What standard does this calculator use?

It uses the IPC-2221 empirical formulas: Width = Area / (Thickness × 1.378), where Area = (Current / (k × ΔT^b))^(1/c). The constants k, b, c differ for external (k=0.048, b=0.44, c=0.725) and internal (k=0.024, b=0.44, c=0.725) layers.

What temperature rise should I use?

A 10 °C rise above ambient is conservative and widely used for commercial designs. 20–30 °C is acceptable for less critical traces. For high-reliability or automotive designs, stay at or below 10 °C.

What is copper weight and how does it affect trace width?

Copper weight (oz/ft²) describes the thickness of the copper layer. 1 oz/ft² ≈ 35 µm (1.378 mil). Heavier copper (2 oz, 3 oz) lets you use narrower traces for the same current because the cross-sectional area is larger.

Why are internal traces wider than external ones for the same current?

External traces can dissipate heat into the surrounding air, while internal traces are buried in the laminate with much less thermal dissipation. The IPC-2221 constants reflect this difference, requiring wider internal traces.

Does this account for trace length or resistance?

No — this calculator focuses on thermal ampacity (minimum width to prevent overheating). For voltage-drop or impedance concerns, you also need trace length and resistivity calculations, which are separate analyses.

Is the result a minimum or recommended width?

It is the calculated minimum. In practice, add a 20–50 % margin for manufacturing tolerances, solder mask, and safety margin, especially for high-reliability applications.

PCB Trace Width Calculator

Enter current, temperature rise, and copper weight to find the minimum trace width per the IPC-2221 standard.

Trace Parameters

Current (A)

Maximum current the trace must carry continuously.

Allowable Temperature Rise (°C)

Typical values: 10 °C (conservative) to 30 °C (relaxed).

Copper Weight (oz/ft²)

Standard PCB copper thickness in ounces per square foot.

Layer Type

External Internal

External traces cool more easily; internal traces need more width.

Results

Enter parameters and click Calculate.

IPC-2221 Formula Reference

Area = (I / (k × ΔT^b))^1/c

Width = Area / (Thickness × 1.378)

External: k=0.048, b=0.44, c=0.725

Internal: k=0.024, b=0.44, c=0.725

Thickness (mils) = oz × 1.378

Summary

This calculator determines the minimum copper trace width needed to safely carry a specified current on a PCB, based on the IPC-2221 standard. It accounts for both external (outer layer) and internal (inner layer) traces, copper weight, and the allowable temperature rise above ambient. Accurate trace sizing prevents overheating and delamination in PCB designs.

How it works

Enter the maximum current (in amps) the trace must carry.
Set the allowable temperature rise above ambient (typically 10–20 °C).
Choose the copper weight (thickness) in ounces per square foot.
Select whether the trace is on an external or internal layer.
Click Calculate — the tool applies the IPC-2221 formula and returns the minimum trace width in mils and millimeters.
Review the cross-sectional area and current density shown for reference.

Use cases

Size power traces on motor driver and power supply boards.
Verify that existing trace widths are adequate for the expected current.
Design USB, battery, or solar charge controller PCBs.
Meet IPC-2221 compliance requirements for manufactured boards.
Compare internal vs. external layer requirements during layer stackup planning.
Estimate copper area needed for high-current bus bars on the PCB.

Frequently Asked Questions

Last updated: 2026-05-29 · Reviewed by Nham Vu