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How to Calculate Electricity Costs

How much electricity does it take to run a home garden and how much is it going to cost me? These are two very important questions to consider when setting up your indoor garden/grow tents. Unfortunately, there isn’t really a straight forward answer there as it completely depends on the size and scale of your system; a 2’ x 4’ grow tent with a light or two is going to use a lot less electricity than a 10’ x 20’ tent with multiple lights, fans, etc.. In addition, where you live might play a major part in how much you are charged by your power provider for that electricity. Ultimately it is up to the grower to crunch these numbers before getting started to determine if the “juice is worth the squeeze”, but we are hoping this quick and easy guide will help you come to an informed decision!

Before we dive into calculating your energy costs, we first need to define some important variables/factors that you need to understand about energy use:

  • Amperes (A) (commonly called “amps” and represented as "I" in formulas): This is the unit of measurement for electrical current. This is basically the speed in which electrons flow through a conductor; think of it like water flowing through a faucet - when you turn the valve all the way open you get a higher rate of water flow. Similarly, the higher the amps, the more current is working its way through the circuit.
  • Ohms (Ω) (commonly referred to as "resistance" and represented as "R" in formulas): This is the unit of measurement for resistance and tries to slow down the movement of electrons through a conductor. In the water analogy, the resistance would be the diameter of your pipe. The bigger the pipe, the less the resistance, and the more water can be moved through the pipe and vice versa.
  • Voltage (V) (commonly called “volts” and represented as "U" in formulas): This is the unit of measurement for electrical potential - measuring the amount of electrons that exist in a circuit. Going back to the water analogy, the voltage would be an equivalent to water pressure - how much water is physically in the pipes and how much is being pushed through?
  • Wattage (W) (commonly called “watts” and represented as "P" in formulas): This is the unit of measurement for power - basically measuring how many electrons are moving through a conductor; basically volume of electrons multiplied by the speed. You can increase power by either increasing amps and/or volts.
  • Simple Formula for Watts: P (Watts) = U (Volts) * I (Amps)
  • Kilowatt (kW): A Kilowatt is simply 1,000 Watts. Example: 2kW = 2,000W.
  • Kilowatt-hour (kWh): This is the measure of how many watts would be used in an hour. For example, if you had a 1,000W light running for 1 hour, that light would be using 1kWh.

Now that we have the basics laid out, let’s use some hypothetical real world examples to show how your power bill might be calculated. Generally power companies charge their customers based on the number of kWh used in a given amount of time (usually monthly or 30 day increments). Some power companies have tiered pricing as well where kWh during the day might cost less than kWh used at night or peak hours. Some other companies will also charge you a certain amount for a set amount of kWh and then more when you reach that threshold (for example: $0.10/kWh for the first 100 kWh and then $0.12/kWh for the next 100, and so on). This will change from region to region, so make sure you find out what your power supplier is charging so you can calculate your costs.

So for example let’s say your power company charges a set rate of $0.10/kWh. You have 2 lights running at 1,000 Watts, a fan at 50 Watts, maybe a pump at 100 Watts (just making up numbers here) and let's say you’re running all of this for 12 hours per day. You’d be looking at spending $2.58/day (or $77.40 in 30 days).

  • 1,000W + 1,000W + 50W + 100W = 2,150W
  • 2,150W / 1,000 = 2.15kWh
  • 15kWh * 12 hours = 25.8kWh
  • 25.8kWh * $0.10/kWh = $2.58
  • $2.58 * 30 days = $77.40

Pretty simple, right? There's a ton of variety to what your equipment requires, what your power company charges, and to how long you will be running your system; this can make things intimidating, but really it’s not that difficult to figure out as long as you have all the details. We here at Grow Tents Depot would be happy to help you figure out these costs if you need help - just hit us up! Until then, happy growing!


Hi Kenneth – thank you for your question! Your math is correct – the only variables here you need to look out for are if your energy company charges different rates at different times of day (which is common, unfortunately) or if you have a tiered plan. What I mean by that is some energy companies will move you up a tier in pricing if you have used a certain number of kWh in a billing period. Other than that, you nailed it!

Grow Tents Depot

i bought the 3 by 3 by 6 grow tent. i used the formula that you sent me to calculate the electricity cost. 240 watt light + fan 50 watts + humidifier 30 watts = 320 watts /1000 = .32kwh * 18 hours = 5.76 kwh * .20= 1.152 * 31 = 35.712 dollars a month. is this correct?

kenneth H larivee

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