Here's the thing about store-bought curtains....most are NOT EVEN. Not remotely close to being even. Why is this a problem? If you rely on the seams and folds, your hemming will be off and your curtains will be uneven!
Here's the problem. It seems logical to measure from the top of the curtain to the floor. We take that measurement and add about 4" for the hem. What you'll end up with are some curtains that don't hang straight; the panels don't line up with each other.
Why? The curtains don't hang from the top. Most have grommets or a casing that the rod slides into. And that's the issue. Store-bought curtains, from my experience, have uneven hems or misplaced grommets. AND...the curtains rest on the rod at the casing or grommet top.
I have been helping a friend settle into his new house. He purchased two curtain panels for his daughter's bedroom - she's got two windows: one wider than the other. There's a weird ledge, so they needed to be shortened - to almost half the length. His idea was that I could (1) shorten the two panels for the bigger window and (2) use the excess fabric to make another panel for the other window... Sure. We'll get to that in another post.
So we hung the curtains on the rod and I measured; I placed a pin at the appropriate length. I took the curtains home and laid them out on my table and measured:
But I didn't do this. Why? when I stacked the grommets on top of each other, they didn't line up. Some were closer to the top than others.
SO DON'T DO THIS or you'll have uneven curtains. Mine were up to a 1/2" off!!
DO THIS! The curtains hang on the rod from the top of the grommet (or the top hem in the casing). So I measured from the top of the grommet to my pin (the correct length) and got 40".
I added 4" for the bottom hem (40" + 4" = 44")
Using my tape measure, I measured 40" and 44" from the top of the grommet opening and marked with a pen.
I went to my cutting table and cut off the excess fabric at the 44" mark. OH...this fabric was a pain to work with! It shifted all over the place...thank heaven for painter's tape!
I pressed at 40" and tucked 1" under for a seam allowance.
I measured again. I held them up and looked. Were they even? Yes! I sewed the hem using my walking foot and a 4mm stitch length.
They turned out great.