Take a ball of cotton string and measure out enough to double for your header and tie a knot at that point, do not cut yet. Place the knot at the top of the curtain rod and let the ball fall and unroll the string. Decide how much of a puddle effect you lik, and double the puddle amount and then cut the string on the floor, not the knot at the top. Then untie the knot and measure the string and determine the length from that.

Thank you for your reply, I'm going to try it.

I am glad that I could help you . I used to work at a JoAnn Fabric and helped the ladies figure out how much fabric they needed.

Susan,
Here are a couple of things to keep in mind, if the rod is already installed, measure from the top of the rod to the floor; if the rod is not installed yet, when the drapes are done, put them on the rod and hold everything up to the window to determine the proper placement for the brackets (obviously a 2 or 3 person job); if you were asking about how to measure the fabric accurately, getting a square end to start with is your best bet. I use a metal carpenter's t-square that is 48 inches long. Once I have my square end, I use a metal measuring tape to measure down both sides of the fabric, then use the t-square to join the lines. I use a metal measuring tape instead of a fabric one because it won't ever stretch out of shape and size. Hope this helps!

Thanks so much, Trishia. I'm going to save this thread.