Recommended Floating Dock Slip Width

19' which will give you enough room to put fenders on both sides, but the wider the better.

Indeed 19 is minimum unless the slip is exposed or cross current. In this case you may want more...

Really all depends on the weather and tidal conditions of the marina. I use a slip somewhere that is perhaps 20+ feet wide with an 18.6 beam. Waters are dead still and tidal current is nominal in terms of impact. It's also well protected from winds in passing storms. I deflate my fenders to use them on each side.

Fendering can be installed on the dock and would only intrude 2" on each side. So depending on how good a boat handler you are you can get by with less than 17'.

What are you going to do with the extra 1 1/2'. Seriously all you need do is get one corner in and you're home. They sell wheels that you can install on the corners to make it easier for you. https://www.westmarine.com/buy/tayl...ble-dock-wheels--P005_157_006_507?recordNum=1

I found when the boat leaned hard against the wheels, the wheels would often stick and not turn. Result being dirty streaks down the hull and sometimes a little wheel plastic on the gel coat.

Ended up with three small poly balls per side in the slip. Bow, middle and near the stern on the sides. Two more on the dock behind the boat. If current / wind is strong we wet down the poly balls with the wash down as we back in to lower friction in case I mess up and we lean hard on them.

I hate when people refer to "bumpers". They're "fenders", meant to fend off not to bump like a "bumper" on a car. I've seen these wheels get bumped off leaving a beautiful metal corner to gouge fiberglass. They're there to guide you in.

My beam is 15’ 10”. That’s at gunnel height 2/3 to 3/4 of the way forward. At the waterline about 13’ 3/4 forward and a few inches over 12’ at the stern, I don’t recall exactly. My slip is 16’ wide.

Finger docks on either side are only attached at the main dock. No pilings on either side to hit with the rub rail or to steady the fingers.

I would never select a tight slip unless absolutely no other choice. I wouldn't squeeze into 18' if there was a possible 20'. My reasoning is that while anything can be done one time or a few times, it can become a major irritant if you're in and out of the slip on a regular basis and especially when wind and current are misbehaving or when the area is exceptionally crowded with other boats.

It’s the place you want to be? Is the slip available now? How far away is your boat? Why not take it there and try it on for size?
I’ve seen situations where the numbers looked very close but in reality there was no issues at all.

If it's your permanent slip and you can put those rubber wheels on the outside corners and permanent fenders on the dock all of the way in you would be ok once you get 10' of the stern in and start backing in. Not fun in all conditions, but do-able.

Actually all you need get in is a few inches of one corner. Big mistake too many make is when they get that one corner in, their bow blows toward their neighbor, they panic and pull back out rather than just reversing the up-current side followed bumping forward with the down-current side. Result is their whole boat goes to their neighbor. With a twin screw boat once your corner is in you're in.

This. Your beam at your water line is typically less than the widest section of your boat at the cap rail. The really big question is tidal and wind conditions coupled with your confidence in maneuvering your own vessel. As has been posted, getting one corner of your stern clear is as good as being home, especially if you're twin engine, and a thruster makes it a no brainer. But visit your favorite place a few times on the tide clock and watch the behavior of other boats and the signs of current. Understand what you're going to be contending with on most occasion.

As I said, I'm in a slip for a season each year that I wouldn't be in if the tide or wind was much of a concern, but they aren't big factors, and I literally have less than one foot on each side. Once I'm in I deflate me fenders and use them partially inflated to fend the boat in my absence. I don't have a corner roller to use, but I would employ one if the tide movement brought challenges.

+1
And practice, practice, practice.

When I taught my ideal situation was on our south shore barrier islands during the week when there'd be plenty of empty slips. I'd drill my students going in one slip then flip around and go in the opposite slip so they'd get the wind / current on both sides. Worked with one fellow about April. He did good. Got a call from him after July 4th for another lesson. Said when he went to Fire Is. he hit everyone. I asked when he had the boat out last before this. Not since our lesson. I explained that he could hire me every time he takes his boat out $$$$ or he can practice.