Welllll... at least the Theia calculator doesn't require getting up off yer arse ;)
This one lets you select sensor size, distance to target, and width of target area, and will provide lens length... it only has 1/4, 1/3 and 1/2 sensors, but for oddball sizes, you can always go one size larger, which will give you a slightly wider FOV for a given lens, then either accept the extra area, or guesstimate the proper lens from there. If nothing else, it will give the minimum focal length you need, and you can go for a varifocal that covers that.
Could try Pelco's as well: Pelco Field of View Camera Lens Calculator - select sensor, then provide two of three factors (FOV, lens length, or distance) and it gives you the third.
JVSG's calculator lets you play with a lot of different parameters, including mounting height, tilt angle, required PPF, etc.