Just posted this in another thread. Hope it helps:
Quick rundown on LR attys... You can achieve the same results by boosting voltage or lowering the resistance of the atty. Square the voltage and divide by resistance to get your wattage, and this is the number to use to compare apples to apples. For example:
A 3.7 V battery with a 3.0 ohm atomizer: (3.7 x 3.7) / 3.0 = 4.56 Watts
3.7 V with 1.5 ohm atomizer: (3.7 x 3.7) / 1.5 = 9.13 Watts
5.0 V with 3.0 ohm atomizer: (5.0 x 5.0) / 3.0 = 8.33 Watts
It does get more complicated with multiple coils. You end up with a more complicated equation. You add up 1/r (if resistance is 4, 1/4) for the number of resistors (coils), and then invert the resulting fraction. For example for a dual coil, 3 ohm atomizer, you'd get 1/3 + 1/3 = 2/3, and inverted 3/2 = 1.5 ohms. HOWEVER, I think they rate them for the total resistance, so if a dual coil atomizer is rated at 1.5 ohms, then it's two 3.0 ohm coils with an overall circuit resistance of 1.5 ohms... Confused yet?
I often use a variable voltage mod with lr attys, I just turn them down. VV allows me to buy whatever attys are cheapest...