Sheet resistance is a popular and convenient integrated circuits concept. The resistance of a strip of material is given by

R = ρL/A,

where ρ is the material's resistivity, L is the strip's length, and A is the strip's cross-sectional area. Ideally, each layer in an integrated circuit has no thickness variation across the wafer. The resistance can then be rewritten as

R = (ρ/t)(L/W) = R_{s}(L/W),

where R_{s} is the *sheet resistance* of the film. Thus the resistance of a strip in an integrated circuit is fully characterized by its sheet resistance and its aspect ratio, L/W.

The concept of sheet resistance can also be applied to the ion implanted regions of a crystalline wafer, even though the resistivity of these regions varies with thickness. In this case, the sheet resistance is very well approximated by

R_{s} = 1 / ∫^{T}dt/ρ(t),

where the lower limit is the wafer surface and T (this integration limit is rather arbitrary) is the point at which the implantation doping concentration has fallen to the wafer's background doping concentration.