# Track Width Calculator

This calculator can find the minimum PCB track width (external or internal layer) given the track current, the allowed temperatur rise, and copper layer thickness.

Calculated in accordance with the equations in IPC-2221A Section 6.2 (formerly IPC-D-275, the equation has not changed between these two standards amd you can get similar values by curve-fitting to the graphs provided in IPC-D-275, drawn in 1954, woah!).

$$I = k\Delta T^b A^c$$

where:
$$k$$ = 0.048 for external traces, 0.024 for internal tracks
$$\Delta T$$ = the change in temperature (temperature rise) in $$^{\circ}C$$
$$b$$ = 0.44
$$A$$ = cross-sectional area in $$mils^2$$
$$c$$ = 0.725

The standard only covers values where the current is 0-35A, track width is 0-10.16mm, temperature rise is from 10-100C, and the copper from 0.5-3oz. Values outside this range are extrapolated (and there more error-prone) and will turn orange.

This also assumes the track is sufficiently long enough the the end-points do not have a significant effect on the heatsinking. For example, this calcultor should not be used for calculating the width of thermal-relief style connections from a copper pour to a via, in where the track is very short (0.2-1.0mm). It also assumes there are no vias along the length of the track.

The current in assumed to be constant (DC). However, you can use the RMS value for a pulsed current as long as the pulses are fast enough.

The temperature of the PCB material should NEVER exceed the relative thermal index (RTI) of the material. This is defined in UL746B as the temperature at which 50% of the materials properties are retained after 100,000 hours.

Remember this calculator does not take into account other nearby heat sources.

 Variable: Value: Units: Trace Current Temp Rise Copper Thickness External Trace Internal Trace Minimum Track Width