I was looking into buying a strapless nursing bra for the summer as I cannot get away with going bra less while nursing. I end up soaking wet.
I measured around my chest. Then I added in my seam allowance for the length around 1″ total because I’d need seam allowance for both ends. For the height of it, I did 7″ or 8″ with the seam allowance added.
I sewed an elastic casing across one whole long side (the one without the opening), then I sewed a casing along the outer piece for the side with the opening. You’ll need to open up (seam rip) one side of the nursing bra to fit your hand through to feed the elastic in- or you can be a normal person and wait to sew that side up- and wait to add the snaps.
I stretched my elastic along the whole casing to decide on the length of the elastic for each casing. Then I cut the elastic and threaded it through (use a safety pin). I sewed down the one end of the elastic, finished bringing elastic through to the other side, sewed that down, removed the elastic.
This is it finished!
Sew the short end closed now (and add snaps if you were smart and waited)