trying to determine how much elastic is needed
 

I need to replace the elastic on my fitted sheets. I have king size and twin size that need new elastic. How do I determine how long to cut the elastic before attaching it to the edge of the sheet? Do I cut it the exact measurement of the area that it will be sewed onto.....do I add some inches....do I reduce the length? Thanks for any help in this.

You need to cut shorter--prob by a third, and stretch it as you sew to make it fit the area.

Measure the perimeter of the mattress the sheet goes over, stretch the elastic as you sew it on.
I think I cut mine about 5” shorter than the mattress perimeter when I made crib sheets. I made sure the sheets would fold under the mattress and stay snug.

sounds like a lot of trouble. I would just buy new sheets.

I just did this, and I went with 1/3 less as posted above.

I would, too! :D

I have the elastic strips with "garter" clips on each end. It is best to take them off when washing but they really hold the sheets tight.

Thanks for all your input. I'll give it a try with reducing the length by 1/3.
It does sound like a lot of work but California King sheets are expensive and I inherited a big bunch of sheets from hubby's aunt that are really nice but the elastic is shot---so I'll give it a try---what have I got to lose except a little time---I'll learn something in the process and maybe have some nice fancy sheets.