Here's an easy redneck way to figure your combined needed base and ring height.
Put your rifle in a gun vise, vise, or whatever. Make sure it is 'level' across the top of the receiver.( Seriously, use a bubble level)
For a 40mm objective 'lens' scope, start with 'two' stacks of 5 quarters, taped together, put these two stacks of quarters on top of the receiver where the bases are going to bolt up.
Put your scope on top of the quarters and see IF you have enough objective bell clearance. Mind the fore and aft position of the scope, it should be close to where it needs to be for proper eye relief.
If you don't have the 'top of barrel' to 'bottom of objective bell' clearance you need, add a quarter or three, whatever, to your stacks of quarters.
When you have found the right amount of quarters, simply measure the 'stack' of quarters with a dial caliper.
This is the COMBINED base and ring height you need.
( Leave yourself about .125" clearance) from the TOP of the BARREL to the BOTTOM of the scopes OBJECTIVE BELL, this will give you some 'wiggle' room as you probably won't get a ring and base combined height to land exactly on the measurement you found you need from measuring the stack of quarters.
Or you can let the scopes objective bell touch the barrel and just 'add' .125" or whatever you feel you may want as to objective bell clearance, to the measurement of the stack of quarters.
The measurement you get from the above task, is the COMBINED, ring and base height you need.
All ring and base manufactures list the base and ring heights for their products, although you'll have to call some of them on the tele to get these dimensions.
Careful with the 'ring' height measurements as some companies give ring height dimensions from the 'top of the ring mounting base' to the 'center' of the ring, you'll have to subtract .500" for a 1" ring and .591" for a 30mm ring, from the 'total' given ring height to find the ring height dimension from the top of the ring mounting base to the bottom of your scope tube. IF the rings do have their height dimensions given to the center of the ring.
Easy, and all it takes is a 10 minutes and a roll of quarters! lol hehehe
Good luck with it!