The microbending sensitivity of fibers was calculated as a function of the MAC value, which is the quotient of mode field diameter and cut-off wavelength. Two different methods, the expandable drum test and the sieve test, were used to simulate the additional losses due to microbending in fiber-optic cables. The theoretical and experimental results generally show an increase of the microbending sensitivity with increasing MAC value. In addition, the microbending loss of fibers strongly depends on the material and structure of the coating. Measurements of fibers in 'real' cables confirmed the predicted correlation between attenuation and MAC value.