@rhiorhino I can’t format an answer the way I want on mobile, so I’m doing it like this!

Okay so, it depends! BUT the good news is I do it myself, so I know the numbers really well, but do ask your stylist to double check, some gradients are numbered differently on different brands/places/moon phases

I usually have fluff on top, which I do with scissors. I like having several inches up there, but if you’re looking for shorter, I recommend one (razor number 8, for me) or two inches (less common, but some stylists will have razors for 2 inches, otherwise they can use scissors). The key is to be able to go shorter on the sides, unless you really want to go for full shave.

For the back and sides, I have two styles I go between. Right now (though I haven’t posted recent enough photos, so it’s probably not what you mean) I have 1/8 inch (razor 1) all over. It’s a full undercut look, pardon the wet hair in the pic:

The other look I go for is tapered sides, usually starting at ½ inch (4) fading to 1/8 or ¼ (1 or 2) at the bottom. The taper both looks good to me and helps my hair not look like a mullet so fast (I swear the bottom grows faster than the rest). I don’t have a great photo to show just how it looks, this is the closest:

That’s probably grown out a bit from the ½ inch (and it’s messy, but ah well), but that’s around what it looks like. You can always ask for ¾ inch (6) to start to test it out if you’re worried about going too short too quick (if the stylist is unwilling to work with you, they are a bad stylist. Same with if they give you grief over going short.