PCB Current Capacity Calculator
Estimate PCB trace current capacity from trace width, finished copper thickness, allowed temperature rise, and internal or external layer location.
The IPC-2221-style estimate also provides resistance, voltage drop, power loss, and trace temperature at the calculated current to support PCB power-routing decisions.
Engineering tool
PCB Current Capacity Calculator
Estimate IPC-2221 trace ampacity, resistance, voltage drop, power loss, and operating temperature.
Finished conductor width, excluding solder mask effects.
Finished copper thickness; 1 oz is approximately 34.79 µm.
Permitted trace temperature above ambient.
Electrical length used for resistance and voltage-drop estimates.
Expected local board or enclosure temperature.
Result console
- Estimated current capacity
- 2.38115A
- Cross-sectional area
- 0.03479mm²
- Trace resistance
- 24.777235mΩ
- Voltage drop at rated current
- 58.99832mV
- Power loss at rated current
- 140.483868mW
- Estimated trace temperature
- 35°C
Use this as an initial external-trace ampacity estimate. Apply margin for copper tolerance, vias, neck-downs, connectors, enclosure temperature, and airflow.
Formula reference
IPC-2221 PCB Current Capacity Formulas
The IPC approximation uses current in amperes, temperature rise in °C, and copper cross-sectional area in square mils. Resistance is calculated separately in SI units.
Copper area: A = W × tCurrent capacity: I = k × ΔT^0.44 × A^0.725External trace coefficient: k = 0.048Internal trace coefficient: k = 0.024Copper resistance: R = ρ × L / AVoltage drop: Vdrop = I × RPower loss: P = I² × RVariable definitions
- W
- trace width
- t
- finished copper thickness
- ΔT
- allowed temperature rise
- A
- copper cross-sectional area
- L
- trace length
- ρ
- copper resistivity, 1.724 × 10⁻⁸ Ω·m
Worked Example
For a 1 mm external trace with 1 oz copper, a 10 °C allowed rise, a 50 mm length, and 25 °C ambient:
The copper area is 1 mm × 0.03479 mm = 0.03479 mm², or approximately 53.925 mil².
I = 0.048 × 10^0.44 × 53.925^0.725 ≈ 2.381 A.
The estimated resistance is 24.777 mΩ, giving about 58.998 mV drop and 140.484 mW loss. Estimated trace temperature is 35 °C.
Engineering Notes
Copper area
Current capacity depends strongly on copper cross-sectional area and the permitted temperature rise.
Layer location
External layers carry more current than internal layers for the same width because they dissipate heat more effectively.
Model limits
IPC-2221 is an estimate and can differ from IPC-2152 data, detailed simulation, or field measurements.
Electrical loss
Long traces should also be checked for resistance, voltage drop, and power loss at the expected current.
Design verification
High-current designs should be verified with PCB manufacturer rules, complete stackup data, thermal testing, and suitable derating.
Support reference
FAQ
How much current can a PCB trace carry?
Current capacity depends on copper cross-sectional area, layer location, allowed temperature rise, surrounding thermal conditions, and design margin. This calculator provides an IPC-2221-style first estimate.
How does trace width affect current capacity?
A wider trace has more copper cross-sectional area, lowering resistance and allowing more current for the same estimated temperature rise. Thickness and finished-copper tolerance also affect the result.
Why do internal traces carry less current?
Internal traces are surrounded by laminate and generally dissipate heat less effectively than exposed outer-layer copper. IPC-2221 therefore uses a lower coefficient for internal traces.
What temperature rise should I use?
Choose a rise that keeps the trace, laminate, connectors, and nearby components within their thermal limits at worst-case ambient temperature. Conservative designs use margin and verify with testing.
Is IPC-2221 enough for high-current PCB design?
No. IPC-2221 is an empirical estimate. High-current designs should also consider IPC-2152 data, manufacturer capabilities, copper pours, vias, neck-downs, airflow, enclosure conditions, and measured board temperatures.
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