Measurement of filter paper cellulase units per ml. Follow procedure as outlined in Figure 3. If filter paper (FP) activity for 0.5 ml of enzyme is equal to or less than 2.0, units per ml equal FP activity × 0.185. If the FP activity is greater than 2.0, repeat using diluted enzyme and estimate the ml of enzyme required to give a FP activity of 2.0. Units per ml equals 0.185/ml of enzyme to give a FP activity of 2.0.