Ohm’s law is the scientific theory of circuitry that establishes the relationship between voltage, resistance, and amperage. The law is named after the German physicist Georg Ohm who published an early version of the equation in 1827.

In vaping, Ohm’s law is most commonly used to ensure safety when building coils or using an unregulated (or mechanical) mod, but it can also help to gauge the appropriate resistances, amperage, and voltage to use when building on a regulated mod.

You may have heard stories about vapes catching fire or exploding. This is because Ohm’s law was not being adhered to and batteries were not being used correctly in unregulated devices. When the amperage of a circuit exceeds the limit dictated by the power source, it can result in electrical shorts leading to fire, explosions, and harm to you and those around you.

### The Major Players

There are three main elements that you’ll want to understand in order to use Ohm’s law:

**Amperage (Amps)**—the rate of flow of an electrical current within a circuit.

**Voltage (Volts)**—the amount of pressure on electrons leaving the power source.

**Resistance**—the ease with which electrons can pass through a conductive material. In vaping, resistance will remain constant as it is determined by the coil you are using.

These three factors create a triangular relationship that are dependent on one another. Resistance is the only constant in this case, as resistance is determined by the size of the coil and gauge of its wire. Amperage and voltage, on the other hand, are variables, and will fluctuate based on the resistance and rate of the other variable factor.

### All About Batteries

Before we get further into calculating Ohm’s law, it’s important that you understand a few things about batteries.

All batteries have a maximum voltage rate of 4.2V at full charge and will decrease in voltage as the charge depletes. When two batteries are run in parallel (together at the same time), they will still maintain a fully charged voltage rate of 4.2V combined. However, when two fully charged batteries are run in series (one after another), their combined voltage will total 8.4V.

It is also critical that you note your battery’s amperage limit when using an unregulated mod. Each brand of battery will have an amp limit, which is the maximum amperage the battery can be used at safely without risk of harm. Exceed this limit, and you’re in the danger zone.

### Calculating Ohm’s Law

Ohm’s law is expressed as **I = V / R**, where I represents amperage, V represents voltage, and R represents resistance.

So…

**Amps =**** Voltage / ****Resistance **

Depending on the information you have in hand, you can calculate the missing element.

Here are the other formations of this equation:

**V = I x R (Voltage=Amps x Resistance)**

**R = V / I (Resistance = ****Voltage / ****Amps)**

### What About Wattage?

One variable that has been missing from this discussion is wattage. Wattage (W) is the rate of electrical power consumption, and is the factor that controls the heat of your coil. A lower wattage will provide a cooler current (normally less vapour), while a higher wattage will produce more heat (normally more vapour).

When you set your wattage on a regulated mod, it’s not actually the wattage that is being changed, but rather the voltage, bringing your wattage level to the range you set.

Mathematically speaking, the equation to calculate wattage is

**W = I x V** (**Wattage = Amps x Voltage)**

or **W = V² / R (Wattage = ****V² / R)**

### Ohm’s Law Made Easy

If you don’t want to carry all this information with you all the time, or aren’t a fan of math, it’s no problem! There are several different Ohm’s law calculators out there that will do the work for you. All you have to do is plug in two of the three variables.

Here’s a link to our preferred **Ohm’s Law calculator**.

**Related**: Coil Building for Beginners, Battery Safety