What base size should I use in 40K?

A nice thing to point out is that so long as you discuss things with the opponents that you play with, you can usually use any base size you want in 40k. Unless you’re in a competitive tournament environment, base sizes don’t matter much, assuming you are reasonable with it, i.e., don’t go putting an Ork boy on a Primarch base.

Is there a reference guide for Warhammer 40k base sizes?

So, while there is no official Games Workshop reference guide for tournaments, this guide covers all the current Warhammer 40k base sizes that come inside the most recent model kits purchased new from Games Workshop by faction and model name. Click Here to Get GW Beveled Bases For Less!

How tall is a Dreadnought in 40K?

Actually, comparing codex to imperial armor the average human in 40k is 4 feet tall. Dreadnoughts are 3x the height of a man and they're 12.5 feet. The Sister of battle with her Battle armor on should be taller than the Guardsman, without it on the other side not so much