Trace Width Calculator

Estimate trace width from current and permitted temperature rise. Compare external and internal layers using the historical IPC-2221 curve fit.

Calculate trace width Method & limits

LEGACY CURVE-FIT ESTIMATEI = k · ΔT⁰·⁴⁴ · A⁰·⁷²⁵

A is copper cross-section in mil².
This is not an IPC-2152 thermal solver.

Size the conductor, not just the artwork.

Use the finished copper thickness. A computed width is a starting point for thermal and fabrication review.

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Your inputs

Updates as you edit

Calculation

Current (A)Steady current magnitude; 0.001–35 A.

Existing trace width (mm)Used only for reverse current calculation.

Finished copper thicknessEnter the finished thickness, not an oz label.

Copper thickness unitChanging units preserves the thickness.

Permitted temperature riseThis is a temperature difference, not ambient.

Temperature-rise unit1–100 Δ°C equivalent is accepted.

Calculated locally in this browser. No inputs are uploaded.

Engineering estimate, not an ampacity approval. The fitted relationship omits your board’s cooling, planes, local neck-downs, vias and transient behavior. This calculator uses a historical IPC-2221 fit and does not model IPC-2152 thermal conditions.

A historical fit, clearly labeled.

The calculator uses the commonly implemented power-law fit to historical IPC-2221 current / temperature-rise curves. Coefficients and formula · KiCad calculator context

IPC-2152 addresses additional thermal construction and environmental variables. This historical IPC-2221 fit does not include those construction and environmental effects. IPC-2152 contents

I = k · ΔT^0.44 · A^0.725
A = [I / (k · ΔT^0.44)]^(1 / 0.725)
W = A / T

I: current, A (amperes)
ΔT: temperature difference, °C
A: conductor cross-section, mil²
W, T: width and copper thickness, mil
k = 0.048 external; 0.024 internal
1 mil = 0.0254 mm

Limits and interpretation

The chosen input envelope is 0.001–35 A, 1–100°C rise, 5–105 µm finished copper and up to 10.16 mm width in reverse mode. These guards do not establish accuracy across that envelope. A calculated width above 10.16 mm or reverse current above 35 A is flagged rather than presented as a validated recommendation.

The internal result is not simply double

For identical current, rise and thickness, the internal/external width ratio from this fit is 2^(1/0.725), approximately 2.6014. For identical width, the fitted internal current is half the external current. These statements describe the fit—not all real PCB constructions.

Review before release

Check the narrowest actual copper cross-section, fabrication tolerance, planes, vias, connector limits, board temperature and cooling. This tool has no ambient-temperature, airflow, pulse or heat-spreading model. Validate a production design with the applicable current standard, thermal analysis and testing.

Questions before
you use the result.

Know what the tool answers—and what still needs engineering review.

Does the result comply with IPC-2152?

No. It is a historical IPC-2221 curve-fit estimate. The model does not include the construction and thermal effects addressed by IPC-2152.

Can I enter 1 oz as the thickness?

No. Enter finished copper thickness in µm or mil. A nominal copper grade and a measured finished thickness are different inputs.

Can this size a via or a pulsed-current path?

No. The straight-trace fit does not model via barrels, pulses, duty cycle, fuses, connectors or local thermal bottlenecks.

Technical references & data basis

Check the linked manufacturer data and calculation references when using your results. Confirm the exact material grade and applicable document revision before production.