PCB Trace Resistance Calculator

Estimate resistance, voltage drop and resistive power loss for one rectangular copper trace carrying DC. Cross-section A = width × thickness; R = ρL/A; voltage drop = IR; power loss = I²R. The engine uses ρ(T) = 1.7241 × 10⁻⁸ × [1 + 0.00393 × (T − 20)] Ω·m.

Assumptions & limits

• Enter length and width in mm, copper weight in oz/ft², current in A and copper temperature in °C. Length, width, copper weight and current must be finite and greater than zero. There is no fixed upper input limit, but calculations outside the finite positive numeric range are rejected.
• Temperature must be finite and give a positive temperature multiplier: 1 + 0.00393 × (T − 20) > 0 (approximately T > −234.453 °C). This is a mathematical guard, not a material operating-temperature specification. The page starts at 20 °C.
• This model converts 1 oz/ft² to 34.79 µm of thickness. This fixed conversion is a calculator assumption; enter the nominal copper weight, not a thickness in µm.
• The calculation uses a uniform cross-section and the temperature you supply. It does not solve self-heating, current capacity, AC impedance, vias, connectors or manufacturing variation.

100 mm long, 1 mm wide, 1 oz/ft² copper, 2 A and 20 °C.

1. Thickness = 1 × 34.79 = 34.79 µm. Area = 1 × 0.03479 = 0.03479 mm² = 3.479 × 10⁻⁸ m².
2. At 20 °C the temperature multiplier is 1. R = (1.7241 × 10⁻⁸ × 0.1) ÷ (3.479 × 10⁻⁸) = 0.049557344… Ω.
3. Voltage drop = 2 × R = 0.099114688… V. Power loss = 2² × R = 0.198229376… W.

49.557344 mΩ resistance, 0.099115 V drop and 0.198229 W loss (rounded).

A width of 0 mm is rejected because the cross-section would be zero. Current of 0 A is also rejected by this version, even though the ideal equations would give zero voltage drop and power loss. A temperature of −250 °C is rejected because the linear model would produce negative resistivity.

Resistance describes this trace segment only. Voltage drop is the voltage lost along it at the entered current; power loss is the electrical power dissipated in it. These outputs do not establish an allowable temperature rise or a safe current rating. A return trace or connector needs its own contribution.

• Conductor resistance R = ρL/A, voltage drop IR and resistive power I²R; the interpretations of voltage drop and power loss follow from these equations. IEC 60050 — International Electrotechnical Vocabulary (Electropedia)
• Annealed-copper reference resistivity at 20 °C and the 0.00393/°C linear temperature coefficient used in this model. IEC 60028 — International standard of resistance for copper

The copper-weight conversion, input guards and omitted effects above describe this implementation. The synthetic example is arithmetic under these assumptions, not a measured board or a fabrication tolerance.