By "Watt power" we basically mean radiant flux, and by "stops" we mean luminous flux. These two have similar definitions, but they are different.

In normal life, it is true that if you halve the "Watt power" and that light is reflected from or refracted through linear (normal, not non-linear optical) materials, then your camera will observe half the luminous flux - therefore if you halve the "Watt power", you create the same effect as if you stopped down your camera 1 stops (by changing aperture or shutter speed).

If you use a digital camera, your life is easy. Since you are using a studio strobe, your shutter is fixed, you are smart so your ISO is fixed ;-), and also your aperture is arbitrarily fixed. So make a test shot, see your histogram. It maybe shows you are off 2.5 stops. So just multiply the wattage power by 2^2.5. You will have a great setup with a few trial-errors, and will quickly learn to be intuitive with the controls.