Definition
Copper weight specifies how thick the copper foil on a PCB layer is, expressed in ounces per square foot (oz/ft2). The unit is historical: it is the weight of copper that, spread uniformly over one square foot, yields a given thickness. One ounce of copper corresponds to roughly 1.4 mils, or about 35 microns, of thickness. Two-ounce copper is twice as thick, about 2.8 mils (70 microns), and so on.
Why thickness matters
Thicker copper means greater cross-sectional area for every trace and plane, which raises current-carrying capacity and improves heat spreading. As a rough guide, a 10-mil-wide trace in 2 oz copper can carry roughly 2A for a 10C temperature rise, where the same trace in 1 oz copper carries less. Heavier copper also lowers DC resistance, reducing voltage drop on power-delivery paths. The trade-offs are cost, and that thicker copper is harder to etch finely, so very fine traces and tight spacing are easier to achieve in 0.5 oz or 1 oz copper.
Choosing copper weight
One-ounce copper is the default for general signal and logic boards. Two-ounce and heavier copper is chosen for power electronics, high-current rails, and boards that must dissipate significant heat, which is why power-handling sections of mining hardware often use heavier copper. When repairing a board, sizing a replacement jumper or estimating a trace's safe current first requires knowing the original copper weight, since it sets the baseline cross-section.
Copper weight is a primary input to trace current capacity and affects how well the power plane delivers current.
In Simple Terms
Copper weight specifies how thick the copper foil on a PCB layer is, expressed in ounces per square foot (oz/ft2). The unit is historical: it…