In the USA, copper foil thickness is specified in units of ounces per square foot (oz/ft2), commonly referred to simply as "ounce". Common thicknesses are 1/2 oz/ft2 (150 g/m), 1 oz/ft2 (300 g/m), 2 oz/ft2 (600 g/m), and 3 oz/ft2 (900 g/m). These work out to thicknesses of 17.05 μm (0.67 thou), 34.1 μm (1.34 thou), 68.2 μm (2.68 thou), and 102.3 μm (4.02 thou), respectively. 1/2 oz/ft2 foil is not widely used as a finished copper weight, but is used for outer layers when plating for through holes will increase the finished copper weight Some PCB manufacturers refer to 1 oz/ft2 copper foil as having a thickness of 35 μm (may also be referred to as 35 μ, 35 micron, or 35 mic).