I am hoping you bought another top mounted sink. If no one has told you, while you can trade an undermount for a top mount the reverse isn't true. This is true for a couple of reasons.

Under-mounted sinks do not always have holes for faucets while top mounted sinks generally do. That means a top mounted sink is generally MUCH smaller from front to back. So, to replace a top mounted sink with an undermounted one would leave a empty strip where the faucets USED TO BE.

The granite guys don't normally finish the edges of the sink cut out AND they can leave the cut out very rough. If the blanco were a little larger that the cut out, you could try to have the granite guys come back, tidy up the edge and polish it BEFORE you install the sink.

If it is the top mounted version, take the blanco out of the box. There should be a template in there or stamped on the box. It should show the cutout and the actual top edge of the sink rim. Lay the cutout on top of the kohler - carefully aligning the two front corners of the template sink rim to your actual sink. Tape down gently - remembering you might need to remove the template completely intact.

On one side, match the rear corner of the template rim to your Kohler - it should be the same. Unless the Blanco uses some arcane clip system, you should be ok if the BOWL is a little smaller, but not if the rim is materially different.

Thanks. The Blanco sink I bought can be either a top mount or an undermount. There is a template in the box, but the template for the top mount isn't the size of either the entire sink or the bowl - it's the size of the hole that needs to be made in the counter to accommodate the sink as a topmount, so it's somewhat in between the 2.

I did lie that template on top of the blanco sink and try to trace the actual sink edge around it, and then tried to lay that on my current Kohler sink. I can't get it all the way on there because of the faucet. It looks to be about the same (really pretty close) to my current sink, but because my current sink has a kind of a lip on it and because I'm not exactly sure where the granite ends under the sink, I don't know for sure whether the blanco sink will or won't fit. However, I don't think it's obvious that it won't work, which is what the plumber said. I suspect there's not going to be any way to tell for sure unless I have the plumber come back and take out the old sink and see if the new one fits.

But I think I probably should have another sink too, in case it doesn't fit, so I can have him install that one if the blanco doesn't fit. Anyone have any suggestions for another sink to consider?

mamatoalex, I don't have other sink suggestions, sorry, but you could go to the Kohler and Blanco web sites and look up the spec sheets for both sinks. These will give you many exact measurements so you could compare the dimensions of each sink. (Kohler had the specs for my current sink that they discontinued twenty years ago, so they had pretty darn good records! Blanco I don't have any experience with, sorry, but I would sure think they'd have online specs too).

Or, with aLOT of backbreaking upside down work, you could take out everything from underneath your sink, get a couple bright flashlights and a measuring tape--maybe even a cloth one to fit up tight--and shinny under your current sink and measure the cutout. Or at least take a good look to get more info without taking out your sink or paying a plumber anything (well, don't bang into the sink drains too much! ;) ).

HTH, cheers

You might be able to transfer the template to regular paper. Tape some paper together, trace the sink, cut out the part that goes around the faucet/sprayer, etc. before you lay it down.

If it looks ok, then have your plumber pull the sink and try the new one. If it fits, go ahead. If it doesn't, then carefully measure the opening and have the plumber put your old sink back.