edit: I misunderstood the OP; your concern is that the 3cm slab you ordered seems to be slightly less? I'm surprised it's that noticeable when compared to the island! Do you have a picture?

Some will classify a thickness as 2 cm, 3 cm, etc, & may use this as a reference rather than a true measurement. This really should have been a question of your supplier. "What's the finished or true thickness?"

Soapstone being a natural stone like granite, not man-made like quartz, is cut from slabs. Once cut, it's milled to a thickness. This can vary.

To put this in perspective, 2.5 cm = 25 millimetres ( .98") , 3 cm = 30 millimetres (1.18"). The difference is obviously 5 millimetres. That translates to just .197 of an inch or just over 3/16" ( .188 of an inch) difference.

Still, a question for your supplier.

Personally, I think it's acceptable. If we were talking 2 cm to 3 cm, that would be a different story.

There is an acceptable variance in thickness by the MIA. I think the max is about 1/8". I don't know about soapstone as much. Did you see these slabs or tag them before hand? Either way, such a small difference, I personally would let this go.

http://pubs.naturalstoneinstitute.org/pub/eb906eb0-f395-40d1-0381-74e7d2821b3f

I suspect it's like buying a 2x4. It's a name, but not the 'real" size.

"the “thickness” (size) of a 2x4 is listed on a receipt."

It is? A 2x4 measures 1 3/8" x 3 3/8" (both dimensions being ish)....................

millworkman, I thought OP was asking whether slab size should be listed on the purchase order; I wasn't referring to whether the precise measurements should be included (hence quotes), just that the size of the slab ordered should be denoted.

My sales receipt lists the various details of the countertop to be installed, like sq ft, edge, thickness. For the thickness it says 3 cm. My questions is: Is the installed thickness supposed to be 3cm or is it typical it to be within a range of that thickness, or what? Mine is off by ~16%. I threw the 2x4 in there just as an example of something you buy that really isn't what it says it is...another example could be a gallon of gasoline.

When I look at my kitchen with a critical eye, yes, I wish the stone was a bit thicker. But for daily use, no I don't notice because I simply don't have the time for that. Yes, I picked out the slab and it was a typical thickness, not noticeably thinner than other slabs.

I never thought to ask what the final thickness would be. This is the first time I've had to do anything like this (hopefully the only time, lol). I was asking here so I would know what is considered acceptable in case I decide to review the job, or ask about it. Frankly I don't know anyone else who would know about this.