Resistivity of Metals and Alloys
Resistivity, conductivity, temperature coefficient and percent IACS for 15 metals and alloys.
Resistivity (ρ) is how strongly a material resists electric current, independent of its shape. The resistance of a wire is its resistivity times its length divided by its cross-sectional area. This table lists the resistivity of 15 metals and alloys at 20 C together with the conductivity, the temperature coefficient and the percent IACS, which compares each material with annealed copper.
The table
| Material | Resistivity at 20 C (ohm m) | Conductivity (MS/m) | Temperature coefficient (per K) | Conductivity (percent IACS) |
|---|---|---|---|---|
| Silver | 1.59E-8 | 62.893 | 0.0038 | 62.9 |
| Copper (annealed, IACS) | 1.724E-8 | 58.005 | 0.00393 | 58 |
| Gold | 2.44E-8 | 40.984 | 0.0034 | 41 |
| Aluminum | 2.65E-8 | 37.736 | 0.00429 | 37.7 |
| Zinc | 5.9E-8 | 16.949 | 0.0037 | 16.9 |
| Brass (typical) | 7E-8 | 14.286 | 0.0015 | 14.3 |
| Nickel | 6.99E-8 | 14.306 | 0.006 | 14.3 |
| Iron (pure) | 9.71E-8 | 10.299 | 0.00651 | 10.3 |
| Tin | 1.15E-7 | 8.696 | 0.0042 | 8.7 |
| Steel, carbon (typical) | 1.7E-7 | 5.882 | 0.003 | 5.9 |
| Lead | 2.2E-7 | 4.545 | 0.0039 | 4.5 |
| Titanium | 4.2E-7 | 2.381 | 0.0035 | 2.4 |
| Constantan | 4.9E-7 | 2.041 | 1E-5 | 2 |
| Stainless steel 304 | 7.2E-7 | 1.389 | 0.00094 | 1.4 |
| Nichrome | 1.1E-6 | 0.909 | 0.0004 | 0.9 |
Source and notes: Typical handbook values at 20 C (CRC Handbook). 100 percent IACS = 58.0 MS/m (1.724e-8 ohm m). Alloys vary with composition.
How to use this table
- Find the material in the first column.
- Calculate the resistance of a conductor: R = ρ × L ÷ A (resistivity in ohm meters, length in meters, area in square meters).
- For another temperature, use RT = R20 × (1 + α × (T − 20)) with the temperature coefficient α.
Worked example: 100 m of 2.5 mm² conductor, copper against aluminum
- Copper: R = 1.724E-8 × 100 ÷ 2.5E-6 = 0.690 ohm.
- Aluminum: R = 2.650E-8 × 100 ÷ 2.5E-6 = 1.060 ohm, which is 54 percent more.
- To match the copper resistance, the aluminum conductor needs 3.84 mm² of cross-section, which is why aluminum feeders are one or two sizes larger.
Notes and cautions
- Alloy values vary with composition and treatment; the numbers are typical handbook values.
- Resistivity is not the same as resistance. Resistance depends on the shape of the conductor as well.
Related tools and guides
- Wire Ampacity and Voltage Drop Calculator
- Ohm’s Law and Power Calculator
- AWG Wire Gauge Table
- All reference tables
FAQ
What is IACS?
The International Annealed Copper Standard: a conductivity of 58.0 MS/m (resistivity 1.724E-8 ohm m) defined as 100 percent. Other materials are given as a percentage of it.
What is the resistivity of copper?
About 1.68E-8 to 1.72E-8 ohm m at 20 C, depending on purity and annealing; 1.724E-8 is the IACS reference.
How does temperature change resistance?
Metals get more resistant as they warm. For copper the resistance rises about 0.39 percent for each degree C, so a coil at 80 C has about 24 percent more resistance than at 20 C.
Sources
- CRC Handbook of Chemistry and Physics; IEC 60028 (International standard of resistance for copper).
- Typical handbook values at 20 C (CRC Handbook). 100 percent IACS = 58.0 MS/m (1.724e-8 ohm m). Alloys vary with composition.