What is Ohm's Law?

If you're keen to start building your own coils or are simply interested in the science behind how vaping works, learning ohm's law is a necessity. This is a formula that calculates the relationship between voltage, resistance, and current in an electrical circuit. 

While ohm's law may seem confusing or tricky at first, most vapers pick it up quickly. You might even remember it from your secondary school physics lessons!

In this guide, we'll explain in simple terms how ohm's law works and how you can use it. By the end, you'll know everything you need to know about ohm's law for vapers. 

So, let's get started. 

Who needs to know ohm's law?

Not every vaper needs to have a good understanding of ohm's law. In fact, if you're happy vaping with your disposable vape, pod kit, or Mouth-To-Lung vape pen, an understanding of ohm's law is far from necessary. 

You only need to know ohm's law if you:

  • Want to start using an RBA (Rebuildable Atomiser) vape
  • Are keen to build your own coils
  • Are ready to use an unregulated or mechanical mod 
  • Want to learn the science behind vaping

Why is ohm's law useful for vaping?

First, some context

In sub-ohm vaping, vapers want coils that heat up faster, vaporise e-liquid more quickly, and therefore produce bigger, denser clouds of vapour for the best possible vaping experience. In order to do this, you need more power to reach the vape coils.

However, there's a limit to how much power you can push through your vape device, so instead of using more power output from the batteries, vapers found another way to increase the power: lowering the resistance. With a lower resistance, the current increases, and therefore the power increases. 

This is what caused the rise of sub-ohm vaping, a style of vaping that uses coils (atomiser heads) with very low resistances. Originally, any coil resistance below 1 ohm was considered very low, giving rise to the name 'sub-ohm vaping'. However, with ever-improving technology, we can now use coils with very low resistance such as 0.2 or 0.1 ohm. 

For more on sub-ohm vaping, check out our blog on cloud chasing, aimed at beginner vapers.

So, back to ohm's law

A good knowledge of ohm's law is essential for vape safety when using an RBA or mechanical mod. Being able to do these calculations allows you to keep your vape within safe limits.

As the resistance is increased, current and power decrease. On the other hand, as you decrease resistance, current and power will increase. In practical terms, this means that using a coil with a resistance too low could potentially push your vape batteries beyond safe limits. To avoid this danger, you need to use ohm's law to calculate a safe resistance for your coils. 

Some useful definitions 

To explain ohm's law, we need to start with some terminology. 


Current (I) is the rate at which charge flows through a surface such as the wire in your circuit. Current is measured in Amps (A).


Voltage (V) is essentially the amount of electricity in a circuit. It is the measure of the potential difference in charge between two points. A higher voltage between two points (such as the positive and negative battery terminals) means that more energy can be gained using the same amount of charge compared to a lower voltage. Voltage is measured in Volts.


Resistance (R) refers to a material's tendency to resist the current. In a material with a lower resistance, electrons can flow faster and more easily, whereas materials with a higher resistance result in electrons flowing more slowly. As a result, low resistances mean that more power can flow through your device, which is how sub-ohm vaping works (we'll talk more about sub-ohm vapes later). Resistance is measured in ohms (Ω). 

Electrical power

Electrical power (P) refers to the amount of work being done by electricity in a given moment. This is calculated by multiplying voltage in Volts by current in Amps to find the Wattage (W).

Ohm's law explained

Ohm's law helps you calculate the resistance between voltage, current, and resistance in an electrical circuit. The law is a set of formulae that are often represented in a triangle. 

The three key elements of an electrical circuit are:

  1. Voltage (V), which refers to the voltage of the battery
  2. Current (I), which refers to the amperage drawn by your coil
  3. Resistance (R), which refers to the resistance of your coil in ohms

The triangle is used to remind us of the relationship between these three elements. To find V, multiply I by R. To find R, divide V by I, and so on.

Don't worry if this still seems confusing -- we'll look at each calculation in more detail below.

To calculate voltage

Voltage (V) is at the top of the triangle, so to calculate it you'll need to multiply current (I) by resistance (R). 

V = I x R

To calculate current

Current (I) is calculated by dividing voltage (V) by resistance (R).

I = V / R

To calculate resistance

Resistance (R) is calculated by dividing voltage (V) by current (I).

R = V / I

What about power (wattage)?

Power (P) in watts is not included in the triangle, but it's important for vapers to know because this is the unit used by vape batteries. Fortunately, it's easy to calculate. The power or wattage is found by multiplying current (I) by voltage (V).

P = I x V

Want to check your calculations? We're big fans of this ohm's law calculator which lets you input the values and quickly get results. 

Now let's apply this to vaping

With the physics lesson out of the way, it's time to look at what all this actually means for your vape. 

Sub-ohm vaping

If you're new to the world of vaping, this knowledge may have inspired you to try out your first sub-ohm vape. A lower coil resistance is linked to more current and power, helping you achieve bigger clouds and a warmer, denser vapour from your vape. Sub-ohm devices are designed for DTL (Direct-To-Lung) vaping which allows you to enjoy that dense and delicious vapour. 

Side note: sub-ohm vaping with a store-bought vape doesn't require any specific knowledge of ohm's law. As long as you use the correct vape coils for your setup, the manufacturers have already carefully calculated and tested the vape hardware to ensure your safety. 

If you're interested in trying sub-ohm vaping for the first time, check out our range of advanced kits and buy your sub-ohm replacement coils here. Don't forget to buy an e-liquid with a high VG content, such as one of our 70% VG shortfill e-liquids.

Coil building

A good understanding of ohm's law is essential for coil building for your RDA, RDTA, or RTA

Building your own coils allows you to set the resistance to your preferred level. This is done by changing the type of material the coil is made of, the thickness (gauge) of the wire and the length (wraps) for different ohm resistances. Coil building can be pretty tricky so if you're new to RBAs we recommend starting with pre-built coils. You can learn more about pre-built and DIY coils here

Mech mods

In a mechanical mod, also called a mech mod or unregulated mod, there are no circuit boards or built-in safety protections. Without screens or settings, it's entirely down to the individual vaper to ensure that they are vaping safely. They will use ohm's law to calculate an amperage limit for the batteries and stay below the maximum output.

We recommend that only the most confident and experienced vapers use mech mods because making a mistake can be extremely dangerous. Remember the horror stories about vapes exploding or catching fire? It's just not worth the risk! 


Although ohm's law may seem initially daunting to vapers who haven't thought about volts and battery wattage since GCSE physics, taking some time to learn the rules can enhance your vaping. 

Here at Vaping 101, we cater to vapers of all preferences and experience levels. Whether you're a dedicated disposable user, in the market for your first sub-ohm device, or are stocking up on coil wire for your 100th build, we have everything you need for your vaping habits. 

Don't forget to check out our weekly sale for the best vape deals around!

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