How much does an aquarium, 100 litre cost to run?
About 0.63p an hour in the UK and 0.44¢ an hour in the US. An aquarium, 100 litre draws about 40 W for roughly 60% of the time it is switched on, so it averages 24 W. The heater is most of it; the air pump and filter are a few watts each and are what actually keeps fish alive.
What it costs, by how long it runs
| Running for | kWh | UK | US |
|---|---|---|---|
| 10 minutes | 0.004 | 0.11p | 0.07¢ |
| An hour | 0.024 | 0.63p | 0.44¢ |
| An 8-hour night | 0.19 | 5.1p | 3.5¢ |
| A full day (24 hours) | 0.58 | 15p | 11¢ |
| A month at 8 hours a day | 5.76 | £1.52 | $1.06 |
UK prices use the Ofgem price cap for 1 October to 31 December 2026 (direct debit, average across England, Scotland and Wales, with no VAT on electricity this winter): 26.32p per kWh (Ofgem). The standing charge of 54.83p a day is paid whatever you run, so it is left out. US prices use the US average residential price for June 2026 from the Energy Information Administration: 18.34¢ per kWh (EIA). Your own tariff is on your bill; scale the figures by it.
Measure your own
These are typical figures for a typical unit. A plug-in energy monitor between the socket and the appliance shows the real watts and adds up the kWh, so after a day or a week you know exactly what it costs on your tariff.
Compared with similar appliances
| Appliance | Average W | UK per hour | US per hour |
|---|---|---|---|
| Baby monitor | 6 | 0.16p | 0.11¢ |
| Aquarium, 100 litre | 24 | 0.63p | 0.44¢ |
| Hair straighteners | 24 | 0.63p | 0.44¢ |
| LED Christmas tree lights (500 bulbs) | 35 | 0.92p | 0.64¢ |
| Garden inflatable (Christmas or Halloween) | 50 | 1.3p | 0.92¢ |
| Dehumidifier, 12 L/day | 150 | 3.9p | 2.8¢ |
| Well pump (1/2 hp) | 200 | 5.3p | 3.7¢ |
| Cordless mower battery charger | 200 | 5.3p | 3.7¢ |
| Incandescent Christmas tree lights (500 bulbs) | 204 | 5.4p | 3.7¢ |
| Sump pump | 240 | 6.3p | 4.4¢ |
| Heated clothes airer | 300 | 7.9p | 5.5¢ |
| Hair dryer | 1,800 | 47p | 28¢ |
| Electric car (3-pin "granny" charger) | 2,300 | 61p | 26¢ |
Running it in a power cut
See which power station will run an aquarium, 100 litre, and for how long.
Appliance draw modelled on web.archive.org. The US Department of Energy retired this page in 2025; the link is the Internet Archive's June 2024 capture. The figures remain typical ranges for a typical unit, not a specification.
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