The standard definition for Etch Factor is to specify it as the ratio of  trace thickness / amount of over-etching. This gives the following formula:

Etch Factor = T/[0.5(W1-W2)]

例如，W1 = 5.2mil， W1 = 4.2mil， T = 3.7mil， 则

Etch Factor  = 3.7/[0.5(5.2-4.2)] = 7.4

有的时候也会使用角度α来表示蚀刻因子，α = ATAN(7.4) = 82.304°