Trace Width to Current Calculator

Calculator Inputs

Trace Width

Width Unit

Copper Thickness

Thickness Unit

Allowed Temperature Rise °C

Trace Position

Trace Length

Length Unit

Ambient Temperature °C

Copper Resistivity Ω·m

Safety Percentage

Cooling Condition

Target Current A

Formula Used

This calculator uses the common IPC style trace current equation:

I = k × ΔT^0.44 × A^0.725

I is current in amperes. ΔT is allowed temperature rise in °C. A is cross sectional copper area in mil². A equals trace width multiplied by copper thickness. k is 0.048 for external traces and 0.024 for internal traces.

Resistance = ρ × L ÷ A

The tool also estimates hot resistance, voltage drop, power loss, current density, and target current margin.

How to Use This Calculator

Enter the PCB trace width and choose its unit.
Enter copper thickness as copper weight, mils, micrometers, or millimeters.
Set the allowed temperature rise for the design limit.
Choose external or internal trace position.
Add trace length to calculate resistance, voltage drop, and loss.
Enter a target current when you want a pass or fail margin.
Press the calculate button to show results above the form.
Use CSV or PDF export for records and design reviews.

Example Data Table

Trace Type	Width	Copper	Rise	IPC Current	80% Design Current
External	20 mil	1 oz	10 °C	1.464 A	1.171 A
External	40 mil	1 oz	20 °C	3.282 A	2.626 A
Internal	50 mil	2 oz	20 °C	3.189 A	2.551 A
External	100 mil	2 oz	30 °C	12.600 A	10.080 A

Why Trace Current Matters

A PCB trace is a small copper path. It behaves like a resistor. When current flows, the trace warms. Too much heat can damage copper, solder mask, parts, and nearby materials. Designers therefore estimate current before routing a board. The estimate is not a promise. It is a practical guide for safer layout choices.

Width, Thickness, and Heat Rise

Trace width is only one part of the answer. Copper thickness also matters. A wide thin trace may carry less current than a narrow heavy copper trace. Temperature rise sets the thermal limit. A larger allowed rise gives a higher current value. Internal traces usually carry less current because heat escapes poorly. External traces often cool better through air and copper exposure.

Using Results in Design

This calculator converts width and thickness into cross sectional area. It then applies the common IPC style equation. The result helps compare layouts quickly. You can add a target current to review margin. A safety percentage gives a more conservative design current. Voltage drop and power loss show how much energy becomes heat along the trace. These values are useful for power rails, motor drivers, battery paths, and LED circuits.

Practical Layout Tips

Use wider traces for high current nets. Keep power paths short when possible. Avoid sharp neck downs. Check connector pins, vias, planes, and solder joints too. A trace may be wide enough, but a via can still limit the path. For high current boards, use planes, pours, parallel traces, or heavier copper. Add thermal relief only where it helps assembly. Review manufacturing limits before choosing very narrow or very thick copper features.

Important Limits

Real boards vary. Copper plating, solder mask, airflow, stackup, altitude, and nearby heat sources change the final temperature. The equation is best for early estimates and comparison. For critical products, validate with testing, thermal imaging, and manufacturer guidance. Leave margin when the load is continuous. Use lower margin only when duty cycle, cooling, and measured temperatures support it.

Documentation Value

Saved reports help teams review assumptions later. Exported values can support design notes, client checks, and revision records. Keep the same units in drawings so reviewers can compare results without extra confusion and delay.

FAQs

What does this calculator estimate?

It estimates how much current a PCB trace can carry from width, copper thickness, temperature rise, and trace position. It also calculates resistance, voltage drop, power loss, current density, and target margin.

Which current equation is used?

It uses the common IPC style equation: I equals k times temperature rise to 0.44 times copper area to 0.725. External and internal traces use different k values.

Why do internal traces carry less current?

Internal traces are buried inside board material. Heat leaves them less easily than exposed outer traces. That is why the internal trace constant is lower in the formula.

What does copper weight mean?

Copper weight describes copper thickness. One ounce copper is about 1.378 mil, or about 35 micrometers. Heavier copper increases cross sectional area and current capacity.

What is a safe temperature rise?

Many designs use 10 °C to 20 °C for conservative routing. Higher rises may work, but they add heat and can affect nearby parts, solder joints, and board life.

Why add a safety percentage?

The safety percentage derates the calculated capacity. For example, 80% uses only part of the estimate. This gives margin for manufacturing variation, airflow changes, and continuous load.

Why does trace length matter?

Length does not change the IPC current capacity directly. It changes resistance, voltage drop, and power loss. Long traces can waste power even when their width can carry the current.

Can I export the result?

Yes. After calculation, use the CSV button for spreadsheet records. Use the PDF button for a simple report that includes the main input and output values.