Feature: How much does it cost to charge your tech?
Jim Martin reveals the cost of powering your tech
In the UK, we typically pay around 10p per kWh of electricity. This is the standard measurement of how much energy you use. Your monthly electricity bill shows how much you’ve used, and you can keep tabs on usage by looking at your electricity meter. If you want to measure how many watts a device draws when charging (or in use) you can
buy a power meter for around £10, which plugs into the mains socket and has a passthrough socket for the device in question. Its readout will tell you the current power draw, but it should also have a mode where it monitors power over time and offers an average power draw – useful in the case of laser printers and other products that don’t draw a constant amount of power.
Getting back to kWh, it stands for kilowatt hour. If you had a 1000-watt bulb and turned it on for an hour, it would use 1kWh (1000 watts = 1 kilowatt). Or, if you have a 2000-watt kettle, it will use 1kWh in 30 minutes. If you know how much power is being used by an appliance, you can work out how much it costs to use them.
Cost to charge an iPad
Let’s use an iPad Pro as an example. It takes 4.5 hours to charge from empty to full, and it has a 12W charger. So it will draw 12W for 4.5 hours, assuming you leave the tablet powered off and don’t use it.
12W, in kilowatts is 0.012kW. So multiplying this by 4.5 hours is:
0.012x4.5 = 0.054
So the iPad Pro uses 54W to charge. To work out the cost, it’s a simple case of multiplying your cost per kilowatt by the amount of power used:
10 x 0.054 = 0.54p
Yes, that’s correct: half a penny. The yearly cost to charge an average tablet is roughly £1. As we said,
it’s less than you think. We’ll leave you to work out the cost of charging a phone – it’s less than a tablet, of course – but we will offer an example calculation for the cost to charge a laptop.
Cost to charge a laptop
Taking the Dell XPS 13 as an example, it takes three hours to charge from empty to full. It has a 45W charger, so the calculation is as follows:
0.045x3 = 0.135 10x0.135 = 1.35p
And just for interest’s sake, the average kettle draws 2.2kW (2200W) and takes two minutes and 30 seconds to boil one litre of water, enough for four cups of tea. First convert minutes to hours:
2.5/60 = 0.0417
Then calculate the energy use:
2.2 x 0.0417 = 0.917 10 x 0.917 = 0.9p
So it costs about 1p in electricity. Bear in mind these figures don’t include the ‘standing charge’, which is a fixed fee most people pay their energy supplier in addition to the cost of the energy they actually use. This varies, but is around £100 per year, and needs to be factored in to get the true cost of using any electrical appliance. If you’re doing your own calculations, first check what you pay per kWh and the standing charge you pay.