Check a tank or cage against each vet and welfare source’s minimum for your pet, side by side. Pick its label, or type its length, width and height.
How many
Your tank
Your tank against each minimum
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Where the minimums come from
Each pet’s minimums come from welfare charities (RSPCA, RSPCA Australia), a vet school (the Royal Veterinary College), a vet hospital group (VCA) and, where nothing else covers a species, a vet clinic’s care sheet. For fish, OATA’s care sheets give a minimum tank in liters. When the sources disagree, the bigger minimum is the safe side.
Tank labels and real sizes
Tank labels name a volume, so two tanks with the same gallons can have different floors. Aqueon’s 20 High is 24¼ x 12½ x 16¾ in outside and its 20 Long 30¼ x 12½ x 12¾ in. Each label here has Aqueon’s own outside size. Another maker’s tank with the same label can differ, so measure it and type its size.
A typed size gives the outside box. Its volume is worked out as length x width x height (231 cubic inches to the gallon), which is more water than the tank really holds.
Cages for small pets
Small pet cages go by their measured size, so type the length, width and height; a size in meters, such as 3 m, works too. Hamsters and gerbils also live in glass tanks, so they keep the tank labels. RSPCA Australia and the MSD manual give guinea pig minimums as a floor area, so a cage can pass on area with any shape of floor.
Bird cages are checked for one bird, against the MSD manual’s and VCA’s length, width and height. For more birds, both the MSD manual and RSPCA want a bigger cage than that.
Common questions
Should I measure the tank inside or outside?
Aqueon's sizes are outside measurements, to the edges of the frame, and the checker uses them that way. The inside is a little smaller, so when a tank only just meets a minimum, leave room for that.
Can I keep two leopard geckos in a bigger tank?
RSPCA recommends keeping leopard geckos by themselves, so the checker sizes for one. The same goes for bearded dragons, crested geckos, ball pythons and corn snakes.
Why is a 20 gallon tank fine for one source and too small for another?
OATA and VCA give minimums in liters or gallons, while RSPCA and RVC give length, width and height. A 20 Long can pass a gallon minimum and still be too short or too low for a size given in inches or centimeters.
Can I check a rabbit hutch?
Yes, but RSPCA and the Rabbit Welfare Association say a hutch on its own isn't enough. Check the whole space the rabbits can reach at all times, hutch and run together, against 3 x 2 x 1 m.
Minimums come from RSPCA, RSPCA Australia, the Royal Veterinary College, VCA Animal Hospitals, OATA, small pet charities, the MSD Veterinary Manual and vet clinics’ care sheets; tank sizes from Aqueon’s own dimensions sheet. Checked against published data from Royal Veterinary College, RSPCA, VCA Animal Hospitals, MSD Veterinary Manual and OATA (plus 15 more).
See all 63 sources
RSPCA, Leopard gecko care
RSPCA, How to care for your bearded dragon
RSPCA, Caring for your crested gecko
RSPCA, How to care for a royal python
RSPCA, How to care for a corn snake
Royal Veterinary College (Beaumont Sainsbury Animal Hospital), Leopard gecko care, reviewed December 2024 (PDF)
Royal Veterinary College, Bearded dragon care, reviewed December 2024 (PDF)
Royal Veterinary College, Crested gecko care, reviewed December 2024 (PDF)
Royal Veterinary College, Royal python care, reviewed December 2024 (PDF)
Royal Veterinary College, Corn snake care, reviewed December 2024 (PDF)
Royal Veterinary College, Hognose snake care and advice, reviewed December 2022 (PDF)
VCA Animal Hospitals, Leopard geckos: care
VCA Animal Hospitals, Bearded dragons: housing
NSW Office of Environment and Heritage, Code of Practice for the Private Keeping of Reptiles (PDF)
RSPCA Australia knowledgebase, How should I care for my bearded dragon?
The Unusual Pet Vets (vet clinic, Australia), Axolotl care sheet (PDF)
The Unusual Pet Vets (vet clinic, Australia), Australian land hermit crab care sheet, Coenobita variabilis (PDF)
Yarmouth Veterinary Center (vet clinic, US), Pacman frog care sheet
Aliso Beach Animal Clinic (vet clinic, California), Hermit Crab Care Guide, medically reviewed by Bryan Hayter, DVM (last reviewed October 2026)
Zubair Khalid, DVM, MS, PhD (a vet's personal website), Hermit Crab Tank Setup: Substrate, Temperature, and Humidity Essentials (owner-supplied text, October 25, 2026)
Habitat-OS (reptile husbandry software), African Dwarf Frogs Care Sheet, August 19, 2026 (PDF handed out at NARBC shows; owner-supplied)
General care guidance from animal welfare charities, vets and makers' published sizes. It isn't veterinary advice: if your pet seems unwell or has eaten something it shouldn't, call your vet.