The high spatial resolution of distributed fiber optic sensors enables quasi-continuous strain measurements, which makes it a promising technology for structural health monitoring. From this quasi-continuous strain data, location and width of cracks can be estimated. For major benefit to infrastructure maintenance, this crack width calculation is need to be automated. A frame-work for crack width estimation is presented, streamlining the different approaches for concrete and steel sensors, mainly differing in the compensation of tension stiffening. Relevant parameters for the analysis are identified and their influence is studied. Two sensors – a concrete embedded one and a reinforcement attached one – are used to estimate crack width using the presented framework. The results are compared to digital image correlation. Accurate estimates are achieved. Tension stiffening showed to have a negligible small influence on the estimated crack widths. The concrete embedded sensors have a higher sensitivity and are recommended for crack width monitoring.