Aquarium Heater Wattage
Calculator
Results
- Heater power (W)
- 100
- Energy to raise the temperature (J)
- 4,186,000
- Energy to raise the temperature (kWh)
- 1.162777
- Hours to reach the rise at full power
- 11.627777
Pool and aquarium results
| Heater power (W) | 100 |
| Energy to raise the temperature (J) | 4,186,000 |
| Energy to raise the temperature (kWh) | 1.162777 |
| Hours to reach the rise at full power | 11.627777 |
formula-map diagram
- Heater power (W)
- 100
- Energy to raise the temperature (J)
- 4,186,000
- Energy to raise the temperature (kWh)
- 1.162777
- Hours to reach the rise at full power
- 11.627777
Pool and aquarium relationship
Formula
W = volume(L) × W/L; Q = m × c × ΔT= 100
Note
This is a simplified model: it applies a standard geometric or physical formula to the numbers you entered. Volumes assume a regular shape and an even average depth, and the kidney shape uses the common 0.45 × (A + B) × L area approximation. Chemical doses convert a target change into a product mass using the strength or label dose you enter, because the amount of active ingredient varies from product to product; they ignore pH, temperature, buffering, sunlight, bather load and existing chemical interactions. Heating uses Q = m × c × ΔT with c = 4186 J/kg·K and ignores heat losses to air, ground and evaporation; evaporation and cover figures use the rate you enter, not local weather. Aquarium stocking by surface area is a rule of thumb, not a biological limit. Always follow the product label and test the water before and after dosing, and consult a pool or aquarium professional for anything you are unsure about.
More in Pool and aquarium
See all →Frequently asked questions
How does the calculator turn tank size into a wattage recommendation?+
It uses a rule-of-thumb power density, roughly 3-5 watts per liter (or about 3-5 watts per gallon in some simplified versions, though the metric figure is the more physically grounded one), scaled up for a larger desired temperature rise above the room's ambient temperature. A bigger gap between room temperature and target tank temperature needs proportionally more wattage to maintain.
Why does room temperature matter as much as tank size for heater selection?+
A heater's job is to offset ongoing heat loss to the surrounding room, and that heat loss is driven by the temperature difference between the tank and the room, not by tank size alone. A tank in a cool basement needs a notably stronger heater than the same size tank in a warm, insulated room, even though both hold the same volume of water.
Is it better to slightly oversize an aquarium heater?+
A modest oversizing, especially when paired with a reliable external thermostat/controller, reaches target temperature faster and copes better during unusually cold spells, but a heater that's too oversized without good temperature control risks overshooting and stressing fish if it malfunctions in the 'on' position. Many keepers use two smaller heaters instead of one large one, both for redundancy and more even heat distribution.
Why would two smaller heaters be recommended instead of one large one for a bigger tank?+
Splitting wattage across two heaters placed at opposite ends of the tank distributes heat more evenly, reduces the odds of a dangerous temperature spike if one heater sticks in the 'on' position, and provides backup heating capacity if one unit fails. This redundancy matters more as tank size and fish value increase.
Does water movement or tank shape affect the wattage I actually need?+
Yes — a tank with strong surface agitation or in a drafty location loses heat faster through evaporation and convection, needing more wattage than the base calculation suggests, while a tightly lidded, low-flow tank in a warm room may need less. Treat the calculator's output as a solid starting point, then observe actual temperature stability and adjust.