Sodium alkyl sulfate micelles are predicted to grow as a power law of the total counterion salt concentration, Y-aq, in the aqueous phase as follows : N-A = kappa(2)(Y-aq)(gamma), where N-A is the micelle aggregation number and kappa(2) and gamma are constants which are estimated from the critical micelle concentration and the apparent degree of counterion attachment. For sodium dodecyl sulfate, N-A = 162(Y-aq)(1/4) is predicted and is shown to be in good agreement with aggregation numbers measured by a number of techniques over a wide range of Y-aq whether this quantity is varied by changing the concentrations of the detergent, the added counterion salt, or both. Values of kappa(2) and gamma are estimated for six members of the sodium alkyl sulfate family.