Aquarium Heater Size Calculator
Fill in the values and the answer updates as you type.
How the Aquarium Heater Size Calculator works
A widely used guideline is about 1 watt per liter of water for a rise of 10 °C, scaled in proportion for smaller or larger rises: watts = liters × rise ÷ 10. A 25 percent margin covers cold rooms, drafts, and a heater that ages. In larger tanks, two smaller heaters at opposite ends give even heat and a backup if one fails. Use a heater with a thermostat and check the water with a separate thermometer. Example: Heating 100 liters from 22 °C to 26 °C needs at least 40 W, so look for about 50 W.
Inputs and results
The Aquarium Heater Size Calculator takes 3 inputs and gives 3 results.
What you enter
- Water volume (liters) — starts at 100.
- Room temperature (°C) — starts at 22.
- Target water temperature (°C) — starts at 26.
What you get
- Minimum heater power (W)
- Recommended with 25% margin (W)
- Temperature rise needed (°C)
Example: Aquarium Heater Size Calculator with the starting values
With water volume 100 liters, room temperature 22 °C and target water temperature 26 °C, the calculator returns:
| Minimum heater power (W) | 40 |
|---|---|
| Recommended with 25% margin (W) | 50 |
| Temperature rise needed (°C) | 4 |
Change any value above and the results update straight away.
Aquarium Heater Size Calculator FAQ
How do I use the Aquarium Heater Size Calculator?
Enter water volume, room temperature and target water temperature in the fields, then read minimum heater power (w), recommended with 25% margin (w) and temperature rise needed (°c) in the result panel. The answer updates as you type, and you can press Calculate or Enter to refresh it. Use “Copy link” to share your exact numbers with someone else.
What does the Aquarium Heater Size Calculator calculate?
Heater wattage needed to warm a tank from room temperature. It returns minimum heater power (w), recommended with 25% margin (w) and temperature rise needed (°c) from the 3 values you provide.
What values does the Aquarium Heater Size Calculator start with?
It opens with water volume 100 liters, room temperature 22 °C and target water temperature 26 °C so you can see a working result straight away. Replace them with your own numbers, or press Reset to return to these starting values.
Is the Aquarium Heater Size Calculator free and private?
Yes. It is free, needs no account, and runs in your browser, so nothing you type is sent to or stored on our servers. See the Privacy Policy for details.
Can I rely on the Aquarium Heater Size Calculator for medical or health decisions?
Treat the result as a well-rounded estimate. Real situations often have details a general calculator cannot know, so confirm medical or health decisions with a qualified professional. See the Disclaimer for more.