During continued loading the slow crack growth regions at the crack tip assume different shapes and sizes. Three different crack front profiles may be identified depending on the extent of crack growth, namely, parabolic, elliptical and semi-circular type. The crack front profile may be described by a parabola for relatively small crack growth, a large crack growth size leads to a semi-circular crack front profile while the intermediate stages of crack growth can be described by an elliptical crack front profile. An analytical optimization of offset measurement number ( N) for realistic crack growth size estimation for elliptical crack front profile is carried out considering two approaches, namely, offset measurement and area consideration. The variation of average crack size ( Δa av ) as well as convergence of ( Δa av ) with the offset measurement number ( N) is studied. The difference in Δa av obtained by both the methods is also investigated. Experimental verification of the crack growth front profile is carried out. Attempts are also made to study the effect of thickness, extent of crack growth, etc. on the value of N. In general 8–12 measurements are found to be adequate to have a realistic estimation of slow crack growth size for commonly used specimen thickness.