4% per °C above 20°C.

Why does AWG go up as wire gets thinner?

AWG (American Wire Gauge) is a logarithmic scale derived from wire-drawing steps. Each increase of 6 AWG numbers halves the cross-sectional area (and roughly halves the ampacity). So AWG 4 is thicker and can carry more current than AWG 10.

How is resistance per 1000 ft calculated?

R = (ρ × L) / A, where ρ is resistivity in Ω·mm²/m, L is 304.8 m (1000 ft), and A is the conductor area in mm². This gives the single-conductor resistance for 1000 ft of wire — for round-trip resistance, double this value.

Does this tool account for temperature derating?

The ampacity values shown are for 30°C ambient. If your installation has higher ambient temperature, bundled conductors, or more than 3 current-carrying conductors in a conduit, you must apply NEC correction factors, which can reduce ampacity significantly.

When should I use aluminum instead of copper wire?

Aluminum wire is lighter and less expensive per foot, making it common for large feeders, service entrances, and utility runs. However, aluminum has about 61% the conductivity of copper, so you need a larger AWG size for the same ampacity. Aluminum also requires special terminations rated for aluminum conductors.

Wire Gauge Calculator

Select an AWG gauge, conductor material, and wire length to instantly calculate current-carrying capacity and total resistance.

Wire Parameters

Conductor Material

Wire Gauge (AWG)

Wire Length (feet, one-way)

Length Unit

Load Current (A) optional — for adequacy check

Result

Select a gauge and press Calculate

AWG Quick Reference

Gauge	Diameter (in)	Area (mm²)	Cu Amp (60°C)	Cu Amp (75°C)	Al Amp (75°C)

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Summary

This calculator provides the current-carrying capacity (ampacity) and resistance for American Wire Gauge (AWG) conductors made of copper or aluminum. Ampacity values are based on NEC Table 310.16 for 60°C and 75°C insulation ratings at 30°C ambient. Resistance is calculated using the standard formula R = ρ × L / A, where ρ is the material resistivity, L is the conductor length, and A is the cross-sectional area. Results help engineers and electricians select the correct wire size for safe, code-compliant installations.

How it works

Select the conductor material: copper or aluminum.
Choose an AWG wire gauge from the dropdown list.
Enter the total one-way wire length in feet or meters.
Click Calculate to see ampacity, resistance, and wire properties.
Review the ampacity ratings and compare against your load current.
Use the recommendation badge to quickly confirm whether the selected gauge is adequate.

Use cases

Select the correct wire gauge for residential branch circuits.
Verify ampacity before running a long feeder to a subpanel.
Calculate total wire resistance for DC solar or battery systems.
Check if an existing wire can handle an increased load safely.
Look up AWG properties (diameter, area, resistance) at a glance.
Compare copper vs. aluminum ampacity to choose the right conductor.
Design low-voltage wiring where resistance and voltage drop matter.
Quickly reference NEC 60°C and 75°C ampacity values for inspections.

Frequently Asked Questions

Last updated: 2026-05-23 · Reviewed by Nham Vu