Fights take place on an open grid 18 five foot squares wide and 14 five foot square high.
You can pick a custom map which brings its own dimensions. To create a custom your need to login and go to the Maps section.
The goal is to have your five foot squares that the characters and monsters stand on be a reasonable size.
We have always used 42 pixels as a good balance between having enough squares on the web page for the battlefield with still be able to see the character portrait.
If you want to keep that scale (you enter the scale in pixels when you create the map) then you need to look at your map inside an image editor to determine how many pixels are currently representing 5’.
For example I opened this Wyvern Tor map that came from a bundle of assets I purchased from one Patreon artist (https://www.patreon.com/venatusmaps)
In microsoft paint, using view rulers, I can see that each square is 150 pixels in size. That is a little big, so keeping the ratio, I resized the pixel width to be a 1/3 of the size, 50 pixels per square.
Diving the new pixel width by 50 gave me the number of squares height and width and ready to upload to an image site.
Sign in first
Now you can do New Fight and click the settings icon and choose your map.
If you didn’t click Publish then you need to be logged in to see your own map.
Keep in mind some huge monsters are going to get stuck on some of these custom maps