PCB Trace Width Calculator

This free PCB trace width calculator uses the IPC-2221 formula to find how wide a printed circuit board trace must be to carry a given current without overheating. Choose the copper weight (0.5, 1, 2 or 3 oz), the allowed temperature rise and whether the trace is on an outer or inner layer. It also gives the trace's resistance, voltage drop and power loss for your trace length — useful for power rails, motor drivers, LED strips and battery circuits.

IPC-2221 trace width formula

Area (mil²) = (I ÷ (k × ΔT^0.44))^{1 ÷ 0.725}
Width (mil) = Area ÷ (copper oz × 1.378)
k = 0.048 for external layers, 0.024 for internal layers

I is the current in amps and ΔT the temperature rise in °C above ambient. Resistance uses copper's resistivity at 25 °C plus the temperature rise. The formula is based on IPC test data for currents up to 35 A (external) and 17.5 A (internal) and widths up to 400 mil.

Worked example

For 2 A on an outer 1 oz layer with a 10 °C rise: area = (2 ÷ (0.048 × 10^0.44))^1.379 ≈ 42 mil², so the width is 42 ÷ 1.378 ≈ 0.78 mm (31 mil).

PCB trace width chart (10 °C rise)

Current	1 oz external	2 oz external	1 oz internal
0.5 A	0.12 mm (5 mil)	0.06 mm (2 mil)	0.3 mm (12 mil)
1 A	0.3 mm (12 mil)	0.15 mm (6 mil)	0.78 mm (31 mil)
2 A	0.78 mm (31 mil)	0.39 mm (15 mil)	2.03 mm (80 mil)
3 A	1.37 mm (54 mil)	0.68 mm (27 mil)	3.56 mm (140 mil)
5 A	2.77 mm (109 mil)	1.38 mm (54 mil)	7.19 mm (283 mil)
10 A	7.19 mm (283 mil)	3.6 mm (142 mil)	18.71 mm (737 mil) *
15 A	12.59 mm (495 mil) *	6.29 mm (248 mil)	32.74 mm (1,289 mil) *
20 A	18.71 mm (737 mil) *	9.36 mm (368 mil)	—

Currents beyond the IPC-2221 chart range are left blank, and * marks widths above the 400 mil the data covers. For very high currents use copper pours, multiple layers in parallel, thicker copper or bus bars, and check vias: a single standard via carries only around 1 A.

Related calculations

Sizing the wires that feed the board? Use the wire size and voltage drop calculator.
Work out a load's current from its power with the Ohm's law calculator.

Frequently asked questions

How wide should a PCB trace be for 1 amp?

For 1 A with a 10 °C temperature rise on 1 oz copper, IPC-2221 gives 0.3 mm (12 mil) on an outer layer and 0.78 mm (31 mil) on an inner layer. Many designers use 0.3–0.5 mm (12–20 mil) for 1 A outer traces to leave margin.

How wide should a PCB trace be for 2 A or 5 A?

On an outer layer with 1 oz copper and a 10 °C rise: 2 A needs 0.78 mm (31 mil) and 5 A needs 2.77 mm (109 mil). Doubling the copper to 2 oz roughly halves the width: 1.38 mm (54 mil) for 5 A.

How thick is 1 oz copper on a PCB?

One ounce of copper spread over one square foot is about 35 µm (1.37 mil) thick. 0.5 oz is about 17.5 µm, 2 oz about 70 µm and 3 oz about 105 µm. Outer layers are often plated up from 0.5 oz to about 1 oz during manufacturing.

Why do internal traces need to be wider?

Inner-layer traces are surrounded by laminate, which conducts heat poorly, so they get hotter at the same current. IPC-2221 uses half the constant (0.024 instead of 0.048), which makes internal traces roughly 2.6 times wider for the same current and temperature rise.

What temperature rise should I use?

A 10 °C rise is the usual conservative choice. 20 °C is common for power traces where the board has room to run warmer, and gives a noticeably narrower trace. Consider the ambient temperature, nearby components and the board material’s maximum operating temperature.

What is the difference between IPC-2221 and IPC-2152?

IPC-2221 uses a simple formula based on old test data and is conservative for inner layers. IPC-2152 is a newer standard based on more extensive testing that also considers board thickness, copper planes and material; it often allows narrower inner traces. IPC-2221 remains the standard quick-calculation method.