Nut width on a 4 string?

How big are your hands? I have small hands and prefer a 1.5" width but have little issue with 1.62. Can not deal with 1.75"very well. If your hands are larger you might prefer 1.68". If you come from mostly playing guitar you are likely to want 1.5" or similar.

I prefer 1 1/2".

Pre 1962, I'm not sure. From 1962 on Fender standardized and offered four nut widths on all instruments, labelled A thru D

A = 1 1/2" (38.1 mm)
B = 1 5/8" (41.3 mm)
C = 1 3/4" (44.5 mm)
D = 1 7/8"  (47.6 mm) 

Is far as I can tell, unless a dealer specified something specific for an order, Jazz basses were by default an A width (although some people will say it was actually a smaller 1-7/16" width until well into the 70s), Precisions were C, until about 1968 when they changed to a B width. Most Fender guitars were B too. But they were all hand shaped and sanded back then and tolerances were large and they could vary quite a bit above or below those measurements. Player preference varies as widely as the individual measurements!

1-11/16" is regarded as standard Gibson electric guitar nut width (though it wasn't always, it was 1-9/16" from '65 to '78-ish) which Fender started offering on guitars some time in the 90s?

And the constant changing of measurement units between fractional inches, decimal inches, and millimeters (with varying numbers of decimal places and/or accuracy of conversion) just adds to the mess.

Most people seem to prefer the 1 1/2". If you're a die hard P-bass fan you'll want it wider - likely has an impact on tone, as well. I never really notice much of a difference. You're asking for wrist problems if you're a thumb wrapper on a bass anyway, so ergonomically they're pretty close for me. I don't think people who dislike the P-neck do so because they feel it is too chunky (realistically that isn't all that big), but the strings probably feel oddly far apart to them. That is just a guess, though.

Strings crowding together is sometimes an issue with 5 and 6 string basses for people who like to slap and pop, because they want to be able to get in between those strings. It starts to feel like a guitar to them. I don't think a 4-string bass is ever going to be crowded enough for that to be an issue. P and J basses have the same bridge width, so the right hand is going to feel pretty darn close.

Preface: I don't have small hands, but I'm old and both thumbs are arthritic, so this affects my preferences.  I don't slap or play with a pick: just finger style.

I prefer 1-1/2". I don't have a J bass but the nuts on my Guild Starfires and Fender Mustang (all short scale) are all 1-1/2". I don't want thin (front-to-back) just narrow (side-to-side). I also have a Reverend Dub King (also SS) which has a 1-5/8" nut. I like the sounds it can produce, but don't find it as comfortable to play as the others. For me, the Guild neck carve is perfect.  Added note: the string spacing at the Guild bridge saddles is 17mm (as opposed to a Jazz, which is closer to 19mm)

If I was going to buy a Fender P for the sound, I'd get one with a J neck (1-1/2" nut) for ergonomics.

Fortunately for me I'll be ordering from Warmoth. Getting the specs won't be a problem and the price will be around $250.00. I consider that decent for filling my need with exactly what I want.

I'll be ordering a paddle head and cutting my own design for my project.

It continues to appear that 1 1/2" at the nut is the ticket.

I find 1-1/2 to be a little small feeling for me. It's not the string spacing itself. I have a couple of 5-strings with similar string-to-string spacing. I just like a more hefty neck in my hand. "Baseball bat" necks are fine with me. To me, I find the front-to-back dimension more important than the neck width. Then again, I don't play "solo" bass or need a fast neck.

From a guitarist’s perspective 1.5” seems narrow. Considering there are only 4 strings it’s not.

I’ve got both a J and a P clone - with the traditional nut widths. Both are fine with me. I also have the Arthur in my thumbs. I don’t know what the future holds regarding this topic.

For guitar I’m largely 1 11/16” with a couple 1 3/4” mixed in.

I have a Strat build with a 1 5/8” nut, but the 7.25” radius seems to make that comfortable. That’s my theory any ways.

Rick, thanks for the input.

More confirmation of the 1 1/2" width at the nut.

I think I'm settled on that.

Now to decide if I dare go with the slim neck profile.

I have different basses with different necks , if you spend the time you become adjusted.
It really doesn’t matter much now.