As I think more about it, I think just doing the 30" vanity and keeping the 36" shower would be best anyways since I'd like to put a folding bench inside the shower which even folded will take up a couple inches of space.

I don't really understand the 24" from tub to toilet in that last picture though. For us, code only requires 15" from midpoint of toilet to both vanity and shower, so we'd be looking at 30" of total space required for the toilet.

You are right the standard allowance is 15” from center of toilet. IMO a larger shower than 36” is a must even without a bench and I like removeable benches that fold up . Could you please post a to scale detailed drawing of the space making sure to mark doorways .

The last is about clear walkway spaces required. It’s 24” of clear space to step in and out of the tub that is required. These dimensions will all be checked for compliance when your project has its’s required design documents permitted. And again during the inspection process.

5x8 is very small for a master. It’s hall bath tub/shower combo sized. I would look at the home design as a whole to see if something can be altered to create something more spacious.

My husband is an Engineer and he's working on the CAD drawings, so I don't have them yet, just all the dimensions. He was the one who told me we can only do a 30" vanity max, but of course I don't listen and now I have to tell him he was right lol.

My first thought: That's a HUGE bathroom vanity! It's the size of a kitchen island! Why would anyone want such a wide vanity?

My more realistic thoughts:

8x5 bathrooms kinda fall into place by themselves ... they just work in this layout:

You don't need 24-30" clearance across the entire tub ... you just need that space at one end so you can enter the tub (or shower, if that's the way you want to go). You do need the 15" from the centerline of the toilet.

30-36" is not a decent-sized vanity ... master bath or not. You won't have any storage space at all. Can you steal some space from the bedroom? Without having seen your space /just speaking in general terms, I'd rather have a small bedroom and a more comfortable-sized bathroom.

Mrs. Pete's plan is a good one, the one I think feels the most spacious, although I personally prefer switching the sink and toilet. I know that there is always an outcry here about toilet visible through door, but I do think it's more practical to put the sink in the middle for these reasons:

1. It's a 5 x 8. They're going to see the toilet anyway.

2. The door swing is waste space. Use that for standing room in front of the toilet. (ETA=Oops. In new construction this is moot. I'm used to older baths this size. Today you wouldn't put an in-swinging door on a barh for safety reasons.)

3. The sink/vanity is shallower than the toilet. Putting it next to the tub gives you more space for getting in and out of the tub, and you can use the wall opposite for towel bars, train rack, whatever.

Having said all that, I have a 5x 8 where the tub is on one short wall and the sink and toilet on the other with the door in the middle of the long wall and that's not hateful, either, although given my druthers I'd prefer the railroaded layout.

A 36" vanity is too big for either layout, though.

ETA Found a pic of the layout I have:

Our master is 5 x 11 and the same layout as Mrs. Pete's drawing. Our shower is 34" wide and it's never felt cramped. The toilet has 36" and I would not go to 30", especially if your shower valve is on the toilet wall. If so it can be moved to the opposite wall if it's not an outside wall in a cold climate. That leaves you less than 30" for a vanity. If using that small of a vanity, I'd do an all-drawer vanity with a recessed mirrored medicine cabinet. It doesn't give you much counter space though.

That's very surprising that this is a master bath. It's small for even a hall bath these days. It's tiny for a 2020 master.

Hey, I would love to have an 8 x 5 master bath! I have only ever lived in one place with a master bath.

You do have the in-between options. Look online and you will find 32," 33/" and 34" vanities. You can make the shower 32" or 34". Definitely get the deepest medicine cabinet you can afford. Even a 4" deep one will hold a lot. If you get one with an electrical plug inside, you can put the toothbrush and/or the electric razor inside and not have them sitting out.

Don't forget that 30 x 60 is the standard size for a replacement shower when getting rid of a tub.