Believe it or not, this sewing tip is courtesy of Tom Silva, from This Old House. He used this method to space porch pickets, but when I saw it, I thought it would work great for placing buttonholes.
Mark a piece of elastic at regular intervals. (I’m placing my marks 1 1/4″ apart.) When you stretch the elastic, the distance in between the marks will increase, but the marks will always be evenly spaced along the length of elastic.
You can use the sewing machine’s presser foot to hold one end of the elastic, or use a binder clip to attach one end of the elastic to the edge of your table. Now stretch the elastic across your garment, decide on the button spacing that looks best, and mark where you’d like to place the buttonholes.
This was a ready-to-wear skirt that I thought would look nice with a line of off-center decorative buttons down the front. I decided on 8 maroon buttons that picked up the color of the little star-shaped flowers.
There are no rules here, but typically, functional buttons are smaller and closer together on thinner garments like blouses, and you’ll see larger buttons that are placed farther apart on thick garments like coats. Tiny buttons on a chunky wool coat are probably not going to stay fastened, and you will have gaping issues if you use too few buttons on a blouse. Also, if you don’t put a button in between the bust points, you can expect a gap there because the garment will pull the most at the largest part of your chest as you move around.
That advice does not apply to buttons that are purely decorative; they can be whatever you want them to be. And interesting and unexpected button styles or placements can really take a garment to the next level, so don’t be afraid to waltz right out of the box. Test out a bunch of different looks, and go with whatever floats your boat.