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Electrical & Electronics

PCB Trace Width & Current Capacity Calculator

Estimate PCB trace width or current capacity, with copper thickness, resistance, voltage drop and power loss.

01

Your inputs

1 oz/ft² ≈ 35 µm

IPC-2221 estimate for uniform copper. Copper weight uses 1 oz/ft² ≈ 35 µm. Resistance and losses use 20 °C, not the heated trace temperature. Planes, vias, airflow and manufacturing tolerances are not modeled; verify your board design.

IPC-2221 · TI SNVA766 §11

02

Your results

Trace width
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Current capacity estimate
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Copper cross-section
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Resistance · 20 °C
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Voltage drop · 20 °C
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Trace power loss · 20 °C
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Formula—

Estimate trace capacity and check voltage loss

Use the displayed IPC-2221 curve fit to estimate trace width or current capacity. Review resistance, voltage drop and loss as separate checks. This simplified thermal model does not represent every board stackup or cooling condition.

Step by step

  1. Choose width sizing or current estimation, then select internal or external copper.
  2. Enter current or width, copper thickness and allowed temperature rise using the displayed units.
  3. Enter trace length and inspect width, current, resistance, drop and loss. Confirm the board's finished copper specification.

Settings and limits

Temperature rise
Rise is heating above the surroundings, not ambient temperature or an absolute operating limit.
Copper and layer
Layer choice changes the curve-fit coefficient. The oz input uses an approximate thickness conversion; verify actual copper thickness.
Trace length
Length changes resistance, drop and loss, not estimated current capacity. Resistance is for one copper trace at 20 °C.

Worked example

Use current-estimation mode with the dimensions below. Compare the external and internal layer results.

Example input

w = 1 mm; t = 35 µm; ΔT = 10 °C; ℓ = 100 mm
Expected result
kIR20VdropP
kext = 0.0482.391562 A49.26 mΩ117.808354 mV281.746006 mW
kint = 0.0241.195781 A49.26 mΩ58.904177 mV70.436502 mW

The internal-layer estimate is lower while resistance stays unchanged. Do not confuse current capacity with voltage-drop suitability.

Questions and troubleshooting

Why do layer results differ?

The model uses different thermal coefficients. Actual cooling also depends on stackup, nearby copper and airflow.

Is this a manufacturing clearance rule?

No. Check electrical spacing, fabrication minimums, vias and connector limits separately.

Is the calculated current a board rating?

No. Account for hot copper resistance, nearby heat sources and actual construction, then verify the board.