Copper Thickness

The most common unit of measure for the copper thickness on a printed circuit board is ounces (oz). But how thick is that? It's the resulting thickness when 1 oz of copper is pressed flat and spread evenly over a one square foot area. This equals 1.37 mils (1.37 thousandths of an inch). Of course not everyone thinks in mils so please refer to the chart below to convert into your preferred unit of measure.

1oz Copper Thickness Conversion
1 oz
1.37 mils (thousandths of an inch)
0.00137 inch
0.0347 mm
34.79 μm (micron/ micro meter)
*To determine the thickness of 4 oz,
simply mutiply 1 oz thickness x 4.

1.37mil x 4 = 5.48 mils = 4 oz

Most PCBs are constructed with 1 oz copper thickness. At PCB Transtek, if we are not given specific specs, we will assume 1 oz when quoting and building your design. If you have determined that your design requires more current than 1 oz can carry, you'll need to consider increasing the copper weight or increasing the width of your traces.
Here is a link to a current calculator: http://circuitcalculator.com/wordpress/?p=25/


Of course the thicker the copper the higher the cost, but there are certainly times where this is necessary. The cost increase is not only due to the raw material costs but processing thicker copper weights takes more time and is a little trickier to do. Keep the following chart in mind when designing your board. The more space you can allow between copper features the better. Etching the spaces (air gap) between traces is more difficult than etching a trace of the same width as your space.

General Guideline for Min Spacing
by Copper Weight
Cu Weight Min Recommended Space
Between Copper Features
1 oz 5 mils (0.127 mm)
2 oz 7 mils (0.178 mm)
3 oz 10 mils (0.254 mm)
4 oz 12 mils (0.305 mm)