PCB Trace Resistance
Calculate PCB trace resistance from width, length, and copper thickness using the resistivity formula with temperature correction for electronics design.
About This Calculator
The PCB Trace Resistance Calculator computes the DC resistance of a copper trace on a printed circuit board based on its physical dimensions and operating temperature. This tool is essential for PCB designers, electronics engineers, and hobbyists who need to verify that their trace geometries meet voltage drop and power dissipation requirements before manufacturing.
The calculator uses the standard resistivity formula: R = ρ × L / (W × T) × (1 + α(Tamb − 20°C)), where ρ is copper resistivity (1.724 × 10⁻⁸ Ω·m), L is trace length, W is trace width, T is trace thickness converted from copper weight (1 oz/ft² = 35 μm), and α is copper's temperature coefficient (0.00393 /°C). The optional current input extends the calculator to compute voltage drop (V = I × R) and power dissipation (P = I² × R) — key parameters for power delivery design.
Regional Notes
PCB trace resistance calculations use the same physics worldwide. Copper resistivity and temperature coefficient are material constants independent of region. PCB copper weight is specified in oz/ft² globally (per IPC-2221A standard). Metric dimensions (mm) are used for consistency, though trace widths are often specified in mils in North America (1 mil = 0.0254 mm).
Frequently Asked Questions
What is PCB trace resistance and why does it matter?
PCB trace resistance is the electrical resistance of the copper trace on a printed circuit board. It matters because high trace resistance causes voltage drops, power loss as heat, and signal degradation. For power delivery traces and high-frequency signals, keeping resistance low is critical for reliable circuit operation.
How is PCB trace resistance calculated?
PCB trace resistance is calculated using the formula R = ρ × L / (W × T) × (1 + α(T_amb - 20°C)), where ρ is the resistivity of copper (1.724 × 10⁻⁸ Ω·m at 20°C), L is trace length, W is trace width, T is trace thickness, α is the temperature coefficient of copper (0.00393 /°C), and T_amb is the ambient temperature.
What factors affect PCB trace resistance?
Four main factors affect PCB trace resistance: trace length (longer = higher resistance), trace width (narrower = higher resistance), copper thickness (thinner = higher resistance), and temperature (higher temperature increases resistance due to copper positive temperature coefficient). PCB designers adjust these parameters to meet resistance and voltage drop targets.
How do I convert copper weight (oz/ft²) to thickness?
Standard PCB copper weight converts to thickness as follows: 0.5 oz/ft² = 17.5 μm, 1 oz/ft² = 35 μm, 2 oz/ft² = 70 μm, 3 oz/ft² = 105 μm. The formula is thickness (mm) = copper weight (oz/ft²) × 0.0348. Most PCBs use 1 oz/ft² copper for standard designs and 2 oz/ft² for higher current applications.
What is a typical PCB trace resistance value?
A typical 1 oz copper trace that is 1 mm wide and 100 mm long has a resistance of approximately 50 mΩ at 25°C. Short, wide traces on thick copper can have resistances below 1 mΩ, while long, narrow traces on thin copper can exceed several ohms. The calculator provides results with six decimal places for precision.
How does temperature affect PCB trace resistance?
Copper has a positive temperature coefficient of 0.00393 /°C, meaning resistance increases by about 0.4% for every 1°C rise in temperature. A trace that measures 50 mΩ at 25°C will measure about 54 mΩ at 45°C. This thermal effect is important for power electronics and high-temperature environments.
How do I calculate voltage drop across a PCB trace?
Voltage drop across a PCB trace is calculated using Ohm's Law: V_drop = I × R, where I is the current through the trace and R is the trace resistance. Enter the expected current in the optional current field, and the calculator will compute both voltage drop and power dissipation (I²R) automatically.
What copper weight should I use for my PCB?
Standard PCB copper weight is 1 oz/ft² (35 μm thick), suitable for most digital and low-power analog designs. Use 0.5 oz/ft² for fine-pitch traces requiring very narrow widths. Use 2 oz/ft² or heavier for power circuits carrying more than 1-2 A. Heavy copper (3-10 oz/ft²) is used in power electronics, automotive, and high-current applications.