Curtains fail in two common ways: too narrow, so they look thin and mean when closed, and too short, so they hover awkwardly above the floor. This calculator works out the fabric width you need for proper fullness, how many standard panels that means, and the right finished length for the style you want.
Curtain Calculator
Get the curtain width and length right first time, with no awkward gaps or short hems.
Assumptions: the rod width defaults to the window width plus 8 in on each side, so the curtains can stack back clear of the glass. Length is measured from the rod down to the hem. Floor and puddle lengths need the sill to floor distance, as windows sit at different heights. Ready made panels are sold flat, so the finished width of each panel after gathering is narrower than its flat width.
How it works
- Measure your window and enter its width and height in inches.
- Set the rod width, which is usually the window plus about 8 in on each side so the curtains can stack back.
- Choose your fullness, from a neat 1.5 times to a lush 2.5 times the rod width.
- Pick a length style, sill, apron, floor or puddle, and the calculator gives the panel count and the rod to hem length.
Frequently asked questions
How wide should curtains be compared with the window?
The total flat width of your panels should be at least 1.5 times the rod width, and 2 to 2.5 times looks fuller and more luxurious. Measuring the rod rather than the glass matters, because the rod is wider than the window.
Where should curtains hang in length?
Floor length is the most popular finish, ending about half an inch above the floor so the fabric hangs cleanly. Sill and apron lengths suit kitchens and windows above radiators or furniture.
How high should the rod go?
Mounting the rod about 4 in above the window frame, or closer to the ceiling, makes the window look taller. Whatever height you choose, measure the finished curtain length from the rod, not from the top of the frame.