Ohm's Law is a fundamental principle in electrical engineering that describes the relationship between current (I), voltage (V), and resistance (R).
The basic formula for Ohm's law is: V=RxI

(V) represents the voltage across the conductor.
(I) denotes the current flowing through the conductor.
(R) is the resistance provided by the conductor to the flow of current.

Ohm's Law Formulas

I=V/R For Mech Mods

I=P/V For Regulated Mods

I=√P/R For Regulated Mods

P=VxI For calculating mech mod's power loss

P=V²/R For max wattage for given resistance, due to voltage limit of device

P=I²xR For power loss at mech mods

V=RxI For voltage sag of battery - For calculating mech mod's body voltage drop

V=P/I For Regulated Mods

V=√PxR For Regulated Mods

R=P/I² Lower resistance required to reach max wattage due to current limit of device

R=V²/P Higher resistance required to reach max wattage due to voltage limit of device

R=V/I For Median resistance - For calculating mech mod's body resistance


The voltage output from a regulated mod is not the battery voltage (like in a mechanical mod).
It is converted using a combination of buck/boost and/or PWM (pulse width modulation), or a pulsed DC circuitry to achieve the desired wattage to fire the atomizer.
At wattages requiring less than the battery voltage, the mod will either buck the voltage down or more often pulse the DC voltage on and off to get the desired wattage.
At wattages requiring higher voltage than the battery has, the boost circuitry will boost the battery output up to get the desired wattage.
This boost circuitry has some energy loss, so it will use a little more watts from the battery than at a lower voltage output from the battery.

The amps you see on the screen is not the current drawn from the battery. This reading is amps being delivered to the coil, not what is being drawn from the battery. With a regulated device, it separates coil from the battery. The battery never sees what resistance you are using, it only sees the power you are using. Your current draw at the battery is based on your requested power, battery voltage plus a little extra due to device efficiency. As your battery voltage depletes, current goes up in order to meet your power demand. This is why when calculating battery current draw with a regulated device we use the lowest usable voltage (device cut off voltage).

To determine the needed amperage for a regulated device take your operating wattage and divide by the amount of cells. This will equal Wattage per battery.
Then take your Wbattery, divide by your cut off voltage, which is usually 3.2 volt, then divide by the efficiency of the device, safe to use 90% efficient if unknown. This will equal your amps draw per battery.This works for series or parallel devices. It does not matter how they are connected as we are already taking that into account when we calculate the max power for each battery.

You can calculate current draw using this formula:I=P/number of batteries/Vcut off/0.9
P= the selected wattage
V=cut off voltage (usually 3.2 volt)
0.9=CPU average efficiency


Let's say you have a 200W device and a pair of new batteries with a 15A CDR.

In this case the max wattage you can set without stressing your batteries,can be calculated using this formula:
P=V cut off x CDR x number of batteries x 0.9 (CPU efficiency).
So with the batteries you have it will be:
3.2 x 15 x 2 x 0.9=86.4 Watt


For an example, Geek Vape Aegis Legend 200W regulated mod, has 9V max voltage output and 50A current output limit.

To achieve 200 watt:

A) Resistance must be not higher than 0.405ohm due to voltage limit.

B) Resistance must be not lower than 0.08ohm due to current limit. (Aegis legend can fire down to 0.05ohm in power and bypass mode)

R=resistance required to achieve max wattage.
V=max voltage output of device (9V)
P=max wattage of device (200 watt)
I=max current limit of device (50A)

Coil resistance within a regulated device is irrelevant based on current draw from the batteries. But coil resistance still has to fall within the regulator's output limitations for a prescribed wattage. Every board has its limitations in what it is able to output in terms of max wattage, max voltage and max current. Max wattage can not be met if a coils resistance dictates a voltage or current that exceeds the boards limitations. High resistance at high wattage requires high voltage. Low resistance at high wattage requires high current.