PCB Trace Resistance Calculator
The DC resistance of a printed circuit board copper trace is set by its dimensions and the resistivity of copper. A longer or narrower trace, or thinner copper, raises resistance, increasing voltage drop and resistive heating. This calculator uses the textbook conductor formula R equals resistivity times length divided by cross-sectional area, with a temperature correction term. Enter the trace length, width, copper thickness, operating temperature, and copper resistivity to find the trace resistance, its cross-sectional area, and the power dissipated at a given current.
PCB trace resistance formula
Area A = width * thickness (in square metres)
rho(T) = rho25 * [1 + alpha * (T - 25)]
Resistance R = rho(T) * length / A
Voltage drop V = R * current
Power P = current^2 * R
Lengths are entered in millimetres and converted to metres internally. The cross-sectional area equals width times copper thickness. The resistivity is temperature-corrected with copper's temperature coefficient before computing resistance.
Copper trace facts
- Annealed copper resistivity is about 1.68e-8 ohm-metres near room temperature.
- Copper's temperature coefficient of resistance is roughly 0.00393 per degree Celsius near 25 C.
- 1 oz copper foil is about 0.035 mm thick; 2 oz is about 0.070 mm.
- Halving trace width doubles resistance for the same length and thickness.
- This computes DC resistance only; skin effect raises AC resistance at high frequency.
PCB trace resistance: frequently asked questions
How is PCB trace resistance calculated?
Trace resistance follows the standard conductor formula R = rho * L / A, where rho is the resistivity of copper, L is the trace length, and A is the cross-sectional area (width times thickness). A temperature correction term, 1 + alpha * (T - 25), adjusts resistivity for operating temperature using copper's temperature coefficient of resistance.
What resistivity value should I use for copper?
The widely accepted resistivity of annealed copper at 20 to 25 degrees Celsius is about 1.68e-8 ohm-metres (1.68 micro-ohm-cm). This is a physical material property. The calculator exposes it as an editable input so you can substitute a value matched to your specific copper foil or supplier datasheet.
How do I convert copper weight in ounces to thickness?
Copper foil weight in ounces per square foot maps directly to thickness: 1 oz copper is about 35 microns (0.035 mm), 2 oz is about 70 microns, and 0.5 oz is about 17.5 microns. Enter the thickness in millimetres in this calculator. Use your fabricator's finished-copper specification for accuracy.
Why does temperature increase trace resistance?
Copper's resistivity rises with temperature. The temperature coefficient alpha is approximately 0.00393 per degree Celsius near room temperature. A trace running at 85 degrees Celsius has roughly 24 percent higher resistance than at 25 degrees Celsius, which raises voltage drop and self-heating.
Does this account for skin effect at high frequency?
No. This calculator computes DC resistance. At high frequencies, current crowds toward the conductor surface (skin effect), raising the effective AC resistance above the DC value. For RF traces, use a skin-depth calculation in addition to this DC figure.
Official sources
- NIST: Fundamental physical constants and material properties.
- IPC: IPC-2152 standard for current capacity of conductors.
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.