PCB Trace Width Calculator — Minimum Width for Current Capacity
Find the minimum copper trace width required to safely carry a specified current within a temperature rise limit. Based on the IPC-2221 standard — select copper weight, layer type and allowable temperature rise to get the result in both mm and mils.
A
°C
Copper weight
Layer type
Minimum width to carry the specified current within the temperature rise limit (IPC-2221)
- 1
Temperature factor ΔT^0.44
10^0.44 = 2.7542 - 2
Required area A (mil²)
(2 ÷ (0.048 × 2.7542))^(1÷0.725) = 42.39Inverted IPC-2221 formula solves for the minimum cross-sectional area. - 3
Width in mils
42.39 ÷ 1.38 = 30.77 - 4
Minimum trace width (mm)
30.77 × 0.0254 = 0.781
How does this calculator work?
Minimum PCB trace width: W_mm = [(I / (k × ΔT^0.44))^(1/0.725)] / T_mils × 0.0254, where k = 0.048 (outer) or 0.024 (inner), per IPC-2221. For 2 A on 1 oz outer copper with 10 °C rise, minimum width ≈ 1.1 mm. Always add a safety margin above the calculated minimum.
Formula
How this is calculated
This calculator inverts the IPC-2221 current capacity formula. The standard gives I = k × ΔT^0.44 × A^0.725, where A is the cross-sectional area in square mils. Solving for A: A = (I / (k × ΔT^0.44))^(1/0.725). Since A = width × thickness, the minimum width is W = A / T, where T is the copper thickness in mils. Convert to millimetres by multiplying mils by 0.0254.
The constants k = 0.048 (external layer) and k = 0.024 (internal layer) come from the empirical fit in IPC-2221. External (outer) layers dissipate heat into the air above and below the PCB, so they can carry more current than internal traces surrounded by laminate. Allowable temperature rise (ΔT) is the key design choice — IPC-2221 recommends no more than 10 °C for most PCBs; 20–30 °C is sometimes used for dedicated power planes where component reliability is less sensitive to the trace temperature.
The width shown is the minimum — always add a safety margin (typically 20–50%) for layout deratings, current surges, hot ambient conditions, and manufacturing tolerances. The voltage-drop and resistance-per-cm values use the minimum calculated width at copper resistivity of 1.724 × 10⁻⁵ Ω·mm. The XY curve shows how required width scales with current, making it easy to see whether increasing copper weight (moving to 2 oz) or widening the trace is the more practical option.
Frequently asked questions
No — the IPC-2221 minimum is a floor, not a design target. Add at least a 20–50% margin for hot ambient conditions, start-up current surges and conservative derating. For safety-critical or automotive designs, IEC/automotive standards may impose stricter derating rules. The calculated width is also before any voltage-drop requirement — if drop matters, you may need an even wider trace.
The coefficient k is 0.048 for external layers but only 0.024 for internal ones — exactly half. Because current I scales with k × A^0.725 and the exponent is less than 1, halving k roughly doubles the required area, which means doubling the width (given fixed thickness). Internal traces are surrounded by insulating laminate that traps heat much more than the air around outer layers.
1 mil (thou) = 0.001 inch = 0.0254 mm. IPC-2221 uses mils throughout its formula; most modern CAD tools default to millimetres. This calculator shows both. Common design rules: 0.1 mm (≈ 4 mil) minimum trace in budget fabrication; 0.05 mm (≈ 2 mil) with advanced fabrication. The minimum width this calculator outputs often exceeds these limits for power traces, making the current limit — not the minimum manufacturable width — the binding constraint.
Also known as
TG we-Calculate Editorial Team. (2026). PCB Trace Width Calculator — Minimum Width for Current Capacity [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/pcb-trace-width-calculator
TG we-Calculate Editorial Team. "PCB Trace Width Calculator — Minimum Width for Current Capacity." TG we-Calculate. 2026. https://we-calculate.com/calculator/pcb-trace-width-calculator.
TG we-Calculate Editorial Team, "PCB Trace Width Calculator — Minimum Width for Current Capacity," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/pcb-trace-width-calculator
@misc{wecalculate_pcb_trace_width_calculator, title = {PCB Trace Width Calculator — Minimum Width for Current Capacity}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/pcb-trace-width-calculator}}, year = {2026}, note = {TG we-Calculate} }
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