Reptile Tank Heater Wattage Calculator
Estimate the heating wattage a reptile enclosure needs from its size and the temperature it must rise above the room, then round to a real bulb.
How it works
Watts ≈ volume(gal) × 2.5 × (target − room)°F ÷ 22 × enclosure factor · then round up to a stocked bulb size
Heat output has to replace what the enclosure loses, which grows with both its size and how far above room temperature you want the warm side. This estimate is calibrated so a typical 40-gallon glass vivarium raising temperature about 22°F lands near 100 watts, then scales for larger tanks, bigger temperature gaps and how well the enclosure holds heat. It sizes the heat source — but the single most important rule is to run any heater on a thermostat, because the target basking temperature, not the wattage, is what keeps the animal safe.
Worked example
A 40-gallon glass vivarium in a 68°F room targeting a 90°F basking spot must rise 22°F: 40 × 2.5 × (22/22) × 1.0 = 100 W, so a 100 W basking bulb on a thermostat is the starting point.
Frequently asked questions
Why must I use a thermostat?
Wattage only estimates the heat needed; the actual temperature depends on room conditions, bulb distance and the enclosure. A thermostat measures the real temperature and cuts power when it is reached, preventing both dangerous overheating and thermal burns. Never run a reptile heat source unregulated.
Does this cover UVB as well?
No. This is about heat only. Many reptiles also need UVB lighting for calcium metabolism, which is a separate fixture chosen by the species and enclosure height — a heat bulb does not provide usable UVB.
What are the exact temperatures my reptile needs?
This tool uses whatever target you enter, but the correct basking and cool-side temperatures are species-specific — a bearded dragon, a ball python and a leopard gecko all differ. Look up your species’ thermal gradient and set the target accordingly.
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Educational estimate only — not veterinary advice. Always consult a licensed veterinarian before dosing, treating, feeding, or making care decisions for any animal.