Trace Resistance

Formula

Description

Trace resistance follows the standard resistance formula with copper resistivity (1.724 × 10⁻⁶ Ω·cm at 20°C). Even though copper is an excellent conductor, long and thin traces can have non-trivial resistance. For 1 oz copper (35μm thick), a 10 mil wide trace has about 0.5Ω per inch (roughly 0.2Ω per cm). This resistance causes voltage drops and power losses that matter for power delivery, current sensing, and low-voltage circuits. The sheet resistance of 1 oz copper is approximately 0.5 mΩ/square.

Variables

• R — Trace resistance (Ω)
• ρ — Copper resistivity (1.724 × 10⁻⁶ Ω·cm)
• L — Trace length (cm)
• A — Cross-sectional area (cm²)

Practical Notes

Copper resistivity increases with temperature: approximately +0.39% per °C. At 100°C, resistivity is about 30% higher than at 20°C. For precision current sense traces, use copper pour with defined geometry and account for the temperature coefficient. Plated vias also add resistance: a typical via adds 0.5-3 mΩ.