A dinosaur’s size is reconstructed from fossil evidence. That makes a published dinosaur length different from a manufacturer’s measurement of a particular aircraft. The Natural History Museum’s directory provides consistent reference estimates for the dinosaurs in SizeGuess.
Total length includes the tail
The Tyrannosaurus rex entry measures full body length. It does not describe hip height, skull length or the height of a museum mount. An upright pose in a film can make those dimensions difficult to separate in your memory.
Long necks change the picture
A Diplodocus silhouette spreads a substantial part of its length into the neck and tail. A theropod’s silhouette has different proportions. The Diplodocus and T. rex comparison applies the same physical scale to both while preserving the schematic drawings’ proportions.
Estimates are not precision measurements
Some fossil skeletons are relatively complete; others preserve only part of an animal. Reconstructions may use related animals to fill gaps. A published reference value gives the game a reproducible answer, but it cannot remove the uncertainty in the fossil evidence.
Do not treat a score difference of a few points as a scientific claim that one reconstruction is exact. The game’s score describes how close your estimate was to the reference value selected for that entry.
Read the museum source
Each dinosaur page links to its museum entry. You can inspect the estimate and compare it with the game’s note. A named record specimen may be longer than the species estimate used here; those are different questions.
Play the dinosaur size guessing game and browse the dinosaur length library. Start with the dimension, then judge the animal’s shape.