PCB Trace Width Calculator

By formulas from IPC-2221, PCB Trace Width Calculator can estimate the width of copper PCB boards and the trace required under the given current, and at the same time keep the rise in trace temperature not to exceed the limit. Note: The trace on the inner layer need to be much wider than the trace on the outer surface of the board. The results are estimates, actual results may vary depending on application conditions.

Current (I)
A
Ambient Temperature
°C
Thickness (t)
oz/ft²
Trace Length
in
Temperature Rise (TRise)
°C

Minimum Trace Width

Internal Layers: Minimum Trace Width

Internal Layers

Required Trace Width (W)
mil
Resistance
Ω
Voltage Drop
V
Power Loss
W

Minimum Trace Width

External Layers in Air: Minimum Trace Width

External Layers in Air

Required Trace Width (W)
mil
Resistance
Ω
Voltage Drop
V
Power Loss
W
FORMULA
First, calculate the Area:
A = (I / (k × TRiseb))1/c
Then, calculate the Width:
W = A / (t × 1.378)
For IPC-2221 internal layers:
k = 0.024, b = 0.44, c = 0.725
For IPC-2221 external layers:
k = 0.048, b = 0.44, c = 0.725
where k, b, and c are constants resulting from curve fitting to the IPC-2221 curves.
Common values:
Thickness: 1 oz
Ambient: 25 °C
Temp rise: 10 °C

Frequently Asked Questions

IPC-2221 is the generic standard for printed circuit board design, replacing the older IPC-D-275. It provides formulas derived from empirical data for correlating current carrying capacity, trace cross-sectional area, and temperature rise. The formula I = k × ΔT^0.44 × A^0.725 is used to calculate minimum trace width for a given current, where k=0.048 for external layers and k=0.024 for internal layers.

External layers (top/bottom) can dissipate heat into surrounding air via convection, providing 2× the current capacity of internal layers. Internal traces are sandwiched between FR-4 dielectric, which is a poor thermal conductor (0.25 W/m·K). Internal traces require approximately 2× the width of external traces for the same current and temperature rise.

Industry practice: 10°C rise for consumer electronics (ambient up to 40°C); 20°C rise for industrial equipment with good ventilation; 5°C or lower for high-reliability applications (automotive, medical, aerospace). Note that temperature rise is additive to ambient—if your device operates at 55°C ambient, a 10°C trace rise means 65°C copper temperature.

IPC-2221 provides conservative estimates suitable for most designs, but has limitations: it doesn’t account for thermal vias, adjacent copper pour, or forced air cooling (all of which improve current capacity). For high-power designs, consider IPC-2152 which uses more recent empirical data. Always add 10-20% safety margin to account for copper thickness variations in production.

For currents above 10A: 1) Use 2oz or heavier copper; 2) Consider parallel traces on multiple layers connected with thermal vias; 3) Add copper pour adjacent to power traces; 4) Use wide traces with thermal relief pads; 5) For extreme cases (>50A) consider busbars or external wiring. Always verify with thermal imaging during prototyping.

IPC-2221 (released 1998) is widely used and provides conservative estimates. IPC-2152 (released 2009) uses more recent empirical data and generally allows narrower traces for the same current. Use IPC-2221 when conservative design is needed or required by your PCB vendor; use IPC-2152 when space is tight and you can verify with thermal testing. This calculator uses IPC-2221 for maximum compatibility.

Trace length directly affects resistance, voltage drop, and power loss—but not the minimum width calculation. Longer traces of the same width have proportionally higher resistance (R = ρL/A). For power delivery, calculate voltage drop (V=IR) to ensure adequate voltage at the load. For logic signals, consider transmission line effects when trace length exceeds λ/10.

Need Help Manufacturing a High-Current PCB?

Trace width calculations are only one part of a high-current design. Copper weight, layer structure, thermal vias, copper balance, board thickness, and the final fabrication process also affect performance.

For heavy-copper, power, or aluminum-core PCB designs, send your current, copper thickness, board stackup, and thermal requirements for engineering review.