The conversion of protein monomers into fibrils can be determined using the centrifugal filtration method. The results of this method were used to calibrate steady-shear birefringence and Thioflavin T fluorescence measurements. For both measurements, a linear correlation with the fibril concentration was extracted, resulting in two fast assays to determine the fibril concentration quantitatively. From birefringence measurements and the conversion determined using the centrifugal filtration method, we were able to calculate more precise values for the birefringence per unit length of the fibrils (M) and the flexibility of the fibrils (beta).