distance to echo x 100 x degrees of tilt change from parallel beam = radar top
In order to know the tilt, you need to determine true zero first. The tilt in degrees as indicated on your display or on the tilt knob isn't indicating the true tilt. Also, one needs to know the size of the dish and width of the beam.
Even at that, where the return runs out isn't necessarily the top of the cloud or the storm. Where the cloud ends may be much higher, as may turbulence. The returns will change as the cloud glaciates (turns to ice) and starts to decay.
A good rule of thumb, rather than attempting to climb over, is just to go around. When trying to plan a path across a cell by figuring the tops, you may be surprised if the cell continues to climb. It can continue to build, or additional cells build much faster than you can climb...and it may well be attenuating things building behind it. Best to go around.