An AWG wire resistance chart only produces a usable number when four variables are fixed at the same time: wire size (AWG), conductor material, length, and temperature, with the resistance unit stated explicitly. Resistance tables are normally published in ohms per 1000 feet at a reference temperature (commonly 20°C or 25°C), and copper and aluminum have different resistance values at every gauge. Changing any one of these inputs changes the resistance figure, so a bare “12 AWG resistance” number without the accompanying conditions cannot be compared across projects or verified against a calculator output.
The AWG Wire Resistance Calculator takes conductor size, material, and length as separate fields and returns resistance in ohms, scaled from the per-1000-ft base value. That base value is the fixed physical property of the conductor; the calculator’s arithmetic is the length scaling.
Resistance Per 1000 Feet: 12, 20, and 22 AWG
For solid copper conductors at approximately 20°C, published resistance values are:
| AWG | Resistance (Ω/1000 ft) |
|---|---|
| 12 | ~1.588 |
| 20 | ~10.15 |
| 22 | ~16.14 |
These figures roughly double for aluminum conductors of the same gauge, and they increase as conductor temperature rises above the reference point due to the temperature coefficient of resistance. A chart or calculator that does not specify the reference temperature is only valid near 20–25°C; field-installed conductors operating at higher insulation temperature ratings will show a higher actual resistance than the table value.
Scaling to Actual Conductor Length
The calculator scales the per-1000-ft value linearly:
R (actual) = R (per 1000 ft) × (Length in feet ÷ 1000)
For a two-conductor circuit, the outgoing and return conductors both carry current over the same run length, so total circuit resistance is:
R (circuit) = 2 × R (per conductor)
This doubling applies to any single-phase branch circuit or feeder run where the source and load are connected by a matched pair of conductors — it is not an adjustment factor, it is a count of current-carrying conductors in the resistive path.
Calculation Example
Compare 12 AWG, 20 AWG, and 22 AWG copper conductors at a 50-foot one-way run (100 feet total conductor length for the two-conductor circuit), all at the same temperature:
- 12 AWG: 1.588 Ω/1000 ft × (100/1000) = 0.159 Ω
- 20 AWG: 10.15 Ω/1000 ft × (100/1000) = 1.015 Ω
- 22 AWG: 16.14 Ω/1000 ft × (100/1000) = 1.614 Ω
Holding material, temperature, and length constant isolates gauge as the only variable, which is what the calculator’s side-by-side comparison field is built for. Once the resistance figure is set, feed it into the Voltage Drop Calculator along with circuit current and source voltage to get the actual drop in volts, or into the Wire Size Calculator to check whether a smaller gauge still meets both resistance and ampacity limits for the load.
Review Boundary: Resistance Is Not Ampacity
A resistance value describes only the conductor’s opposition to current flow at a given temperature and length. It does not indicate how much current the conductor is rated to carry. Ampacity is set separately by insulation temperature rating, installation method (raceway, free air, cable tray), ambient temperature correction factors, adjustment factors for the number of current-carrying conductors, terminal ratings, and the overcurrent protective device size. These factors must be confirmed against the applicable code articles adopted by the AHJ before finalizing conductor size — a resistance chart cannot substitute for that check.