PCB Trace Current Calculator — IPC-2221 Max Current Capacity
Find out how much current a copper PCB trace can safely carry without exceeding a given temperature rise. Uses the IPC-2221 standard formula — enter trace width, copper weight, allowable temperature rise, and inner or outer layer to get the maximum current and resistance per centimetre.
mm
Copper weight
°C
Layer type
Per IPC-2221 (1998) — see IPC-2152 for updated values at higher currents
- 1
Cross-sectional area (mil²)
39.37 × 1.38 = 54.3Width and thickness converted from mm to mils (1 mm = 39.37 mil) before multiplication. - 2
Temperature factor ΔT^0.44
10^0.44 = 2.7542 - 3
Area factor A^0.725
54.3^0.725 = 18.0901 - 4
Maximum current (A)
0.048 × 2.7542 × 18.0901 = 2.39
How does this calculator work?
PCB trace max current: I = k × ΔT^0.44 × A^0.725 (IPC-2221), where k = 0.048 outer / 0.024 inner, ΔT = allowable temperature rise in °C, A = width × thickness in mil². A 1 mm wide, 1 oz outer trace with 10 °C rise carries about 1.6 A. Wider traces, thicker copper, and lower ΔT targets all shift the limit.
Formula
How this is calculated
Current flowing through a copper trace generates heat due to resistive losses. If the trace is too narrow, it overheats, damages the PCB laminate and can cause an open circuit. The IPC-2221 (1998) standard provides an empirical formula derived from experimental data: I = k × ΔT^0.44 × A^0.725, where A is the trace cross-sectional area in square mils (width × thickness), ΔT is the allowable temperature rise in °C above the ambient, and k is a constant (0.048 for exposed outer layers, which dissipate heat more easily, and 0.024 for inner buried layers).
The formula was derived from data at relatively low current densities. The IPC-2152 (2009) standard provides more accurate results for heavier copper and higher current situations, and is available as a set of charts and equations that account for copper weight more precisely. For a quick, conservative estimate on standard 1–2 oz copper traces up to a few amperes, IPC-2221 remains widely used and is a safe starting point.
Resistance per centimetre and voltage drop at maximum current are also shown, calculated from the copper resistivity of 1.724 × 10⁻⁵ Ω·mm. Note that copper resistivity increases with temperature — at 100 °C above ambient it is about 40% higher — so trace resistance at operating temperature will be somewhat higher than the 20 °C baseline value shown.
Frequently asked questions
A 10 °C rise is a conservative margin that keeps the trace well below FR4's glass-transition temperature (Tg ≈ 130–170 °C) and leaves headroom for ambient temperature variation, component heat sources, and current surges. For power-only traces away from temperature-sensitive components, 20–30 °C is commonly used in practice.
IPC-2152 (2009) supersedes IPC-2221 for current capacity calculations and gives more accurate results, particularly for heavier copper (2–6 oz) and higher currents. IPC-2221 tends to be conservative (under-estimates capacity) at high copper weights. For critical power designs, use IPC-2152 or a dedicated PCB current calculator that references its charts.
Yes — two parallel traces each carry half the total current, so the temperature rise in each trace is significantly lower. This is common for power rails where space constraints prevent a single wide trace. Ensure the traces are not immediately adjacent (so each can dissipate heat independently) and that vias and connectors also rate for the total current.
Also known as
TG we-Calculate Editorial Team. (2026). PCB Trace Current Calculator — IPC-2221 Max Current Capacity [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/pcb-trace-current-calculator
TG we-Calculate Editorial Team. "PCB Trace Current Calculator — IPC-2221 Max Current Capacity." TG we-Calculate. 2026. https://we-calculate.com/calculator/pcb-trace-current-calculator.
TG we-Calculate Editorial Team, "PCB Trace Current Calculator — IPC-2221 Max Current Capacity," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/pcb-trace-current-calculator
@misc{wecalculate_pcb_trace_current_calculator, title = {PCB Trace Current Calculator — IPC-2221 Max Current Capacity}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/pcb-trace-current-calculator}}, year = {2026}, note = {TG we-Calculate} }
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