The length/ size of a Bearded Dragon depends on a few things; the species, the environment and their diet/ health
Typically the male will grow larger than the female. You can measure them in 2 ways, either by body length or from tip of the tail to the tip of their mouth – as done below.
Keeping a lizard, or any animal for that matter, in a substandard and cramped enclosure is going to stunt growth as will a poor diet lacking all necessary nutrients. Figures quoted are for the maximum documented size for the species in perfect condition in the wild, captive species and cross species/ morphs may produce slightly different lengths. You can expect captive dragons realistically to grow to about 10% less than these maximums.
All lengths are measured from tip to tip and ranked in size descending order for a full grown Bearded Dragon:
- Pogona Vitticeps (Central): 60cm/ 24 inches
- Pogona Barbata (Eastern): 60cm/ 24 inches
- Pogona Minor Mitchelli (Mitchells): 45cm/ 18 inches
- Pogona Minor Minor (Dwarf): 35-45cm/ 14-18 inches
- Pogona Nullabor (Banded): 35cm/ 14 inches
- Pogona Henrylawsoni (Lawsons/ Rankins): 30cm/ 12 inches
- Pogona Minor Minima (Western): 30cm/ 12 inches
- Pogona Microlepidota (Small Scaled): 10-15cm/ 4-6 inches
Pogona Vitticeps/ Central Bearded Dragon is the most commonly bred and outside of their natural habitat in Australia this will be the most common pet dragon available, exporting any of these dragons from the wild is illegal and there are very few programs outside of Australia that breed anything but Vitticeps or Lawsons/Rankins dragons along with their associated cross, Vittikins.
So when most people are talking about the biggest Bearded Dragon in the world, likely to be a German Giant cross (a big bearded dragon), it’ll most likely be descended from Pogona Vitticeps. Since most will have been bred captively from whatever stock was exported (probably illegally!) from Australia, it’s probably a safe bet that in the wild there will be rare cases where they have grown bigger in the wild because the size of the fully grown dragon will depend on the genetics of it’s parents and the captive genetic pool will be limited (outside Australia) to produce huge genetic variations.
If you don’t know the parents sizes/ lengths then you’ll be less sure of what to expect and unless you know the breeder and they know the exact lineage you won’t be able to estimate. But to be honest this isn’t that important as you shouldn’t really care about how big the beardie will get other than to size up their enclosure if you’re a new owner, which is why I list the maximum sizes.
In case you’re a new Bearded Dragon owner and wondering how big an enclosure you need, just remember the bigger the better. The very minimum should be a floor area that is at least 4 times the maximum length of the bearded dragon size. For example, if Pogona Vitticeps is 2 foot in length then the area of the vivarium will be 8 square feet, typically 4 long by 2 foot deep. A 1 foot dragon needs 4 square feet minimum (2×2 foot).
The biggest claim for a dragon so far has been 26 inches, but this has yet to be conclusively proven e.g. tape measure and photo.