Read the width convention
Check whether the listed width applies to each panel or the pair combined. Then follow the seller's measuring instructions for the heading style you are buying. Gathered curtains need fabric beyond the flat width of the opening, but the appropriate amount depends on the product and desired finish. Do not apply one universal multiplier to every curtain design.
Measure the pole or track that will carry the curtains rather than assuming the window opening provides the right width. For the drop, use the starting point specified for the heading: eyelets, hooks and other fittings do not all hang from the same place. Note where the finished curtain should end and what lies below it.
Count the missing parts
Read whether hooks, rings, tiebacks or lining are included. An unlined pair and a lined pair are different purchases even when the fabric colour looks similar. If you need a particular level of light control, check the description of the exact product instead of assuming any dark-coloured curtain will provide it.
For a hypothetical comparison, two single panels at £18 each cost £36. A £32 pair is cheaper before delivery, but only if both options supply the dimensions and features you need. Add any necessary accessories or alteration quote rather than treating the displayed price as the completed window cost.
Inspect the size selection again at checkout, especially when one listing combines several widths and drops. If you are matching existing curtains, check colour and batch information where available and avoid relying on a screen image alone. Keep the order details until you have checked both panels. A complete, correctly measured pair is the useful unit of comparison, regardless of how prominently a smaller single-panel price appears in the sale.
