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Full changelogEngine 1.18.3

Trace Width

PCB & Copper

Conductor width for a current and temperature rise, with resistance and drop.

Inputs

Board profile

Fills Copper weight and Ambient temperature from your board profile.

A
10 °C conservative · 20 °C typical · 30–45 °C for short outer runs
°C
°C
V

Results

Required width w

Not judged: sized to exactly your 20 °C rise. Check the voltage drop below.

35.54 mil · cross-section 48.7 mil² = 0.03142 mm²
0.9028mm
Show working
  1. Cross-section from IPC-2221A = (I / (k × ΔT^0.44))^(1/0.725) = (3 / (0.048 × 20^0.44))^(1/0.725) = 48.7 mil²
  2. Width from cross-sectionw = A / t = 48.7 mil² / 1.37 mil = 35.54 mil = 0.9028 mm
  3. Resistance at the conductor temperatureR = ρ(45 °C) × l / A = 18.9 nΩ·m × 50 mm / 0.03142 mm² = 30.13 mΩ
  4. Voltage dropV = I × R = 3 A × 30.1 mΩ = 90.4 mV
Trace resistance R

at 45 °C, 55.4 squares × 544 µΩ/sq
30.13mΩ
Voltage drop Vdrop

1.81 % of rail
90.4mV
Current density
95.5A/mm²
All results (4)
Temperature rise ΔT

conductor at 45 °C in 25 °C ambient
20.0°C
Current I
3A
Self-heating power
271.2mW
Sheet resistance

1 oz at 45 °C
544µΩ/sq
ΔT = 10 °CΔT = 30 °CΔT = 45 °Cyour ΔT = 20 °C

Accuracy

Source
  • IPC-2221B §6.2 (2012)

IPC-2221B, Generic Standard on Printed Board Design, §6.2 (2012) fitted to measurements

Valid range
  • Current at most 35 A
  • Allowable temperature rise 1 °C to 100 °C

Current The IPC-2221 charts stop at 35 A. Above that the curve is an extrapolation. IPC-2221B §6.2

Allowable temperature rise The charts cover rises of about 1 to 100 °C above ambient. IPC-2221B §6.2

Precision
A curve fit to measurements on bare boards in still air.

A plane underneath runs cooler; a sealed enclosure runs hotter. Use it as a starting width.

IPC-2221B §6.2

Verified against

2 independent cases. See the working.

This is a design aid. The engineer remains responsible for the design and for checking the standard itself.

Parameter sweep

Vary one input over a range and see the answer and verdict at each step, as a table and a curve.Pro

Worst-case corners

Put a tolerance on each input and get the worst-case band around the answer.Pro

Cross-section

The principle

A trace heats until its I²R loss equals the heat it sheds. IPC-2221 reduces that balance to one empirical curve, fitted to measurements on bare boards.

IPC-2221 current capacity
I=k ΔT0.44 A0.725I = k\,\Delta T^{0.44}\, A^{0.725}
A in mil², ΔT in °C above ambient, I in amperes. k = 0.048 external, 0.024 internal.
Rearranged for cross-section
A=(Ik ΔT0.44)1/0.725A = \left(\frac{I}{k\,\Delta T^{0.44}}\right)^{1/0.725}
Width from cross-section
w=AtCu,tCu  [mil]=1.37×oz/ft2w = \frac{A}{t_{Cu}}, \qquad t_{Cu}\;[\t{mil}] = 1.37 \times \t{oz/ft}^2
Resistance at temperature
R=ρ20[1+α(T−20)]lw tCuR = \frac{\rho_{20}\left[1+\alpha (T-20)\right] l}{w\,t_{Cu}}
ρ₂₀ = 1.724 × 10⁻⁸ Ω·m, α = 0.00393 /°C. A 60 °C rise adds about 24 % to the resistance.
Sheet resistance
R□=ρtCu≈0.5  mΩ/sq for 1 ozR_{\square} = \frac{\rho}{t_{Cu}} \approx 0.5\;\t{mΩ/sq for 1 oz}
Count the squares, l/w, and multiply by the sheet resistance.
  • IIcontinuous RMS current
  • ΔT\Delta Tallowable temperature rise above ambient
  • AAcopper cross-section, width × thickness
  • kk0.048 external / 0.024 internal
  • tCut_{Cu}copper thickness, 1 oz/ft² = 34.8 µm = 1.37 mil
More detail

ΔT is measured above local ambient. Inside a sealed enclosure that may already be 30 °C above the room. For a 30–45 °C rise, keep TA + ΔT well below the laminate Tg and check the neighbouring parts.

IPC-2221 and IPC-2152

IPC-2221 is a single curve that knows nothing of your stack-up. IPC-2152 (2009) uses newer measurements. A nearby plane, the board thickness and the laminate can change the answer by a factor of two or more, usually towards a narrower trace. Design to IPC-2221; justify anything narrower with IPC-2152 charts or thermal simulation.

Check the narrowest point. Vias and pad necks in the path often limit the current before the trace does.
References: IPC-2221B Generic Standard on Printed Board Design, §6.2 and Figure 6-4; IPC-2152 Standard for Determining Current-Carrying Capacity in Printed Board Design.

Engine version ⁨1.18.3⁩