The Thermal Gradient
A reptile cannot warm itself, but it can choose where to sit. A thermal gradient is the spread of temperatures across a terrarium that actually gives it that choice.
Key facts
- A thermal gradient is the spread from a warm end to a cool end of the terrarium, letting an animal thermoregulate by moving rather than sitting at one averaged temperature.
- A bearded dragon's basking spot commonly runs around 42-45u{00b0}C (108-113u{00b0}F); a crested gecko's runs far lower, around 28-29u{00b0}C (82-85u{00b0}F) — species figures genuinely differ this much, and that is expected.
- The basking spot needs an infrared thermometer aimed at the surface itself — a plain air thermometer measures something different.
What a thermal gradient is, and why it matters
The idea is simple: a terrarium should have a spread of temperatures from a warm end to a cool end, not one averaged temperature throughout. Since a reptile cannot warm or cool itself internally, it thermoregulates by moving between the warm and cool zones — a gradient is what physically gives it that option.
Real numbers — and why they differ this much by species
A bearded dragon's basking spot is commonly cited at roughly 42-45°C (108-113°F), with the cool end of the terrarium around 25-29°C (77-85°F).
A crested gecko — a considerably cooler-tolerant species — runs much lower: basking area around 28-29°C (82-85°F), ambient around 24-28°C (75-82°F), and a cool zone around 21-24°C (70-75°F); sustained temperatures above roughly 29°C (85°F) are linked to heat-stress risk.
These two sets of figures — nearly double one another at the basking spot — make the point clearly: there is no universal "reptile temperature." It is set entirely by species, so check the guidance for your specific animal before setting up its terrarium.
Measuring it correctly
The basking spot needs a non-contact infrared thermometer aimed directly at the heated surface — a fundamentally different reading than a plain air thermometer, which reports ambient temperature rather than how hot the actual surface the animal basks on really is.
The nighttime drop
A modest natural temperature drop at night is considered normal for many reptiles. For bearded dragons specifically, sources cite a floor of roughly 21°C (70°F) that temperatures should not fall below — we did not find a general degree-drop figure that applies to reptiles broadly, so beyond this one example, follow the guidance for the specific species.