ANSI IPC-2221A PCB Trace Width Calculator


ANSI PCB Trace Width Calculator

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New features in this version include:

  • use of metric or imperial units for all major fields
  • the ability to change units for any applicable field on the fly
  • minor enhancements to some of the calculations - IPC-2221(A) changes the curve fit
  • saving of all parameters in a cookie to keep your preferences between visits
ANSI PCB Trace Width Calculator
Input Data Results Data
    Internal Traces External Traces
Field Value Units Trace Data Value Units Value Units
Current (max. 35A) Required Trace Width
Temperature Rise (max. 100°C) Cross-section Area
Cu thickness Resistance Ω Ohms Ω Ohms
Ambient Temperature Voltage Drop Volts Volts
Conductor Length Loss Watts Watts
Peak Voltage Volts Required Track Clearance

This page calculates approximations to the ANSI / IPC-2221/IPC-2221A design standards for PCB trace width - this is the replacement for IPC-D-275.

The approximations and rationale are described in Trace Currents and Temperatures Revisited by Douglas Brooks, UltraCAD Design, Inc.

The figures returned by this calculator are to be taken as a guide only. I will not be held responsible for any mishap or loss, either direct or consequential, that may occur as a result of relying on the figures herein.

The trace width formulas are:

Internal traces : I = 0.024 x dT0.44 x A0.725
External traces: I = 0.048 x dT0.44 x A0.725


I = maximum current in Amps
dT = temperature rise above ambient in °C
A = cross-sectional area in mils²

Please note that IPC-2221(A) equations are subtly different from those in IPC-D-275 in that they are typically slightly more conservative and are impicitly derated to compensate for manufacturing effects, i.e. they should be more reliable in practice.

The values calculated here compare very closely with those derived by the UltraCAD PCBTEMP utility, and like the diagrams in the standards documents, are valid up to 35A for external traces and 17.5A for internal, 400mil widths and a maximum temperature rise of 100°C.

I've added a recommended track clearance value based on the UL rule:

clearance in inches = 0.023" + (0.0002" x V)

The formulae as it stands is simplistic, but is reasonable for V > 50. Note that there are many international standard for this sort of thing, e.g. EN60065:1994, which for European mains of 230V, allows for about 120mil for Class I (protected by earthing) and 240mil for Class II (double isolated). Note that if there is no conformal coating and the environment is dirty/humid/condensing then all bets are off. Please read the standards documents yourself.

Ideally, keep "hot" and "cold" areas of your board well apart.

Change a value in an input field, then press TAB to move to the next field. The results tables will be updated automatically.