PCB Trace Resistance Calculator

Calculate copper PCB trace resistance, voltage drop, and power loss from trace dimensions, copper weight, current, and temperature.

Use standard copper resistivity with a temperature correction to check whether a board trace meets your electrical loss budget.

Enter the finished copper dimensions and operating conditions.

Trace Width (mm)

Copper Weight (oz/ft²)

Trace Length (mm)

Current (A)

Copper Temperature (°C)

About PCB trace resistance

A printed circuit board trace is a thin copper conductor, so it has measurable electrical resistance even though copper is highly conductive. Resistance depends on the conductor length, cross-sectional area, material resistivity, and operating temperature. This calculator models a rectangular copper trace and applies the fundamental relation R = ρL / A. Length is converted from millimetres to metres, while trace width and copper thickness form the cross-sectional area. Standard one-ounce copper is treated as approximately 0.0348 mm thick. Copper resistivity at 20°C is approximately 1.724 × 10⁻⁸ ohm-metres. Copper becomes more resistive as it warms, so the calculator adjusts resistivity with a temperature coefficient of 0.00393 per degree Celsius. This correction matters in power electronics because self-heating can increase voltage loss and create a feedback effect. Finished copper thickness can differ from its nominal foil weight after plating and fabrication, so use the board manufacturer's finished value when tight tolerances matter. Voltage drop follows Ohm's law: V = IR. Power converted to heat follows P = I²R. A trace that looks acceptable at a small current can therefore waste substantially more energy when current doubles, because heating rises with the square of current. Compare the calculated drop with the allowable tolerance at the load. Low-voltage digital rails, current-sense paths, motor drivers, LED supplies, and battery circuits often require especially small losses. The result is a DC resistance estimate for a uniform straight trace. It does not include vias, connectors, neck-down regions, solder joints, copper roughness, or contact resistance. At high frequencies, skin effect and proximity effect can increase effective resistance, while nearby copper pours and plated surfaces can change both electrical and thermal behavior. Add those elements separately or use a field solver when working with RF structures. For practical design, calculate the complete outbound and return path rather than only one segment. Leave margin for manufacturing variation, elevated enclosure temperature, and transient current. The resistance calculator is useful for early sizing and loss checks, but thermal limits should also be evaluated with an IPC-based current-capacity method and confirmed on representative hardware.

PCB trace resistance examples

Typical copper trace scenarios calculated at 20°C.

Trace	Calculated result	Design note
1 mm wide, 100 mm long, 1 oz, 1 A	0.04954 Ω, 0.04954 V	A common short power trace with about fifty millivolts of drop.
2 mm wide, 50 mm long, 2 oz, 3 A	0.006194 Ω, 0.01858 V	Wider, heavier copper sharply reduces resistance and loss.
0.25 mm wide, 200 mm long, 1 oz, 0.1 A	0.3963 Ω, 0.03963 V	A long narrow signal trace has noticeable resistance despite low current.

How to calculate PCB trace resistance

Enter the finished trace width and total electrical path length in millimetres.
Enter the copper weight; use 1 oz for standard 35 µm copper unless your fabrication stackup specifies another value.
Enter the expected current and copper operating temperature.
Select Calculate and compare resistance, voltage drop, and power loss with your design limits.

PCB trace resistance FAQ

How is copper weight converted to thickness?

One ounce per square foot of copper is approximately 0.0348 mm, or 35 µm, thick. The calculator scales that thickness linearly for other copper weights.

Why does trace resistance increase with temperature?

Thermal vibration in copper impedes electron flow more strongly at higher temperatures. Near room temperature, resistance rises by about 0.393 percent for each degree Celsius.

Should I include the return trace length?

Yes, a circuit current must travel through both the supply and return paths. Calculate each path and add the resistances, or enter their combined length when their widths and copper thicknesses match.

Does this calculator include via resistance?

No, the model covers only a uniform rectangular trace. Add via barrel, connector, neck-down, and contact resistances separately for a complete path estimate.

Is this result valid for high-frequency traces?

It is a DC resistance estimate and remains a useful baseline. At high frequencies, skin effect, surface roughness, and proximity effects can raise effective resistance, so RF designs may require a field solver.