Context is key. Post up a pic or two as not everyone can get a good mental picture.

I got rid of a sill in a kitchen wndow and I dont miss it. I wasnt sure....they did picture frame trim out and no more marblelite sill.....I had to think about it for a bit. How many inches are you talking about? i wouldnt do too much. You can use a 3 in sill for a couple of pieces of ceramics if you want.....do you want a window sill for herbs and more in pots ??..then do more but if thats not your thing /or counter is available along the span of window for a plant or two.......I'd keep it back at more the minimum.

I did no sill w trim out /like first 2 shown...... others shown w sill..

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This is how it is right now. The sill is 3cm quartz. Backsplash 3/4 running underneath the window sill.

I would do a 4 inch sill, if, if possible. I really dislike skimpy window sills in a kitchen. I have a 3 inch one in my kitchen, and have thought of changing it to 4.

That wall had to be built out for plumbing, so the sill is around 6-7 inches deep without overhang. We are wondering how much extra overhang past the backsplash. The countertops are 2in deeper than standard, so getting too close to the faucet is not an issue. Is just aesthetics/proportions. We are thinking either 1/2 or 3/4 past the backsplash, not sure. Again the sill is 3cm thick quartz.

That looks like a very wide sill - what will the finished top surface measurement be? Regardless, for a sill that wide I think I would want a minimum overhang past the backsplash. The extra width doesn’t seem to be needed for placing items on the sill.

ETA: my post crossed with yours - 6-7” is a generous sill. I’d still do minimal overhang for it. If you know that you’ll place items on the sill & know what those items are, then go wide enough to accomodate.

the whole window is recessed..... I would treat the four recessed sides the same..and use backsplash tile/maybe tile up to ceiling ...... Its a whole integrated look with the recess that you want to look good......you dont need any extra sill......but you have to deal with the returns on all 4 sides. I'm hoping the reach to operate the windows is working for you. they call this a "deep boxed window"...yours is even deeper. they cased out all the returns.....tile would be fine w yours...but something......

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Thank you - yes the sill is wide, so it is not for functionality, just for aesthetics. What is the minimum overhang? Forgot to mention that the sill will have "dog ears" at both sides to meet the casing.

You may also want to confirm the sill overhang won't impede the faucet handle or use of your faucet (or any other sink accessories).

The countertop is 2in deeper than standard, so that is not an issue.