Conductor / Ampacity

In the following the factors influencing the current carrying capacity of circuit boards are named in context with heat development on the conductors, to provide practical guidance for implementation. In this complex topic, we can give you only a basic dimensioning feeling. If you need quite exact data, please use appropriate special software which takes into account: conductive pattern, layer structure and time (see TRM

Current carrying capacity of conductors acc. to IPC-2221

Maximum current [A] subject to the temperature increase in degrees [°]

2 Layers - 35µm copper

Trackwidth 10°20°30°40°50°60°
Trackwidth0.1mm 4mil10°0.4A20°0.6A30°0.8A40°0.9A50°1.0A60°1.1A
Trackwidth0.2mm 8mil10°0.7A20°1.0A30°1.2A40°1.4A50°1.6A60°1.7A
Trackwidth0.3mm 12mil10°0.9A20°1.3A30°1.6A40°1.8A50°2.0A60°2.2A
Trackwidth0.4mm 16mil10°1.1A20°1.5A30°1.9A40°2.2A50°2.4A60°2.7A
Trackwidth0.5mm 20mil10°1.3A20°1.8A30°2.2A40°2.5A50°2.8A60°3.1A
Trackwidth0.6mm 24mil10°1.4A20°2.0A30°2.4A40°2.8A50°3.1A60°3.4A
Trackwidth0.7mm 28mil10°1.6A20°2.2A30°2.7A40°3.1A50°3.5A60°3.8A
Trackwidth0.8mm 32mil10°1.7A20°2.4A30°2.9A40°3.4A50°3.8A60°4.1A
Trackwidth0.9mm 36mil10°1.8A20°2.6A30°3.2A40°3.7A50°4.1A60°4.5A
Trackwidth1.0mm 40mil10°2.0A20°2.8A30°3.4A40°3.9A50°4.4A60°4.8A
Trackwidth1.5mm 60mil10°2.5A20°3.6A30°4.4A40°5.1A50°5.7A60°6.2A
Trackwidth2.0mm 80mil10°3.0A20°4.3A30°5.3A40°6.1A50°6.8A60°7.5A
Trackwidth3.0mm 120mil10°3.9A20°5.6A30°6.8A40°7.9A50°8.8A60°9.7A
Trackwidth4.0mm 160mil10°4.7A20°6.7A30°8.2A40°9.5A50°10.6A60°11.6A
Trackwidth5.0mm 200mil10°5.5A20°7.7A30°9.5A40°10.9A50°12.2A60°13.4A
Trackwidth6.0mm 240mil10°6.1A20°8.7A30°10.6A40°12.3A50°13.7A60°15.1A
Trackwidth7.0mm 280mil10°6.8A20°9.6A30°11.7A40°13.6A50°15.2A60°16.6A
Trackwidth8.0mm 320mil10°7.4A20°10.4A30°12.8A40°14.8A50°16.5A60°18.1A
Trackwidth9.0mm 360mil10°8.0A20°11.3A30°13.8A40°15.9A50°17.8A60°19.5A
Trackwidth10.0mm 400mil10°8.5A20°12.1A30°14.8A40°17.0A50°19.1A60°20.9A

The calculation of the values is an approximation from the derived formulas of the IPC-2221 (see below). Deviation from DIN IEC 326 is due to the complexity of the topic. A rough estimate should always be possible.


The design guideline IPC-2221 (predecessor document: MILSTD 275) is the default data source for the DC temperature resistance of conductors. The measurements thereto come from the National Bureau of Standards (NBS) from the 1950s and refer to a 1.6mm thick PCB with a straight current-carrying conductor (thickness 35µm) and a 35µm Cu solid area on the back. They do not consider the surrounding medium (air pressure, motion), or the layout density.

In the 1960s the American magazine Design News published amended recommendations. In the mid-80s, in Germany the DIN IEC 326 comes out, which attends to this topic - the values obtained are quite similar to those from  the Design News (with all advantages and disadvantages).

The tables specified here can therefore only be used to roughly estimate the temperature development.

Formulas for calculating the maximum current

The formulas we use are based on the results of Oliver Betz ( and are an approximation from the formulas of the IPC, Design News and Dr. Johannes Adam.

I[A] = K  x h[mm]^0,5 x w[mm]^0,64 x ΔT[K]^0,5

I = current
K = fixed factor (2 layers: K = 3,3; 4 layers: K = 3,6)
w = conductor width
h = conductor height
ΔT = temperature increase in Kelvin (=temperature increase in degree °Celsius)

Please note: Despite careful checking of the formulas, we cannot grant any warranty for their accuracy!

The original* formula of IPC:

I[A] = 9,6 x A[mm²]^0,68 x ΔT[K]^0,43

A = w x h of the conductor

The original formula of Design News:
I[A] = 6,4 x A[mm²]^0,69 x ΔT[K]^0,45

*In the original IPC documentation no formulas are given, these were derived by e.g. Donald Brooks.

Tools and Software

Dr. Johannes Adam (formerly Flomerics) provides an easy to use 3D simulation software for printed circuit boards (TRM), further calculations and services in electronics cooling and thermal management:

Further tools, like for example the calculation of the resistance of vias can be found here (in German):

Fundamental works

Dr. Johannes Adam: "Neues von der Strombelastbarkeit von Leiterbahnen" (in German)

Friar, Michael E. and McClurg, Roger H., "Printed Circuits and High Currents", Design News, vol. 23 no. 25, 1968-12-06

Hoynes d.s., NBS Report 4283 "Characterization of Metal-Insulator Laminates", von 1956.

IPC-2221A (predecessor document: IPC-D-275 bzw. MIL-STD 275) >> new edition in IPC-2152

DIN IEC 326, "gedruckte Schaltungen, Leiterplatten, Gestaltung und Anwendung von Leiterplatten", issue 3/85