PCB Trace Resistance Calculator

Calculator Inputs

Trace Length

Length Unit

Trace Width

Width Unit

Copper Weight oz/ft²

Custom Thickness µm

Extra Plating Thickness µm

Current A

Supply Voltage V

Operating Temperature °C

Conductor Material

Custom Resistivity Ω·m

Custom Temperature Coefficient

Parallel Trace Count

Extra Allowance %

Frequency MHz

Formula Used

The calculator uses the standard conductor resistance equation:

R = ρL / A

Here, R is resistance in ohms. ρ is resistivity in ohm meters. L is trace length in meters. A is cross sectional area in square meters.

A = width × thickness

The temperature adjusted resistivity is:

ρT = ρ20 × [1 + α × (T - 20)]

Voltage drop is calculated as Vdrop = I × R. Power loss is calculated as P = I² × R. Copper thickness from copper weight uses about 34.798 µm per 1 oz/ft².

How to Use This Calculator

Enter the routed trace length from source to load.
Enter the minimum finished trace width.
Select copper weight or enter a custom finished thickness.
Add plating thickness when the board process increases copper height.
Choose conductor material or enter custom material values.
Enter operating current and supply voltage.
Add temperature, parallel traces, allowance, and frequency if needed.
Press calculate, then review resistance, voltage drop, and power loss.

Example Data Table

Length	Width	Copper	Current	Temperature	Approx Result
100 mm	10 mil	1 oz/ft²	1 A	25 °C	About 195 mΩ
75 mm	25 mil	2 oz/ft²	2 A	40 °C	About 34 mΩ
150 mm	0.5 mm	1 oz/ft²	0.5 A	60 °C	About 165 mΩ

Understanding PCB Trace Resistance

PCB trace resistance matters in every powered board. It affects voltage delivery, heat rise, and signal stability. A thin copper path can waste power when current is high. A long path can also drop voltage before the load receives it. This calculator gives designers a direct way to estimate those effects before fabrication.

Why Trace Size Matters

Resistance depends on length, width, thickness, material, and temperature. Wider traces have more cross section. They usually show lower resistance. Thicker copper also helps. Shorter routing keeps loss smaller. Temperature raises copper resistance, so warm boards need extra margin. The tool includes a temperature coefficient, so the result reflects real operating conditions.

Advanced Design Checks

The calculator also estimates current density, voltage drop, and power loss. These values help during regulator layout, motor driver routing, LED strip design, and battery board planning. Parallel traces can be modeled when current is shared across repeated copper paths. An allowance field lets you add margin for bends, vias, measurement tolerance, or plating variation. A frequency field gives a simple skin depth check for high speed or switching current.

Formula Accuracy

The main formula uses material resistivity multiplied by length and divided by cross sectional area. This is the standard direct current resistance model. The result is only as accurate as the entered dimensions. Finished copper can differ from nominal copper weight because etching and plating change the final profile. For critical boards, compare the result with manufacturer data and measured samples.

Practical Workflow

Start with the real routed length. Then enter the minimum finished trace width. Use the planned copper weight or a measured thickness. Add the operating temperature near the trace, not only room temperature. Enter the expected current. Review voltage drop and power loss first. If either value is too high, increase width, shorten the trace, use heavier copper, or split current through several paths.

Good Design Habits

Keep power traces direct and generous. Avoid narrow neck downs near connectors. Leave margin for fabrication tolerance. Use this tool early, then verify final constraints with thermal rules and board house capabilities. When layouts carry pulses, inspect peak current too. RMS current sets heating, while peak current affects voltage dips and noise.

FAQs

What does PCB trace resistance mean?

It is the electrical resistance created by a copper path on a circuit board. It depends on trace length, trace width, copper thickness, material resistivity, and temperature.

Why does copper thickness matter?

Thicker copper creates a larger cross sectional area. A larger area lowers resistance and reduces voltage drop. It can also reduce heat caused by current flow.

Can this calculator handle parallel traces?

Yes. Enter the number of parallel traces. The calculator divides total resistance by that count, assuming each trace shares current evenly and has similar geometry.

What is the allowance percentage?

The allowance field adds extra resistance margin. Use it for bends, vias, manufacturing tolerance, plating variation, or conservative design planning.

Does temperature affect trace resistance?

Yes. Copper resistance increases as temperature rises. The calculator adjusts resistivity using the entered temperature and material temperature coefficient.

What is skin depth used for?

Skin depth estimates how deeply high frequency current enters the conductor. At high frequency, effective conducting thickness may shrink, raising estimated resistance.

Should I use nominal or finished trace width?

Use finished trace width when possible. Fabrication can change final copper dimensions. Finished values usually give a more realistic resistance estimate.

Can this replace thermal design rules?

No. It estimates electrical resistance and power loss. For final boards, also check current capacity, copper temperature rise, airflow, stackup, and manufacturer limits.