18x18x24 vs 18x18x36 for a crested gecko

The comparison

The floor area row is the interesting one: it is identical. The entire difference is vertical, which for an arboreal animal is the dimension that counts.

What the extra foot actually does

1. It makes the gradient a gradient

The published targets are 82-85 F (28-29 C) at the top of the enclosure at the top and 70-75 F (21-24 C) at the bottom at the bottom. Air temperature stratifies vertically, so height is literally the mechanism that produces this gradient. Compress it into 24 inches and the difference between top and bottom narrows - which matters more for this species than most, because both ends of the range are hard limits: above 85 F sustained you risk stress and heat stroke, at or below 72 F you get lethargy, poor appetite and illness.

2. It gives the UVB lamp somewhere to go

A 12 inch Arcadia ShadeDweller 7% sits 8 to 12 inches above the basking branch, with the lamp above the mesh. Add the drainage layer, the substrate, and a branch positioned at a height the gecko will actually use, and 24 inches runs out quickly. At 36 inches you can put the branch at a sensible height and still have the published distance above it.

3. It makes planting practical

A drainage layer plus substrate takes 3 to 4 inches off the bottom before anything is planted. In a 24 inch enclosure that is a sixth of the height; in 36 inches it is a tenth.

Pick the 24 if, pick the 36 if

• Pick 18x18x24 if the gecko is a juvenile and you want an intermediate step, or you are short of vertical space in the room.
• Pick 18x18x36 if the gecko is over 12 g, or if you are buying once - which is the usual case. It is the published adult minimum and a standard commercial size.
• Pick larger if you want a planted bioactive build and can keep the enclosure under the 85 F ceiling.