Heat Lamp Wattage Calculator

Calculated Watts is driven by the temperature difference between Target Basking Temp and Room Temperature — not by either figure alone — multiplied by Enclosure Volume and an insulation coefficient set by Enclosure Material. Because that temperature difference is a subtraction rather than a raw value, a given percentage change in Target Basking Temp near its default swings the difference (and therefore the wattage) proportionally more than the same small percentage change in Enclosure Volume near ITS default — but Enclosure Volume is also allowed to range much further in absolute terms (from a 5-gallon terrarium up to a 500-gallon enclosure), so across the calculator's full input ranges, a large enough enclosure swing moves Calculated Watts by far more than any realistic basking-temperature adjustment could. Room Temperature works the opposite direction from Target Basking Temp: raising it shrinks the temperature difference and therefore lowers Calculated Watts, all the way down to zero if Room Temperature ever meets or exceeds Target Basking Temp — the formula floors wattage at zero rather than returning a negative heating requirement in that case. Enclosure Material sets a fixed multiplier reflecting how much heat each material type loses (screen- top glass loses the most, PVC/wood the least), scaling every wattage figure up or down. This is a simplified thermal model, not an engineering heat-loss calculation — it does not account for room airflow, enclosure sealing quality, ambient humidity, or the specific bulb's beam angle and distance from the basking spot, all of which affect real-world results.

Recommended bulb (W) is capped at 250W per fixture, the largest standard basking-bulb size — for large enclosures and/or large temperature differences, Calculated Watts can exceed what a single bulb can supply. Rather than silently recommending an undersized bulb in that case, the calculator switches to a multi-fixture recommendation: Fixtures Needed reports how many 250W bulbs are required to cover Calculated Watts, and Multi-Fixture Note spells out the total. Monthly Electricity is always priced off the full installed wattage across every recommended fixture, not just one bulb, so the cost estimate stays accurate in multi-fixture setups. Basking Surface intentionally runs hotter than the plain ambient-plus-differential figure — it applies a 1.2x multiplier to the temperature difference — because a real bulb's direct hot-spot at the basking perch runs measurably hotter than the enclosure's average air temperature that the wattage model is based on.