Why published animal sizes disagree
Look up the height of a giraffe in three places and you will get three answers. The spread comes from four things, and once you can name them the disagreement stops being confusing and starts being informative.
Four reasons, and they compound
Published animal sizes vary for four reasons, and any given disagreement usually involves at least two of them at once. Naming them turns a contradiction into a set of separate, answerable questions.
- The measurement convention. Where the tape starts and stops.
- Average against maximum. Whether the figure describes a typical adult or the largest confirmed individual.
- Sex and population. Many species have males and females of very different size, and separate populations that differ again.
- The quality of the record. How many animals have actually been measured, and by whom.
The giraffe, which has all four
The figure used here is 5.3 m, and it is a height. You will find 5 m, 5.5 m and 5.7 m elsewhere, and none of those sources is careless.
The convention question is whether the horns count. A giraffe's ossicones add most of twenty centimetres and are not part of the skull in the way a horn is, so some measurements stop at the top of the head. The average-against-maximum question is worse: bulls are substantially taller than cows, and the tallest recorded bulls exceed the typical bull by close to half a metre. The population question adds another layer, because the subspecies differ.
What this means in practice is that the giraffe-to-human ratio of 3.10 used on this site would be 3.33 if you took the tallest figure in circulation. Both are defensible. Neither is a fact about giraffes so much as a fact about which giraffe.
Whale sharks are the widest spread in the set. The figure used here is 12.1 m total length. Published averages run as low as 9 m and confirmed individuals reach past 18 m. That is a factor of two between two honest sources, and it comes almost entirely from the difference between a typical adult and a record one.
Why marine animals are the worst
Large sea animals are difficult to measure and rarely measured under controlled conditions. A blue whale at 27 m is a good working figure, and lengths past 30 m have been recorded for the largest females. Sperm whales are quoted at 16 m here, with males running far larger than females. A killer whale at 7.3 m is an average adult male, and females are a couple of metres shorter.
The sex difference is the part most often dropped in popular sources. A sperm whale at 16 m against a killer whale at 7.3 m gives a ratio of 2.19. Compare a male sperm whale against a female orca and the ratio moves past three without either figure being wrong.
Conventions worth memorising
A handful of conventions explain most of the confusion people meet in practice.
Total length against standard length. Fish are measured total length, snout to the tip of the upper tail lobe. A great white shark at 4.75 m uses that convention. Squid are measured standard length, mantle and head only, with the two long feeding tentacles left out, which is why a giant squid at 4 m seems small to anyone who has seen a photograph with the tentacles extended. Counting those roughly doubles the number.
Snout to notch. Cetaceans are measured to the notch between the tail flukes rather than to the fluke tips, because the flukes are flexible and their tips are not a repeatable point.
Head and body. Big cats, capybaras and tarsiers are measured head and body with the tail excluded. A Siberian tiger quoted nose to tail includes about a metre of tail, so the two conventions differ by a third of the animal.
Standing height against upright height. This one catches people constantly. A grizzly bear at 2.5 m is standing on its hind legs. That gives a ratio of 1.46 against a person, which sounds modest until you remember the bear on all fours is roughly half that figure. Quoting the upright number and picturing the four-legged animal is the single most common bear error in print.
Extinct animals are a separate problem
Everything above assumes an animal that can be measured. For extinct species the figure is a reconstruction, and the confidence varies enormously. Megalodon at 16 m against a blue whale at 27 m puts a well-measured modern animal against one known almost entirely from teeth, with body length inferred from tooth size. Published megalodon figures run from about 15 m to over 20 m for that reason.
T. rex is in much better shape, with several substantially complete skeletons, but even there the 12 m figure is an average and the largest known individual is considerably longer. Diplodocus at 25 m depends on vertebra counts that differ between specimens, and the tail is close to half the animal.
What to do about it
Pick a convention, state it, and stay with it. That is the whole answer. The figures on this site are not more correct than the ones you will find elsewhere; they are consistent, and every page says what the number covers and which axis it belongs to.
Consistency is what makes a ratio mean anything. A blue whale at 27 m against a whale shark at 12.1 m gives 2.23, and that number holds only because both figures are total lengths of average adults taken the same way. Swap one for a record individual and the ratio moves by half. The comparison is only ever as good as the agreement between its two sides.