What temperature and UVB does my reptile's terrarium need?
Choose your reptile's species to see the recommended temperature range for the hot (basking) zone and the cool zone, plus the UVB requirement and intensity recommended for that species.
Hot / basking zone
38–46 °C
Moderate risk
Where the heat source is (lamp or heat cable/mat) — this is where the reptile goes to raise its body temperature and digest food.
Cool zone (or water)
24–28 °C
Low risk
The opposite side of the terrarium (or the water temperature, for semi-aquatic species) — where the reptile goes to cool down.
UVB requirement
Required
Caution
10.0 (T5 HO) — UV Index 3–4 in the basking zone
A diurnal desert species, one of the most UVB-dependent reptiles kept as pets. Needs a well-defined, hot basking spot to digest food and metabolize calcium.
Keep the basking lamp on for 10–12 hours a day, following the natural day/night cycle.
Always make both sides (hot and cool) available at the same time — the reptile self-regulates by moving between them.
Needs vary by subspecies, age, and health
The values in this calculator are reference averages by species, based on specialized sources. Subspecies, morphs, hatchlings, gravid females, and sick animals may need fine adjustments to temperature and UVB. Always consult a veterinarian who specializes in reptiles (exotics) to evaluate the ideal conditions for your terrarium and your animal's individual health.How the calculation works
Reptiles are ectothermic animals: unlike dogs, cats, and humans, they don't regulate their own body temperature internally and depend on the environment to do it. That's why every terrarium needs to offer a thermal gradient — a hot (basking) zone, usually warmed by a lamp or a heat cable/mat, and a cool zone on the opposite side — so the animal can choose, on its own, where to be based on what it needs at that moment.
The hot zone is typically used to raise body temperature before or after meals (heat speeds up digestion and lowers the risk of impaction and infection), while the cool zone is used to rest and avoid overheating. Terrariums without this gradient — with a single, uniform temperature — prevent this self-regulation and make respiratory disease, digestive problems, and weakened immunity more likely.
UVB (ultraviolet B) radiation is essential for most diurnal species because it triggers vitamin D3 production in the skin. Without enough D3, the gut can't absorb the calcium present in the diet, even when the food is well balanced — the result is metabolic bone disease (MBD), which causes deformities, spontaneous fractures, and can be fatal if not treated in time.
Not every species needs the same UVB intensity: diurnal reptiles from open habitats (bearded dragon, green iguana) need strong UVB; crepuscular, nocturnal, or dense-forest species (leopard gecko, ball python, red-footed tortoise) need much lower exposure. Because of this, the bulb type, the distance to the animal, and how long the bulb has been in use (most lose UVB output long before they "burn out") need to be adjusted for each species.
Recommended temperature and UVB by reptile species
| Species | Hot / basking zone | Cool zone (or water) | Recommended UVB |
|---|---|---|---|
| Bearded Dragon (Pogona vitticeps) | 38–46 °C | 24–28 °C | 10.0 (T5 HO) — UV Index 3–4 in the basking zone |
| Leopard Gecko (Eublepharis macularius) | 29–32 °C | 24–27 °C | 2.0–7% low intensity (T5 HO) — UV Index 0.5–1.5 |
| Green Iguana (Iguana iguana) | 35–38 °C | 27–29 °C | 10.0–12% (T5 HO) — UV Index 3–4 in the basking zone |
| Ball Python (Python regius) | 31–33 °C | 24–27 °C | Low, 5.0 (T5 HO) — UV Index 1–2 |
| Red-footed Tortoise (Chelonoidis carbonaria) | 32–35 °C | 24–28 °C | 5.0–6% (T5 HO, forest species) — UV Index 2–3 |
| Red-eared Slider (Trachemys scripta elegans) | 29–35 °C | 24–28 °C | 5.0–10.0 (T5 HO) — UV Index 3–4 over the basking dock |
Frequently asked questions
Why does my reptile need two different temperature zones?
Reptiles are ectotherms: unlike dogs and cats, they don't produce enough body heat on their own and rely on the environment to regulate their internal temperature. A terrarium with a hot (basking) zone and a cool zone lets the animal move freely between the two to reach the ideal temperature for whatever it's doing — digesting, resting, breeding, or simply keeping its metabolism running.
What is UVB and why does it matter so much?
UVB (ultraviolet B) light is the radiation band a reptile's skin uses to synthesize vitamin D3. Without enough D3, the body can't absorb calcium from the diet, even if the food is rich in the mineral — which leads to metabolic bone disease (MBD), one of the most common causes of preventable illness and death in pet reptiles.
Does every reptile need UVB at the same intensity?
No. Diurnal species from open, sunny habitats, like the bearded dragon and green iguana, need more intense UVB (UV Index 3–4 in the basking zone). Crepuscular/nocturnal species, like the leopard gecko, or dense-forest species, like the red-footed tortoise, need much lower UVB. Using a bulb that's too strong for the wrong species can cause burns and other health problems.
How do I check whether the temperature and UVB are correct?
Use a digital probe thermometer (or a thermal camera) to measure the exact temperature at the hottest point of the basking spot and the coolest point of the terrarium — analog dial thermometers tend to be inaccurate. For UVB, the best tool is a UV Index meter (such as the Solarmeter 6.5), which shows the real intensity reaching the animal, since it varies a lot with the distance from the bulb, the type of screen/lid, and how long the bulb has been in use.
Do the ideal temperature and UVB change with the reptile's age or subspecies?
Yes. Hatchlings, gravid/pregnant females, and sick animals often need fine adjustments to temperature and UVB exposure, and different subspecies or morphs (such as albino leopard geckos, which are more light-sensitive) can have needs that differ from the averages shown here. The values in this calculator are a general starting-point reference — not an individualized protocol.
Important notice
This calculator is for educational purposes and does not replace a veterinary evaluation. When in doubt, consult a veterinarian.