Pets

What Size Aquarium Heater Do You Need?

Built by Kevin Glover · @gloverbuilds · Verified formula

Calculate the right heater wattage for your fish tank based on volume and room temperature.

📅 Updated April 2026 ✅ Formula verified 📖 4 min read 🆓 Free · No sign-up

In this article

Sizing Your Aquarium Heater
Heater Safety

Faustregeln

1W/L bei <5°C Differenz. 1,5W/L bei 5-8°C. 2W/L bei >8°C. Deutsche Wohnungen (20-22°C) mit Tropenfischen (26°C): 1W/L reicht meist. 200L: 200W Heizer. Im Winter in schlecht isolierten Raeumen: 1,5W/L.

Sicherheit

Heizer-Defekt (Dauerbetrieb) ist die haeufigste technische Todesursache im Aquarium. Externer Temperaturcontroller (20-40 €) als Backup empfohlen.

⚡ CalcWolf Insight

A sudden temperature drop of 5°F+ can trigger Ich (white spot disease) in tropical fish — the most common aquarium disease. A reliable heater with a temperature controller is cheaper ($40-60 total) than treating a tank full of sick fish ($20-40 in medication plus potential fish losses). Prevention is always cheaper than cure in fishkeeping.

Frequently asked questions

Wie viel Watt?▾

In deutschen Wohnungen: 1W/L. 200L = 200W. Kalter Keller: 1,5-2W/L.

Brauche ich einen Heizer?▾

Tropenfische (24-28°C): ja. Kaltwasser (Goldfisch): meist nicht noetig.

✓ Math logic verified against primary sources → See our verification process

Kevin Glover · @gloverbuilds

Founder, CalcWolf · GLVTS · Blickr

All formulas sourced from primary references — IRS publications, peer-reviewed research, and official standards. Results are tested against independent reference calculators before publishing. Rates and brackets updated when official sources change. Editorial policy →