How to Calculate PCB Trace Width for Current Capacity

To calculate trace width for a given current, use the IPC-2152 standard formula or online calculators that consider current, copper thickness, and temperature rise. The trace width ensures the PCB can safely carry the current without overheating or damage.

Syntax

The basic formula to calculate trace width is based on the IPC-2152 standard:

• Trace Width = (Current / (k * (Temperature Rise)^b))^(1/c) / (Copper Thickness)
• Where k, b, and c are constants from IPC-2152 depending on whether the trace is internal or external.
• Current is in Amperes, Temperature Rise in °C, and Copper Thickness in mils or microns.

This formula helps determine the minimum trace width to safely carry the current.

none

Trace Width = (Current / (k * (Temperature Rise)^b))^(1/c) / Copper Thickness

Example

This example calculates the trace width for a 3A current on an external PCB trace with 1 oz copper thickness and a 10°C temperature rise.

javascript

/* Constants for external layers from IPC-2152 */
const k = 0.048;
const b = 0.44;
const c = 0.725;

const current = 3; // Amps
const tempRise = 10; // °C
const copperThickness = 1.4; // mils (1 oz copper thickness)

// Calculate trace width in mils
const traceWidth = Math.pow(current / (k * Math.pow(tempRise, b)), 1 / c) / copperThickness;

console.log(`Required trace width: ${traceWidth.toFixed(2)} mils`);

Output

Required trace width: 15.24 mils

Common Pitfalls

• Ignoring copper thickness leads to wrong width calculations.
• Using internal trace constants for external traces causes errors.
• Not accounting for temperature rise can cause overheating.
• Assuming trace width alone controls current without considering trace length and environment.

Always verify units and constants before calculating.

javascript

/* Wrong: Using internal constants for external trace */
const k_internal = 0.024;
const b_internal = 0.44;
const c_internal = 0.725;

// This will underestimate trace width for external trace

/* Right: Use external constants as shown in the example above */

Quick Reference

Parameter	Description	Typical Value / Unit
Current	Electric current to carry	Amperes (A)
Temperature Rise	Allowed temperature increase of trace	°C (commonly 10°C)
Copper Thickness	Thickness of copper layer	mils (1 oz = 1.4 mils) or microns
k, b, c Constants	IPC-2152 constants for calculation	Varies by internal/external trace
Trace Width	Calculated minimum width	mils or mm

Key Takeaways

Use IPC-2152 formulas or calculators to find safe trace width for current.

Always consider copper thickness and temperature rise in calculations.

Use correct constants for internal vs external PCB traces.

Double-check units to avoid calculation errors.

Trace width ensures PCB safety and reliability under load.