PCB Trace Width Calculator
Estimate PCB trace width from current, finished copper thickness, permitted temperature rise, and internal or external layer location using IPC-2221-style empirical equations.
The calculator also estimates trace resistance, voltage drop, power loss, and operating temperature to support early PCB layout and power-routing decisions.
Engineering tool
PCB Trace Width Calculator
Estimate IPC-2221 trace width and calculate resistance, voltage drop, power loss, and trace temperature.
Continuous current carried by the trace.
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
- Required trace width
- 0.786154mm
- Required trace width
- 30.95096mil
- Cross-sectional area
- 0.02735mm²
- Resistance estimate
- 31.517009mΩ
- Voltage drop
- 63.034018mV
- Power loss
- 126.068035mW
- Estimated trace temperature
- 35°C
Use this as an initial external-trace estimate. Add margin for copper tolerance, connectors, vias, neck-downs, enclosure temperature, and board-level thermal conditions.
Formula reference
IPC-2221 PCB Trace Width 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.
Current capacity: I = k × ΔT^0.44 × A^0.725Required area: A = [I / (k × ΔT^0.44)]^(1 / 0.725)External trace coefficient: k = 0.048Internal trace coefficient: k = 0.024Trace width: W = A / tCopper resistance: R = ρ × L / AVoltage drop: Vdrop = I × RPower loss: P = I² × RVariable definitions
- I
- trace current
- ΔT
- allowed temperature rise
- A
- copper cross-sectional area
- t
- finished copper thickness
- L
- trace length
- ρ
- copper resistivity, 1.724 × 10⁻⁸ Ω·m
Worked Example
For a 2 A external trace with 1 oz copper, a 10 °C allowed rise, a 50 mm length, and 25 °C ambient:
A = [2 / (0.048 × 10^0.44)]^(1 / 0.725) ≈ 42.393 mil².
With 1 oz copper at approximately 1.37 mil thick, W ≈ 30.951 mil ≈ 0.786 mm.
The estimated resistance is 31.517 mΩ, giving about 63.034 mV drop and 126.068 mW loss. Estimated trace temperature is 35 °C.
Engineering Notes
Empirical estimate
IPC-2221 formulas are empirical estimates and should be treated as an initial sizing method.
Layer location
External traces dissipate heat better than internal traces, so internal copper generally needs more area.
Copper thickness
Copper thickness strongly affects required width; use the manufacturer's finished-copper value and tolerance.
Electrical loss
Voltage drop and power loss should be checked for high-current or long traces, including vias and neck-down regions.
Design verification
High-current PCB designs should be checked against manufacturer rules, IPC-2152 data where appropriate, thermal simulation, and prototype measurements.
Support reference
FAQ
How do you calculate PCB trace width?
The IPC-2221 approximation first calculates the required copper cross-sectional area from current and allowed temperature rise. Dividing that area by finished copper thickness gives the trace width.
What is the difference between internal and external trace width?
External traces dissipate heat into surrounding air more effectively. The IPC-2221 coefficient is therefore higher for external copper, while internal traces generally require greater width for the same current and temperature rise.
How does copper thickness affect trace width?
For a fixed required cross-sectional area, thicker copper reduces the necessary trace width. Finished copper thickness and plating variation should be confirmed with the PCB manufacturer.
What temperature rise should I choose?
The allowed rise depends on component limits, board material, enclosure temperature, nearby heat sources, and reliability targets. Conservative designs often begin with a modest rise and then verify the full thermal system.
Is IPC-2221 accurate for all PCB designs?
No. IPC-2221 is an empirical first estimate and does not model every stackup, copper pour, airflow, enclosure, via field, neck-down, or neighboring heat source. High-current designs require manufacturer review and thermal verification.
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