Our plan was for this to be a temporary home for our bearded dragon as we moved across the country. I knew it was a squeeze, but we have to also fit 2 adults, 3 kids, 2 dogs, 2 cats, 2 guinea pigs with suitcases in a minivan. Before ordering, I emailed Symton directly to ask how/if this container could be heated but received no reply. I took a chance and bought it anyway. That's when I saw how small it is!! We ordered the large and the measurements refer to the top of the box. It narrows down so that the bottom is smaller, taking away nearly 2 inches lengthwise and 1 inch in width from an already small enclosure. Chewy was kind enough to refund the cost, thank you!