Choke Line Friction is one of critical figures that personnel on the rig need to know and this numbers can be determined.
The procedures for the choke line friction determination are as follows;
1. Line up to circulate into choke line
Figure 1 - Line Up
2. Circulate down the choke line and up into riser. This will not add significant pressure to bottom hole. When you measure the pressure you need to know mud density and rheology and it is very important that you wait until you get the stabilized pressure reading.
Figure 2 – Circulate down choke line
3. Record CLF at expected kill rates for well control as 10 SPM, 20 SPM, 30 SPM, etc. This will give you an idea how much CLF at particular flow rate. The table below demonstrates the pre-recorded CLF
Flow Rate (SPM) Choke Line Pressure (psi) Mud Weight (ppg)
Table 1 Pre Recorded CLF
This procedure can be performed any time while drilling and we recommend you to check the CLF when drilling fluid properties have been changed a lot from the previous test. Additionally, you can use the same procedure to measure the frictional pressure at the kill line too.
Reference books: 
Well Control Books