Gather a metal tape measure, pen, and paper
Decide where the curtain rod or track will be installed
Measure the width of the window or the full area to be covered
Add extra width on both sides if you want the curtains to stack clear of the window
Measure the height from the top of the rod or track position to the desired curtain length
Choose the length style you want: sill, below sill, floor length, or puddled
Measure at least three points for width and height to account for uneven walls or floors
Record the smallest height if the floor is uneven
For inside mount curtains, measure the exact inside width and height of the window frame
For outside mount curtains, measure beyond the frame for full coverage
Measure each window separately if they are not identical
Double-check all measurements before ordering or cutting fabric