Measure from the intended hanging system, not simply from the glass, when choosing curtains. The rod or track position, the heading style and the coverage you want determine how the fabric will sit. A window measurement alone leaves several important choices unresolved.
First decide what the curtain needs to do: provide the intended coverage, allow a useful opening and fit the surrounding room. Note nearby furniture and any fixed feature that affects where fabric can hang. Choose a suitable installation arrangement using its instructions before converting the plan into a curtain order. If installation is not yet decided, keep the measurements provisional rather than buying fabric around an assumption.
Width is more than the opening
Measure the span that the curtain must cover along the planned rod or track. Then read how the seller describes panel width. A number may refer to one panel, the pair together or another stated arrangement. Check the quantity included. Two listings with the same large width figure may therefore provide different amounts of fabric. Consider the fullness you want using the maker's guidance for that heading, rather than applying one multiplier to every curtain style.
Length should be measured from the relevant hanging point to the intended lower edge. Eyelets, hooks and other headings can change where that point sits relative to the top of the fabric. Compare the exact style you plan to use with the hardware already selected. A ready-made length that seems close may still need alteration, so check whether that is practical and include the cost if it forms part of your plan.
Check the complete hanging set
Confirm whether hooks, rings, tiebacks or other components are included or sold separately. Compare the curtain's requirements with the rod or track instructions. A photograph showing a finished window does not establish that all its hardware belongs to the fabric purchase. List the necessary pieces so one apparently inexpensive panel does not become an incomplete installation.
Imagine a hypothetical pair advertised with a combined width. You read the number as the width of each panel and expect more fabric than the order contains. Checking the listing's measurement convention would reveal the difference before delivery. The same care helps avoid ordering a heading that does not work with your existing hardware.
Read the fabric's care instructions before altering or washing it. When the curtains arrive, check dimensions, quantity and heading under the retailer's applicable assessment conditions. Follow the installation guidance and verify the final coverage before making permanent changes. Keep the successful measurements and product details, especially when several windows use similar-looking but differently sized curtains.