If you are using a pole measure the distance between the finials.
If you have a track measure the total length of the track and then the distance from the corner at the end of the track to the wall (referred to as the return)
When using a pole the curtains should hang from directly under the wooden ring to the floor or sill.
When using a track the curtains should hang from the top of the track to the floor or sill.
We recommend that floor length curtains should be made to hang 1cm on the floor and that sill length curtains should hang to the sill or approx 5cm below the sill.
To be safe you should measure the length from each end of the track or pole and from the centre so uneven floors can be accommodated.
We would recommend that if there is any doubt or uncertainty the pole or track should be fitted before measuring for curtains.
NB Use a metal tape measure