Measure the fitting first
Confirm whether you are using a pole, track or another fitting. Measure from the point at which the chosen heading will hang, rather than automatically measuring from the top of the window.
Check the width and panel count
The total fabric width affects how full the curtains look when closed. Read whether the listed width is for one panel or a pair. Do not infer the number of panels or the heading type from a room photograph.
Choose the finished drop
Decide whether you want the fabric above a sill, below it or near the floor, then measure several points. Floors and ceilings may not be perfectly level. Leave clearance from heaters and other heat sources.
Confirm the fabric properties
Light filtering, blackout performance, lining and washability are separate product properties. Ask for clarification if they are missing from the listing. Keep a note of the final measurements so the chosen specification can be checked before dispatch.