AWG conductor resistance

DC resistance of solid copper by gauge, with the geometry it is derived from and the temperature correction that is usually left out.

Resistance by gauge at 20 °C

Gauge	Diameter (mm)	Area (mm²)	Ω / 100 m	Ω / 1000 ft	Typical use
22 AWG	0.6438	0.3255	5.29	16.12	Thicker horizontal cable, long PoE runs
23 AWG	0.5733	0.2582	6.68	20.36	Cat 6 / Cat 6A horizontal
24 AWG	0.5106	0.2047	8.42	25.66	Cat 5e / Cat 6 horizontal, most common
26 AWG	0.4049	0.1288	13.39	40.81	Patch cords, stranded
28 AWG	0.3211	0.0810	21.29	64.89	Slim patch cords, high-density panels

How these are derived

Diameter follows the AWG definition, where each three gauge numbers roughly halve the area:

d = 0.127 mm × 92^{(36 − n) / 39}

Resistance then follows from resistivity and geometry, with ρ = 1.724×10⁻⁸ Ω·m for annealed copper at 20 °C:

R = ρ · L / A

Temperature correction

Copper resistance rises about 0.393 % per °C. This is the correction people most often skip, and it is worth 16 % between a bench measurement and a cable in a hot ceiling void.

R(T) = R₂₀ · [ 1 + 0.00393 · (T − 20) ]

Temperature	22 AWG	23 AWG	24 AWG	26 AWG	28 AWG
0 °C	4.87	6.15	7.76	12.34	19.62
20 °C	5.29	6.68	8.42	13.39	21.29
40 °C	5.71	7.21	9.08	14.44	22.96
60 °C	6.12	7.73	9.74	15.49	24.64
80 °C	6.54	8.26	10.41	16.55	26.31

All values in Ω per 100 m per conductor.

Solid and stranded

Stranded conductors present roughly 1.05× the resistance of solid for the same nominal gauge, because the individual strands take a helical path and the effective copper area is lower. Patch cords are stranded; horizontal cable is solid.

Nominal versus specification limit

The figures above are nominal copper. Cabling standards permit worse: the TIA limit for a 24 AWG horizontal conductor is 9.38 Ω/100 m against the 8.42 Ω nominal, around 11 % higher. Design against the limit when you do not know what cable you are getting.

Related tool: PoE voltage drop and power budget, which uses these figures with the loop geometry of 802.3af, 802.3at and 802.3bt.