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PCB Trace Width Calculator

A = (I / (k·ΔT^0.44))^(1/0.725). 1 A, 1 oz, 10 °C external is 11.83 mil (0.3004 mm).

By Jasper · Updated

Calculator

PASS11.83 mil (0.3004 mm)R 84.03 mΩ at Tamb+ΔT

IPC-2221A §6.2. ρ = 1.7×10⁻⁶ Ω·cm at 25 °C, α-corrected to Tamb+ΔT. IPC-2152 is newer; 2221A is conservative.

Width
11.83 mil (0.3004 mm)
Area
16.3 mil²
R at Tamb+ΔT
84.03 mΩ
  • Pass External width: 11.83 mil (0.3004 mm), A = 16.30 mil²
  • Pass Trace resistance: 0.08403 Ω at 35 °C (ρ at 25 °C, α-corrected)

Formula

IPC-2221A §6.2 area

A=(IkΔT0.44)1/0.725) A = (I / (k · ΔT^0.44))^(1/0.725)

Width from thickness

W=At×1.378 W = A / (t_oz · 1.378 mil)

Variables

Symbol Meaning Unit Typical range Precision Default
I Current A ≥ 0 µA Curve fit quoted around I ≤ 35 A 4 sig 1 A
t Copper thickness oz/ft² ≥ 0 oz/ft² 1 oz/ft² = 1.378 mil (35 µm convention) 4 sig 1 oz/ft²
ΔT Temperature rise °C ≥ 0 °C Curve fit quoted for about 10–100 °C 4 sig 10 °C
Tamb Ambient temperature °C — 4 sig 25 °C
L Length mm ≥ 0 mm 4 sig 50 mm
k Layer (k = 0.048 external, 0.024 internal) — — 1 sig external
A Cross-section mil² — 4 sig —
W Trace width mil — 4 sig —
Wmm Trace width mm — 4 sig —
R DC resistance at Tamb+ΔT Ω — 4 sig —

Worked example

1 A, 1 oz, 10 °C external, 50 mm

Input Value
I · Current 1 A
t · Copper thickness 1 oz/ft²
ΔT · Temperature rise 10 °C
Tamb · Ambient temperature 25 °C
L · Length 50 mm
k · Layer (k = 0.048 external, 0.024 internal) external
Output Value
A · Cross-section 16.3 mil²
W · Trace width 11.83 mil
Wmm · Trace width 0.3004 mm
R · DC resistance at Tamb+ΔT 84.03 mΩ

Same, internal layer

Input Value
I · Current 1 A
t · Copper thickness 1 oz/ft²
ΔT · Temperature rise 10 °C
k · Layer (k = 0.048 external, 0.024 internal) internal
Output Value
W · Trace width 30.76 mil
Wmm · Trace width 0.7814 mm

How it works

Trace width is a current-and-temperature-rise question, not a “looks wide enough on the screen” one. The IPC-2221A fit is a closed form you can recompute, with a labelled 25 °C copper resistivity for the optional length.

Pick external or internal, enter current, copper weight and ΔT. Length is optional and only needed for DC resistance, drop and dissipation at Tamb + ΔT.

Pitfalls

  • IPC-2152 is the newer chart set. 2221A is more conservative and this page does not implement a 2152 closed form.
  • The curve fit is quoted around I ≤ 35 A, ΔT about 10–100 °C and width ≤ 400 mil.
  • Do not treat 1 oz as 1.4 mil or 34.1 µm here — the fit uses 1.378 mil.

FAQ

What resistivity does the resistance use?

1.7×10⁻⁶ Ω·cm at 25 °C, with α = 0.00393 /°C, evaluated at Tamb + ΔT.

Why is internal copper wider?

Internal k is 0.024, half the external 0.048, so the same current needs more area.

Is this IPC-2152?

No. IPC-2152 is newer. This page uses the IPC-2221A curve fit, which is conservative.

Can I enter thickness in µm?

Yes. The converter uses 1 oz = 1.378 mil = 35 µm convention.

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