Check this rim-width-tire-size chart to find the perfect rim and tire match. For Light Bicycle mountain, road, and fatbike carbon rim wheels. More tire choosing guides included.
if you mean the erd, (so you can get the right length spokes, etc) that is specific to each rim. if it's not provided by the rim manufacturer, you'd have to measure it; there are a number of ways to do that:
I ride in deep loose stuff from gravel washes to sugar sand... just doesn't work with 2" tires at 65psi (I'm typically closer to 10psi)... on soft terrain the rolling resistance is not any worse (and at times likely better) on the wide tires. And the good wide tires still handle quite well on hard surface at those low pressures...
Different missions require different equipment. I wouldn't expect a tour de france guy to run 4+" at 8-10psi nor to benefit from full suspension...oh well..