I usually cut foam with a slight bevel, making the bottom piece of the foam (the part that sits on the wood) almost exactly the same size and then angling the knife away when I cut to make the top wider all the way around. The angle depends on how thick the foam is. This way, when you pull the Dacron wrap and fabric tight, it smooths the wider top foam edge down over itself a bit and gives a nice rounded profile. Trim the Dacron wrap about an inch from the staples and feather out the edges by pulling away some excess batting layers with your fingers (the good stuff is layered in sheets, like puff pastry, so you can thin it easily). Then staple your fabric a little past the batting so it won't show on the bottom. You can buy professional dust cover material to hide it all for about $2/yrd. It doesn't ravel, so just cut the size you need to cover all the raw edges and staples and attach. You can even color the backs of the staples with black magic marker before you load them in the gun if you really want to hide all evidence!

Thanks equest. I will definitely hide the underside of the dining room chairs when I finish with them.

Brutus, I'm assuming you're doing a slip seat, (no top welt)
I cut my foam exactlty to the chair frame dimensions.
Then on top I use batting, then on top of that I put muslin. Upholstery takes a lot of practice. Slip seats
are a good place to start. Cut one chair first, after you put the foam and dacron on (BTW, I always use dacron on top of the foam) sit on the chair. If it's comfortable and you don't feel the frame sides, then proceed with the fabric. Pay close attention to pulling the fabric as you're
upholstering to get the fabric on even -- I mean not crooked. Are you using a welt on the bottom?
Good luck, Joann

thanks Joann, no I'm not doing a welt. May I ask, what is the purpose of the muslin? Is that to hold things smoother for when you put on the actual upholstery fabric?

The dacron y'all speak of. How is that packaged? Where is the best place to buy?

The batting I used was not the correct stuff on the other chair. LOL Told you, I'm flying blind here.

Thanks for your help.

yes,the muslin holds it together nicely with a smooth finish on the top. The batting you can buy in Wallmart or Joann's fabrics. It's a slip seat then, you know they sell trim with a fabric edge (looks like welting) You can use this on the bottom of the seat --you apply it after put the fabric on, or you can make a welting from the same fabric as the chair.
Remember the antique chair we did for our daughters secretary? That had horse hair in the seat. We of cource left in the horse hair. We made a self welt on the bottom of that chair... Anyhow, I really think a welt on the bottom of the seat makes the chair.
Even if you don't sew,
you can put together the welt (with heavy cording) -- I actually don't use regular welt, I buy cording and sew my fabric around the cording.

This is the chair we did recently. I used heavy cording to make the welting, however, if you don't sew you can put it together by stapeling the fabric wrapped around the cording, to the bottom of the chair...BTW getting a helper is the best way to go when doing upholstery...many fingers make less work! Joann

Thanks Joann, but I misunderstood what a slip cover was. I'm just wrapping fabric around the seat and stapling to the back, that's it. I don't sew and don't own a sewing machine.

I know this stuff comes easy to you but for me it's not so easy. I'm not crafty. I can cook, but sewing escaped me during my formative years. They tried to teach me how to make a skirt in home economics in a half a school year and still I didn't "get" it. I have tried, but never could perfect it so I gave the sewing machine away and pay others do my sewing for me.

I can sew a simple pillow or a curtain, but I find it stressful because it just doesn't come natural to me. I do not have that "crafty" gene.