Alexa does both  .. You can use either the integers 1 to 10, or alternatively the percentage values ‘1-Percent’ to ‘100-Percent’… just include ‘percent’ in the syntax when making the adjustment to volume.

Hmm.  That isn't working for me.
Alexa says volume can only be set between 1 and 10  - even when saying percent.

I’m sure Alexa was accepting numbers between 1 and 100 (without saying percent) about a week ago.  

Thank you for the suggestion though - I hadn’t tried that previously!

Edit - I also read on another forum that you could say something like increase volume by 10%.  But Sonos then goes to 100%!

I’m not near my system at the minute, but perhaps Amazon have changed this then?
I mostly use the 1 to 10 integer control myself, as I have in the past asked for 10 percent and it’s jumped to full volume. So maybe that’s their reason for changing this?

I’ll be home shortly, so I will see if it’s the same for me and report back.

Okay it seems you’re correct - I just got home and tried this on a Roam, saying:

“Alexa, set the volume to 1%”

…and whilst the volume slider moved, it actually shifted to 10% and when I asked for 25% Alexa replied, “Sorry you can only set a volume between zero and ten” - so it appears I was wrong, or this has changed at some point. 

I’m personally okay with that, as the integer adjustment is simple and what I normally use anyway, but just slightly prohibitive for those that may want more control. I guess there’s always the App, if that’s perhaps required.

I’m just testing now to see if volumes of 1.5, 2.5, 3.5 etc; will work aswell?

Well it looks like it’s 1, 2, 3 etc. whole numbers only. I guess that’s the way it’s going to be then, going forward.‍♂️ 

Thank you for checking.
The only other suggestion I saw was to change the volume limit in the Sonos app.  We already have a volume limit set of 75%, 

A bit more control would be useful.  Even to allow halves.  

Looks like this was suggested as a feature some 3 years ago.  So, we might be waiting a while!