There are different models and how you measure these is shown here below. If you do not find the correct length you can choose one that is slightly longer. The diameter of the sleeve is the inner diameter.
You measure the length of the brake cable like this:
The direct wire is measured as follows:
Axle measurement + 700 mm = Length of the wire
The double wires are measured as follows:
One of the measurements shows the total length and the other the case.
For example, Double wire 2920/1230