PCB Trace Resistance Calculator

How to use this PCB trace resistance calculator

What this calculator does

This calculator estimates the DC resistance of a straight PCB conductor from its length, width, copper thickness, material resistivity, temperature coefficient, and ambient temperature. It uses the standard conductor relationship R = ρL/A with a first-order linear temperature correction referenced to 25 °C. The resulting resistance can then be combined with current through Ohm's law to estimate voltage drop. The model is a geometry-and-material estimate: it does not determine safe current capacity, trace temperature rise, AC skin effect, surface-roughness loss, connector resistance, via resistance, or the exact cross-section of an etched trapezoidal trace. For current-carrying design limits, consult the relevant printed-board design guidance such as IPC's PCB design standards overview.

When to use it

Use the calculator when checking DC power-distribution loss on a board, comparing the resistance impact of wider or heavier copper, estimating a small voltage drop before layout release, or examining how a different conductor material changes resistance. It is also useful for quick sensitivity checks: doubling length should double resistance, while doubling width or thickness should approximately halve it when the other inputs stay fixed.

How to calculate

1. The calculator opens with a complete demonstration: 10 mil width, 100 mm length, 1 oz/ft² copper, 25 °C, copper resistivity of 1.7 × 10⁻⁸ Ω·m, coefficient 0.0039/°C, and 1 A current. Results and a validated example XLSX are available immediately.
2. Replace the geometry values with your trace dimensions. Use the adjacent unit selectors; changing a unit converts the current value instead of merely relabeling it.
3. Keep the copper material values for a conventional copper estimate, or open “Resistivity properties and reverse solving” to enter another material's resistivity and temperature coefficient.
4. Enter either Current or Voltage drop. The most recently edited electrical field is held fixed and the other is recalculated using V = I × R.
5. Read Resistance (R), Voltage drop, and Current in the live results. Download Excel exports the current validated state. Reset clears the demonstration and all semantic data; after Reset, Excel export is disabled until a complete valid state is entered again.

Input guide

Trace width (W) is required unless you are reverse-solving it. Enter a positive decimal in mil, mm, or µm; 10 mil is the startup example. Increasing width increases cross-sectional area and reduces resistance. A common mistake is confusing mil with millimetre: 1 mil is 0.001 inch, not 1 mm.

Length (L) is required unless reverse-solved. Enter a positive decimal in mm, cm, or inches; the example uses 100 mm. Resistance scales directly with length, so a 200 mm route at otherwise identical conditions has about twice the resistance of a 100 mm route.

Trace thickness (T) is required unless reverse-solved. Choose oz/ft², µm, or mil; 1 oz/ft² is converted to 34.79 µm here. Larger thickness lowers resistance. Copper weight is an areal mass specification, so treating “1 oz” as a length without conversion is an interpretation error.

Ambient temperature is required unless reverse-solved and accepts °C or °F. The example is 25 °C, the reference temperature of this model. Higher temperature raises resistance when α is positive. This field is an assumed conductor temperature proxy; it does not predict self-heating.

Resistivity (ρ) at 25 °C is required unless reverse-solved. Enter a positive decimal or scientific-notation value in Ω·m or µΩ·cm. The copper example is 1.7 × 10⁻⁸ Ω·m. Different copper grades, plating, alloys, and measured conductors can differ, so use a material value appropriate to your design. NIST's historical Copper Wire Tables document standard resistivity and temperature-coefficient data for annealed copper.

Resistivity temperature coefficient (α) is required unless reverse-solved. It is entered in 1/°C, accepts decimal or scientific notation, and may be zero; the copper example is 0.0039/°C. A positive coefficient makes resistance increase with temperature. The linear coefficient is an approximation around the reference range, not a universal high-temperature material law.

Resistance (R) in the advanced panel is normally populated from the geometry. For reverse solving, type a positive target resistance in ohms and clear exactly one physical/material field. The calculator can algebraically recover that one missing value when the equation is solvable. Leaving multiple physical fields blank is underdetermined.

Current accepts a nonnegative decimal in A or mA; 1 A is the example. It does not change trace resistance in this model, but it directly scales voltage drop. Voltage drop accepts a nonnegative decimal in V or mV and is linked to current. Editing voltage makes voltage the held quantity and recalculates current. The underlying electrical units and relationships are part of the SI system described in the BIPM SI Brochure.

Output guide

Resistance (R) is the estimated DC trace resistance in ohms. Zero is not a valid result for positive finite geometry and resistivity; a very small value means the geometry/material combination is highly conductive. Voltage drop is the Ohm's-law product of current and resistance when current is the held electrical input. Current is the corresponding V/R result when voltage is held. The temperature correction is applied internally as the dimensionless multiplier 1 + α(Tamb – 25 °C), which equals 1 at 25 °C. The four header pills repeat the current width, resistance, current, and voltage drop so the key state remains visible while you edit.

Worked example

With a 10 mil width, 100 mm length, and 1 oz/ft² thickness, the calculator converts width to 0.000254 m and thickness to 0.00003479 m. At 25 °C the temperature factor is exactly 1, so using ρ = 1.7 × 10⁻⁸ Ω·m gives R = (1.7 × 10⁻⁸ × 0.1) / (0.000254 × 0.00003479) = 0.192380379 Ω. Displayed to six decimals, that is 0.192380 Ω. At 1 A, Ohm's law gives 0.192380 V of voltage drop. These values match the opening controls, live result cards, and workbook checkpoints.

Learn more

For a practical PCB-focused explanation of the same resistance relationship and temperature correction, see Polar Instruments' application note on calculating printed-circuit track resistance. For a separate current/trace-sizing context, DigiKey's PCB trace-width calculator documentation explains how resistance and voltage drop fit into broader trace design checks.