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Electrical Resistivity of Copper at 20 °C

ρCu=1.7241×10−8 Ω⋅m\rho_{\mathrm{Cu}} = 1.7241 \times 10^{-8}\ \Omega{\cdot}\text{m}
Value17.241 nΩ·m (1.7241 × 10⁻⁸ Ω·m)
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StatusMeasured: ± 0.05 nΩ·m (0.29 % relative)
SourceNBS Handbook 100, Copper Wire Tables (1966): 100 % IACS is 1.7241 µΩ·cm at 20 °C (0.017241 Ω·mm²/m, 10.371 Ω·cmil/ft)
CategoriesMaterial PropertiesEngineering & Trade
Electrical Resistivity of Copper at 20 °C in every electrical resistivity unit
UnitValue
nanoohm meter17.241 nΩ·m
ohm centimeter0.0000017241 Ω·cm
ohm meter1.7241000e-08 Ω·m
ohm circular mil per foot10.370987 Ω·cmil/ft
microohm centimeter1.7241 μΩ·cm
microohm meter0.017241 μΩ·m
ohm square millimeter per meter0.017241 Ω·mm²/m
milliohm centimeter0.0017241 mΩ·cm
kiloohm centimeter1.7241000e-09 kΩ·cm
megaohm centimeter1.7241000e-12 MΩ·cm

Learning zone

The International Annealed Copper Standard, set in 1913 as the 100 % IACS reference for commercial conductor, is 1.7241 × 10⁻⁸ Ω·m at 20 °C, which is 1/58 Ω·mm²/m or 10.371 Ω·cmil/ft, and the NBS copper wire tables are built on it. Laboratory-pure copper measures a few percent lower, and modern high-conductivity copper exceeds 100 % IACS. Voltage-drop constants such as K = 12.9 Ω·cmil/ft start from the IACS figure and add allowances for operating temperature and stranding.

The 20 °C qualifier is not decoration. Copper's resistance rises about 0.393 % per kelvin, so a conductor at its 75 °C insulation rating has 22 % more resistance than the table value: 22 % more voltage drop and 22 % more I²R heat than a cold-copper calculation predicts. That is why motor winding temperature is measured by resistance change, and why voltage-drop calculations on heavily loaded feeders should use the hot resistance. Alloying is brutal in the other direction: brass is four times as resistive as copper, and that is why terminals matter.

Used by 4 solvers

Conductor Resistance Temperature Correction

R2=R1[1+α(T2−T1)]R_{2} = R_{1} \left[ 1 + \alpha (T_{2} - T_{1}) \right]

Resistance of a Wire (R = ρL/A)

R=ρLAR = \frac{\rho L}{A}

Voltage Drop, Single Phase

Vd=2ρLIAV_{d} = \frac{2 \rho L I}{A}

Voltage Drop, Three Phase

Vd=3 ρLIAV_{d} = \frac{\sqrt{3} \, \rho L I}{A}
Revised 8 November 2026
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formula.expert. (2026, November 8). Electrical Resistivity of Copper at 20 °C. https://formula.expert/constants/resistivity-copper-20c