The Ruler tool lets you click and drag to measure distances on the table. While you measure, you can choose to show your measurement line with other players so you can discuss what you're measuring, or you can limit the measurement line visibility to just yourself and your GM.
Changing Settings (GM only)
The grid settings and default Ruler behavior can be changed in the Game Default Settings, or each page of the campaign can have unique settings, changed in Page Settings (accessible via the Page Toolbar)
You can change ruler and grid settings for each page by accessing its Page Settings. Among other things, you can change the scale, the distance units (feet, meters, etc.), and how measurements are calculated.
There are two grid types, Square (default) and Hex, and the grid can be disabled. Your choice of Grid changes the options you have. Hex Grids have the option to show the grid label in each space.
Square Grids have four options for measuring:
1. D&D 5E/4E Compatible is the default setting. This measures a diagonal move as 1 unit. This simplifies the counting of squares at the expense of realism.
2. Pathfinder/3.5E Compatible measures a diagonal move as 1.5 units (rounding down). Thus, when 1 unit equals 5ft, diagonal moves alternate between 5ft and 10ft increments (i.e. 5ft, 15ft, 20ft, 30ft, etc.). This is slightly more complicated to count, but models reality more closely.
3. Manhattan measures a diagonal distance as the sum of its horizontal and vertical distances. Effectively, a diagonal move equals 2 units using this method. This is also called "Taxicab geometry" or "rectilinear distance".
4. Euclidean measures diagonals using the Pythagorean Theorem. A diagonal move equals about 1.414 units using this method. This is also called the "real distance" or "as the crow flies."
Hex Grids have two options for measuring:
1. Hex Path measures a diagonal via the shortest path to the destination, adding one unit for each hex a token would have to pass through to reach the end point.
2. Euclidean measures diagonals using the Pythagorean Theorem. A diagonal move equals about 1.414 units using this method. This is also called the "real distance" or "as the crow flies."