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Ohm’s Law: Everything a Vaper Needs to Know

Ohm’s Law: Everything a Vaper Needs to Know

John Boughey |

Last fact-checked 15 January 2021 | Report a factual error on this article

Ohm’s law lies at the heart of a safe and enjoyable vaping experience — if you build your own coils, you definitely need to understand it. But what if you use a pod system or a vape pen? How important is Ohm’s law for the typical British vaper with little or no interest in rebuildable atomisers?

Prior to founding Gourmet E-Liquid with Gareth I worked as an electrical engineer, so I understand Ohm’s law inside-out. In this week’s article, I’ll explain the basics of electrical resistance and show you how it all relates to battery safety in your vape device. I’ll do my best to simplify Ohm’s law for you, and tell you everything you know to keep yourself safe. 

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When do you need to learn Ohm’s Law?

Ohm’s law actually isn’t required reading for most beginner vapers. If you use a pod system or a basic vape pen, you could vape away happily for years without understanding the first thing about Ohm’s law. 

You only really need to understand Ohm’s law when you start vaping with an RDA (learn all about RDAs here), and/or when you start cutting your own coils. When you cut your own wire coils, you run the risk of changing the electrical resistance running through your vape device … and that’s where things get dangerous if you don’t know what you’re doing. 

Ohm’s Law: How it Affects Your Battery

Most of us have heard horror stories about e-cigarette batteries exploding or catching fire. These stories all stem from a basic lack of knowledge of Ohm’s law. 

I’ll show you the exact formula later on in this article, but in essence, Ohm’s law says that if the electrical resistance in your vape device drops, the power running through your e-cig goes up.

If you drop your vape’s resistance too low (by installing an inappropriate coil, for instance), the increase in power can potentially push your battery beyond its safe limits … and that’s when things get dangerous.

What is an Ohm?

To explain this in more detail, let’s start by looking at what an Ohm actually is, and how ‘Ohms’ fit in with what your vape pen is doing when you push that fire button. 

The symbol for Ohm is Ω, or omega. If you already have a box mod, you might recognise this symbol from the settings panel on your device. When people talk about sub-ohm vaping, they’re talking about vaping on a device where the resistance of the coil is less than one ohm (0.2Ω, 0.5Ω and so on).

Named after Bavarian physicist and mathematician Georg Ohm (the man who discovered Ohm’s law almost two centuries ago footnote 1), Ohms are used to measure the resistance of an electrical circuit. 

To understand resistance, you first need to know a little about current and voltage. Basically, electricity is measured in a few different ways... 

    • There’s the current (measured in amperes (A)), which is best understood as the rate of flow of electricity through a circuit (think of it as the ‘speed’ of the electricity running through your vape device). 
    • There’s also the voltage (measured in volts (V)), which is the ‘amount’ of electricity in a circuit (technically, the “electric potential”). When you clip a heating coil into your e-cigarette and push the fire button, the high voltage contained in the battery pack is what causes the metal coil to heat up and evaporate your e-liquid. 
    • There’s also the wattage (measured in watts (W)), which is a combination of the current and the voltage (current x voltage = wattage). When someone talks about wattage, they’re talking about electrical power

If you need more detail, this GCSE revision video on YouTube gives a good explanation of voltage, current, Ohm’s Law and resistance:

Why do we need Ohm’s law?

Your vape device is made up of conductors and insulators. The conductors in your vape device (components like the heating coil, the internal wiring and the contact points at either end of the battery) make it really easy for electricity to get where it needs to go, while the insulators (things like the battery casing and the mouthpiece) are what protect you from getting an electric shock when you vape. In other words, insulators 'throttle’ the current in an electrical circuit, whereas conductors have the opposite effect. 

In the UK, if you buy an e-cigarette or a pod system from a registered retailer, the engineers who created that product will have made sure that the power in the battery balances perfectly with the resistance of the coil. You just need to push the fire button, and you’ll get a good mouthful of vapour.

If you build your own coils, however, you can choose the type of metal the coil is made out of, and how long the coil is. This means that you can change the electrical resistance of your vape device, and when you do this, you change the current and voltage levels running through your battery. If your battery is exposed to a higher current than it was designed to handle, then it could catch fire (footnote 2) This is why a solid working knowledge of Ohm’s law is so important.

Using Ohm’s law as a guide, you can tailor the resistance of your coil to match your battery’s current and voltage settings, and vice versa. This means that you can cut and build your own coils from a spool of specialist wire (we sell this wire here, by the way!) and you won’t risk a battery fire every time you vape your favourite e-liquid. 

Ohm’s Law Conversion Tables

Ohm’s law states that the voltage in your vape device, divided by the resistance, equals the current. Using this simple formula, if you know your resistance and you know your voltage, you’ll be able to calculate your current and make sure that it’s within the safe range of your battery. 

Just fill in the blanks on the chart below and you’ll be able to calculate whatever value you need:

To calculate CURRENT (A):
Voltage (V) ÷ Resistance (Ω) = Current (A)
To calculate VOLTAGE (V):
Current (A) x Resistance (Ω) = Voltage (V)
To calculate RESISTANCE (Ω)
Voltage (V) ÷ Current (A) = Resistance (Ω)


I hope this layman’s guide to Ohm’s law has given you enough information about what Ohm’s law actually is and how it fits into most vapers’ lives. If you have any other questions, please feel free to ask us — we’re always happy to help. 

Just one last thing to mention: Some people think that they’re safe to do whatever they like with their coils if they use a regulated box mod. Regulated box mod devices all contain a built-in safety chip which breaks the circuit if the current in your vape device becomes too strong, but that doesn’t mean it’s a good idea to take chances with your heating coil.

Our advice is to only use regulated box mods regardless of what type of coil you want to use, and to make coils that stay well within the normal safe settings of your device.  Sub-Ohm vaping is great fun, but there’s no sense in risking an injury just to get a slightly bigger vapour cloud.

Stay safe and happy vaping!

 - John Boughey

Links & Citations

Footnote 1:

Georg Ohm wrote a book, published in 1827, titled “Die galvanische Kette, mathematisch bearbeitet” (or The Galvanic Circuit Investigated Mathematically, in English), which covers Ohm’s law. Ohm’s law is defined on

Footnote 2:

All of the vape batteries we sell (see  will quote a CDR, or Continuous Discharge Rate. This is the maximum current that a battery can handle before it starts to suffer damage. 

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