Remember that an undermounted sink will have an inch to an inch and a half of stone above the rim of the sink, so it will be that much "deeper" below your work surface.

https://www.us.kohler.com/us/browse/bathroom-bathroom-sinks/_/N-2562Z2e8aZ1z141tsZ1z11u1g?Nr=P_product_market%3AKPNASite

Maybe you should consider 5" which looks like this below the surface

@tatts - I have no idea why you are frequenting the houzz forums questioning why people are asking questions.

You responded in the same belligerent manner on a thread started by someone having extreme difficulties with regard to electrical work in her NYC coop.

If you feel a thread is a waste of time, do yourself and others a favor and don't read and don't respond. This forum exists for people to seek advice from others who have hands on experience or might have meaningful insight or know of alternatives with better functionality or whatever else people remodeling and decorating their home seek advice on.

You also reveal your ignorance by stating that bathrooms sinks are small as if all bathrooms sinks were the same size and depth which is completely untrue which means you don't even have adequate knowledge on the subject so your posts are doubly meaningless. Obviously bathroom sinks differ quite a bit in both size, shape and depth. Since most people don't buy bathroom sinks that often and don't have the ability to check out every possible sink in person, input is sought on sinks or whatever else people have questions about.

Do yourself and others a favor - don't respond if you add nothing to the dialogue - go read a book or cook a paella or whatever other more meaningful activity you can engage in other than reading posts that seem to annoy you.

My first house had DEEP bathroom sinks, and I didn't appreciate them 'til I moved. The brand was nothing special: I think they were American Standard overmount sinks. I suspect they were inexpensive, but they were so functional.

My current sinks are really pretty but shallow -- I'm going to guess 4" deep -- and I hate them. If you turn the water on with any force, it splashes back at you. We're all in the habit of drizzling the water out, but guests often soak themselves.

I don't see what difference rectangular vs. round/oval would make in the equation, but I do like the look of rectangular sinks.

You can view many sinks by size, depth, shape etc... at faucetdirect.com although I do suggest to purchase locally if you can. This website has many brands all in one place for inspiration. Here's a link for rectangular white sinks priced low to high:
https://www.faucetdirect.com/bathroom-sinks/c55?f21716=undermount&f17776=whites&f17858=rectangular&r=48&s=PRICE_LOW&p=1&categoryid=55

Also, here are a bunch of Houzz stories about bathrooms. The first one is all about bathroom sink size:
https://www.houzz.com/ideabooks/query/rectangular-bathroom-sink

Finally, once you've narrowed down your choices, hire a designer who can help you navigate the nuances for a perfect bathroom.

: ) Rhoda

@Fry - I have visited websites with sinks and do have various sink options saved but I am seeking people with actual experience regarding functionality in terms of whether a relatively "short" rectangular under mount sink is less functional than a deeper sink.

My designer and I both think a rectangular under mount is best in terms of design and the ones I am finding are relatively short in comparison to oval bowls I am used to.

You'll also need to figure out how your faucet interacts with the sink. Good to know you've got a designer on board to help you! : ) Rhoda

Thanks for the advice on the faucets. Mine are somewhat high arced wide spread faucets. Not extremely high but the normal higher for bathroom faucets.

I had wondered whether water on a relatively short sink would create excessive splashing. I don't want to have to think too much about turning on a faucet :-)

We have the Kohler Archer sinks. I love them. Being female I wash "delicate undergarments" out by hand and they are deep enough to do this. Also, deep enough that there is no "splash back." However, when the granite countertop was fabricated, we were charged an additional fee for the tighter sink corners. Not sure if this is standard practice today.

The Kohler Archer seems to have some kind of ledge around the interior - maybe I am misinterpreting the online pictures though.

Maybe it is a perception thing - I have rectangular Kohler undermounts (Verticyl) and they seem fairly deep and I have no issues with splash back or anything; yet when I look at the measurements it gives a height of 6 3/4” but actual “water depth” is 3 1/8”.

Photo from Kohler site:

Hi Helen-

I don't know about the depth.

But I would get as wide and long as you can fit.

Otherwise, when you wash your face you will splash all over the place.

And not too low, so you won't have to bend down too much.

Oh, and about the depth, do you ever rinse anything in the sink?

If so, you'll want a deeper sink.

Helen, I would love to know what you went with in a rectangular sink and if you're happy!

I am having the same questions as you did two years ago, which led me to your post .Thank you!

dsb333 - I went with a rectangular sink - One of the Kohler models with not a particularly deep bowl and no issues at all. I love the way the rectangular under mount sink looks and it doesn't splash at all.

Great to know, thank you so much!!

This was a helpful post as I am having the same dilemma😊. I had a feeling I shouldn’t be so worried about the depth as they more than likely wouldn’t make a sink that people would dislike so much that they wouldn’t buy it.