Reptile Terrarium Size Calculator

Reptile enclosure sizing depends on the species, adult size, and activity level of the animal. The enclosure must be large enough for thermoregulation (moving between warm and cool zones), exercise, and natural behavior.

General minimum enclosure rules:

• Snakes: the enclosure should be at least as long as the snake, half that in depth, and about three eighths in height. You will still see “two thirds of the snake’s length” quoted in older care sheets. Skip it. A snake that cannot stretch out fully cannot rest properly, and stretching out is most of what a resting snake does.
• Ground-dwelling lizards: length roughly 2 to 2.5 times the lizard’s total length, with depth and height each about equal to its length.
• Arboreal species: height matters more than floor space. Height at least twice the animal’s length, with the footprint about square.

There is a floor, and it is not negotiable. No adult reptile does well in anything under about 36 × 18 × 18 inches (91 × 46 × 46 cm), whatever the arithmetic says. Below that you cannot build a real warm-to-cool gradient, and without a gradient the animal cannot thermoregulate. This is why a 9-inch leopard gecko still needs a 36-inch enclosure: the requirement comes from the physics of the heat gradient, not from the size of the gecko. For arboreal species the same box stood on its end, 18 × 18 × 36, is the floor.

Recommended minimum enclosures by species:

Environmental requirements:

• Basking spot: 90–110°F (32–43°C) depending on species.
• Cool side: 70–80°F (21–27°C).
• Nighttime drop: 5–10°F (3–6°C) below daytime.
• UVB lighting: Essential for most diurnal reptiles (12–14 hours/day).
• Humidity: Varies greatly (20–80% depending on species).

Tip: Always research the specific care requirements for your species. These are minimum sizes, and larger enclosures are always better. Provide hiding spots on both the warm and cool sides of the enclosure.