How big should a gerbil cage be?

100cm long by 50cm wide by 50cm high for two gerbils, and 120 x 50 x 50cm for three. That is Woodgreen Pets Charity's published minimum, and in inches it is 39.4 x 19.7 x 19.7 for a pair, or 775 square inches of floor. Two things make that figure harder to shop for than the equivalent hamster number, which happens to be identical. The first is that it is stated for a pair rather than a single animal, because the RSPCA says gerbils should not be kept alone — so 775 square inches houses two gerbils where it houses one hamster. The second is the height: 50cm exists so that an animal can dig down 20 to 30cm and still stand fully upright above ground, and the RSPCA puts an adult gerbil at about 12cm tall. Most enclosures sold at the right floor area are nowhere near 50cm deep.

The ranked product version of this decision is the best gerbil cages. This page is the figure itself: where it comes from, what it means in the units you will actually be shopping in, how it scales with the number of animals, and why the published guidance rules out an entire category of product that would otherwise be the obvious answer.

The figure in the units on the box

The substrate column is the part that catches people out, and it is why the best gerbil bedding exists as a separate page: the first fill of a minimum-sized gerbil enclosure at the published depth is 100 to 125 liters, which is more than the largest single pack any brand on sale holds. The enclosure price is not the setup price.

Why the 50cm height is a real specification

Run the arithmetic the RSPCA's two figures imply. Substrate at 20 to 30cm, an adult gerbil about 12cm tall, and the animal needs to be able to emerge from a burrow and stand upright above the surface. 30cm of substrate plus 12cm of gerbil is 42cm before you allow any clearance at all, which is exactly why the published enclosure height is 50cm and not 40. An enclosure with a 775 square inch floor and a 25cm wall is not a compliant gerbil enclosure filled to the published depth — it is a compliant gerbil enclosure with four inches of substrate in it, which is a different thing.

This is the single most useful consequence of the figure for a shopper: measure the wall height before you measure anything else. Of the four enclosures we would consider, the deciding specification is not floor area, which several clear comfortably, but how much substrate the walls will actually retain.

What the figure rules out, and it is most of the aisle

Woodgreen advises against wire cages for gerbils, and against the mesh and solid shelves fitted to ready-made enclosures. The RSPCA goes further and asks for solid glass walls with a secure wire-mesh top and a solid floor, advising against bar cages on the basis that gerbils may injure their legs or damage their teeth on them. Both charities are describing the same product category and ruling it out, which means the gerbil answer is a tank, a display cabinet or a solid-walled enclosure — and Woodgreen says plainly that suitable gerbil housing is very limited and can be tricky to find.

Tank sizes, since the guidance points at glass

So the smallest standard aquarium that clears the published gerbil floor is a 75 gallon, and the 40 gallon breeder that gets recommended constantly is 16 percent short. A 40 breeder is not a disaster and it is not compliant, and we would rather say which it is than call it big enough.

How to measure what you are looking at

1. 1.Measure the inside of the base. External footprints on wooden and MDF enclosures include wall thickness, which on a 20mm carcass is nearly an inch and a half of width lost per side.
2. 2.Measure the wall height above the floor, not the overall height. A mesh lid frame, a sloped roof or a glass front that stops short all reduce what the enclosure will hold.
3. 3.Count one level. Woodgreen advises against the mesh and solid shelves fitted to ready-made enclosures in any case, so shelf area was never going to count towards the figure.
4. 4.Check the lid aperture. 1cm welded mesh is the figure Woodgreen gives for a homemade lid. A gerbil is a better climber than its body shape suggests.
5. 5.Then check the substrate bill. Floor area multiplied by 20cm, divided by 1,000, gives liters. For a minimum-sized enclosure that is 100 liters, and it is a real cost.

If you are still deciding between species rather than between enclosures, gerbil versus hamster is the comparison that matters here, because the two share this floor figure and it means completely different things for each.