4oz of soap will turn into 4oz of soap. You just need to write down exactly how much of what goews into a bar of soap & figure out what it all costs & find a mark-up that is fair. 4x is average I think in this industry.I fill a Pyrex cup with cubes, melt it, (usually gives me 3 cups), and that usually is enough for a 3-4 bar pour
If you buy in bulk (24# BLOCKS) The base costs about $1.30 a pound, add another .70cents per # for shipping, that is $2.00 a pound.
Add a tablespon of fragrance (you need way more fragrance for CP cause a lot of it burms up so to speak from the lye.... or somthin' like that) which is about .30 cents, so that is $2.30 to make a pound of soap.
Divided the pound into (4) bars weighing 4oz ea, that is a cost of .57cents each.
Add a penny for a drop or 2 food coloring, maybe a nickle for a pinch of poppy seeds, etc, it's still very inexpensive.
You need to factor in the cost of your overhead, molds, bowls, scales, etc.
Don't forget packageing like cello bags, ink, labels & ribbon too.
You should factor in your time as well.