Size Your Heater in Seconds
Enter your tank volume and the temperatures involved, and get a wattage to aim for – sized to real heaters we stock, not just a generic chart.
Based on roughly 1.3 watts per litre for every 10°C you need to raise the water above your room's coldest point, plus headroom for cold snaps. A guide to start from, not a guarantee – see the FAQ below for what else affects it.
FAQ
What size heater do I need for my aquarium?
As a starting point, aim for roughly 1.3 watts per litre for every 10°C you need to raise the water above your room's coldest point, then add some headroom – that's what the calculator above works out for you. It's a guide, not a guarantee: a well-insulated tank with a lid needs less than an open-top tank in a draughty room, and a sump adds extra surface area that can cool faster than the display tank. If you're between two wattages, size up rather than running a heater at its rated limit continuously.
Should I use one heater or two?
For most tanks under about 200 litres in a normally heated room, one correctly-sized heater is enough. Above 200L, in a cold room, or with livestock where a stuck-on or failed heater would be serious – a full reef tank, for example – splitting your wattage across two heaters is worth it. It halves the temperature swing if one fails, and leaves you with a working heater while you replace the other.
Where should I place an aquarium heater?
Near an area of good water flow – close to a filter outlet or powerhead – so heat spreads evenly instead of pooling in one spot. Keep it off the substrate, and only mount it horizontally if it's rated for that (check the listing first in a shallow tank). Position it somewhere you can see the indicator light at a glance.
Can I use any heater in a marine or reef tank?
No – check the listing first. Some heaters, like the Fluval T-Series below, are built for freshwater only and aren't rated or warranted for saltwater. Others, like the Bioscape Tropic and Bioscape PRO ranges, are rated for both fresh and marine. If you're heating a reef or marine tank, stick to a heater explicitly listed as marine-safe.
Shop Heaters
Wattages and rated tank sizes above are from each manufacturer's own specifications. Always check the current listing for the exact model and size before buying.