MasterTool

PCB Trace Width Calculator

Size a PCB trace for a current using the published IPC-2221 formula for external or internal layers.

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What this tool does

Size a PCB trace for a current using the published IPC-2221 formula for external or internal layers. The IPC-2221 generic model assumes an isolated trace in still air. Board stack-up, planes, and neighbouring heat sources change real capacity — see IPC-2152 for production designs.

How to use the PCB Trace Width Calculator

  1. Enter or select trace location.
  2. Enter or select current (a).
  3. Enter or select copper weight (oz).
  4. Enter or select allowed temperature rise (°c).
  5. Read the calculated result; change any measurement to compare alternatives.

Formula

IPC-2221: area (mils²) = (I ÷ (k·ΔT^0.44))^(1/0.725), k = 0.048 external / 0.024 internal; width = area ÷ (oz × 1.378 mils)
location
Trace location
current
Current (A)
copper
Copper weight (oz)
rise
Allowed temperature rise (°C)

The IPC-2221 generic model assumes an isolated trace in still air. Board stack-up, planes, and neighbouring heat sources change real capacity — see IPC-2152 for production designs.

Worked example

For pcb trace width calculator, the following measurements illustrate the exact method: Trace location: external; Current (A): 2; Copper weight (oz): 1; Allowed temperature rise (°C): 10.

Inputs

  • Trace locationExternal layer
  • Current (A)2
  • Copper weight (oz)1
  • Allowed temperature rise (°C)10

Result

  • Minimum trace width (mils)30.76
  • Minimum trace width (mm)0.78
  • Required cross-section (mils²)42.39
  • Copper thickness (mils)1.38

Results explained

Minimum trace width (mils)
Minimum trace width (mils) from the formula above. The IPC-2221 generic model assumes an isolated trace in still air. Board stack-up, planes, and neighbouring heat sources change real capacity — see IPC-2152 for production designs.
Minimum trace width (mm)
Minimum trace width (mm) from the formula above. The IPC-2221 generic model assumes an isolated trace in still air. Board stack-up, planes, and neighbouring heat sources change real capacity — see IPC-2152 for production designs.
Required cross-section (mils²)
Required cross-section (mils²) from the formula above. The IPC-2221 generic model assumes an isolated trace in still air. Board stack-up, planes, and neighbouring heat sources change real capacity — see IPC-2152 for production designs.
Copper thickness (mils)
Copper thickness (mils) from the formula above. The IPC-2221 generic model assumes an isolated trace in still air. Board stack-up, planes, and neighbouring heat sources change real capacity — see IPC-2152 for production designs.

Frequently asked questions

Required cross-section (mils²) = (I ÷ (k × ΔT^0.44))^(1/0.725), with k = 0.048 for external layers and 0.024 for internal layers; width = area ÷ copper thickness. This tool implements that published generic formula.

Buried layers cannot shed heat to the air, so IPC-2221 gives them half the k factor — roughly double the cross-section for the same current and temperature rise.

About 1.378 mils (35 µm). 2 oz is twice that, so the same cross-section needs half the width.

10 °C is a conservative common choice; 20 °C is often acceptable. Remember the board's absolute temperature is ambient plus this rise, and nearby traces heat each other.

IPC-2221's current-capacity curves are widely used for estimates; the newer IPC-2152 is more detailed and accounts for board material and adjacent planes. For production boards, verify with your fabricator and IPC-2152 data.