JR is right that test fitting at a gun shop is ideal because different scope rings and bases means way different fit by maker. I have always kept a variety of rings on hand to facilitate fitting scopes to guns. That said, if you know which rings and bases you want to use, all of the makers post the height of their bases and the height of their low, medium and High bases. It is pretty simple to add them up to calculate what combo you need.
Here is an example of the Chart from Weaver. Click on hte link it will download a PDF. They all make them.
https://www.weaveroptics.com/on/dema...ountsChart.pdf