Calculator + chartEnter your measurements below and it works the answer out.
You need three measurements: window width, window height, and the height from the floor to the top of the frame. Take them in inches with a metal tape, enter them below, and the calculator turns them into the rod length, panel width and curtain length you order.
| Measurement | From | To | Why it matters |
|---|---|---|---|
| A — Width | Outside edge of the frame, left | Outside edge, right | Sets the rod length: the rod runs 6 in past each side so the open curtains clear the glass |
| B — Height | Top outside edge of the frame | Sill (bottom of the frame) | Sets sill-length and below-sill curtains |
| C — Floor to frame | Floor | Top outside edge of the frame | Sets floor-length curtains: the rod goes 5 in above this point |
Measure width in three places (top, middle, bottom) and use the widest; old frames are rarely square.
Rod length is the frame width plus 6 inches each side. Curtains stack back onto the wall when open, so the rod has to be wider than the glass or the panels always cover part of the window.
Rod height is the floor-to-frame measurement plus 5 inches. Hanging the rod above the frame makes the window look taller; 4 to 6 inches is the usual range and 5 is the calculator's figure.
Panel width is the rod length multiplied by the fullness ratio (1.5×, 2× or 2.5×), split into an even number of ready-made panels so the pair parts in the middle.
Curtain length runs from the rod down to the point you chose — sill, below sill, floating, breaking or puddling — and is rounded to the nearest retail length (63, 84, 96, 108, 120 in).
The outside of the frame, for all three measurements. Curtains hang outside the frame, and the rod brackets go on the wall beside it, so the glass size is not what you need.
4 to 10 inches each side; the calculator uses 6. More extension lets the open curtains clear the glass completely and makes the window look wider.
4 to 6 inches above the top of the frame on a standard wall. On a high ceiling, halfway between the frame and the ceiling reads best; the calculator uses 5 inches.
Go longer and hem, or accept a slight break on the floor. A curtain that is too short is the one mistake people notice.