D&D 5E 2.5 ft grid spaces - crazy idea?

[Yaarel]

How would this work with all the different things that add to a creature's move speed, creatures that get up from prone, etc.?

Using zones to ballpark moves uses theater of the mind for gridded-move minutia.

For me, things are either 1) adjacent, 2) within the zone, 3) in the adjacent zone within a move or throw, or 4) beyond at range.

Since getting up from prone, denies a full 30-ish foot move, then you might want to allow movement anywhere in the zone, but not into the next zone. But after a while, you can eyeball distances with minimal disagreements.

The only disagreement I ever had, was adjudicating whether a flying target (diagonal horizontally and diagonally again vertically) was within range. I went by rough approximation by which horizontal zone the target was above, and the other decided to use a string (altho we never used it before). Really we were both right, it just depended on how much the string use was worth.

 

[Ummdustry]

Very late to the party, but I have some things to add:

1. This lets you have a "more reasonable" large size. Currently large creatures occupy 10ftx10ft, and medium ones 5ftx5ft, this means the area difference is A FACTOR OF FOUR. With a creature 7.5ftx7.5ft, you have a more managable steps of 2.25x & 1.77x. It could be a good option for minotaurs, firbolgs etc... when you want "real big boy" but not "can't go inside the tavern"
2. I feel like most of the time you can probably ignore this, If you mark out a 5ftx5ft grid as "bold" and then the 2.5ft by 2.5ft grid as "thin" your players might just opt to use only the 5ft by 5ft most of time. Different colours could also be used (like this). That way there's very little extra book keeping when moving about. You simply count out most of your movement as normal, and then do a half-step if you have to at the end.
3. Reach, how does it work? Seems like a complicated question. Does 5ft reach let a medium creature stab over a 2.5ft gap into a medium creature, or do they still need to adjacent? We could add a new reach catagories perhaps? short weapons (i.e. knives) that need true adjacency, 2.5ft gap (i.e. swords) 5ft gaps, 7.5ft gaps (spears). A lot of book-keeping, but some wargaming tables might like that.
4. There are now more options for tight vs loose formations. Again, somewargaming tables would like that, but I get the impression most tables would just ignore it, or get confused.
5. AoE attacks, do you bother counting out the sub-squares for a fireball?

This here is my attempt to illustrate the range question. Each green 2x2 square is a unique distance away from the red figure (presumable representing the player.) Most are trivial, and it often wouldn't even need to come up, but at some point it will be annoying.

 

[Oofta]

I play using hexes because it simplifies movement. No more counting every other diagonal as two and so on. But that does mean that at times when indoors things don't line up quite right and there are half-hexes cut off or a door that it would seem like you couldn't get more than one person adjacent to it.

So I just ignore the grid when it gets too much in the way. It's there as a reference for movement and telling us range. The grid doesn't exist in the world of the PCs, it's just there for our convenience so at the smallest scales I go a bit ToTM.

I did the same thing when I used traditional 5 foot squares, I just described the situation and went from there and it all worked just fine. YMMV of course.

 

[Lanefan]

Preface: this is an idea for playing on Roll20, where the mapping and miniatures are easily adjusted in size.

So, I was thinking the other day about a dungeon adventure, and I needed to put a door on a map in such a way that it didn't line up with the grid. I was considering the ramifications of this, should combat occur, when I thought: why not set the grid to 2.5 ft instead of 5 ft? I began thinking more and more about it, and while it seems a bit crazy, I'm interested in the idea.

Pros: It would allow more refined movement, especially for slower characters (25 ft speed) when dealing with difficult terrain or standing up from prone. Tiny creatures would have their own space, rather than 4 to a square.

Cons: Needing to Zoom out to see the map better (not a huge disadvantage, since most of us do this normally). Needing to count additional spaces for movement (slowing the game down?). Do creatures need to be adjacent, or within 2.5 ft to melee attack?

Is there anything else I didn't consider? Is this something that is a worthwhile idea, or not really worth the effort?

One thing to consider is that if you or any of your players are using older tech, adding more squares to the map makes it render slower and might (as it did for me) cause roll20 to freeze or not load the map at all.

So, my advice would be if you're going to 2.5-foot squares, chop up your maps such that you've got roughly the same number of actual squares per map as before.

Also, as a player I shut off any and all snap-to-grid functions; and would do so as a DM as well.