When ordering new lenses the measurement that is universally needed is your ‘pupillary distance’, also known as pupil distance and PD. It is the distance between the centre of each pupil and ensures that when your lenses are made, the strongest focal point is aligned with the centre of your pupils.
People with high power in their script will need to have a very accurate measurement taken to avoid any distortion when looking through the lens, where the scripts are very high in a single vision lens, it’s worth taking a height measurement as well, just to ensure that you have the strongest power of the lens aligned with your pupil. If it is a mild script, a PD is only needed for single vision lenses as there is some leeway.
It’s not a difficult measurement to take, you will just need to visit your local optical store and any optician is able to do a quick measurement and provide it to you straight away. If you do have a heavier script, then you will most likely have to take the measurement with the frame on as you’ll also need heights.