What makes a size comparison honest
A size comparison is an argument with two premises and a conclusion. When it goes wrong it is almost always because one of the premises was never stated, and the picture was doing the work the numbers should have done.
The four tests
A size comparison is honest when it passes all four of these. Most published ones pass two.
- Same axis, or the mismatch stated. Height against height, length against length, or a sentence saying which is which.
- Source named. Where the figure came from, and what it covers.
- Ratio given in figures. Not much bigger. The number.
- The picture agrees with the numbers. Nothing resized to fill a frame.
Test one: the axis
Of the 393 objects behind this game, 210 carry a height and 183 a length. Pick two at random and there is close to a one-in-two chance you are about to compare a height to a length without noticing.
The fix is not to avoid mixed comparisons, which would rule out most of the interesting ones. It is to say so. The Eiffel Tower at 330 m tall against Titanic at 269.1 m long is a ratio of 1.23 and the page says in its first paragraph that one figure is a height and the other a length. That single clause turns a misleading claim into a precise one.
Test two: the source
A figure without a provenance cannot be checked, and an unfalsifiable number is not evidence. The provenance does not have to be elaborate. It has to say what the figure covers and where it came from.
Compare two versions of the same sentence. A grizzly bear is 2.5 m tall. Or: a grizzly bear stands 2.5 m upright on its hind legs, roughly double its shoulder height on all fours. The second is the same number and a completely different claim, because it tells you what to picture.
The test in one line: could a reader who disagreed with you work out exactly where you and they differ? If the answer is no, the comparison is an assertion rather than an argument.
Test three: the ratio, in figures
Vague comparatives are where precision goes to die. Much bigger covers a factor of six and a factor of six hundred. Twice as big is often used for anything between 1.5 and 3.
Stating the number costs nothing and does two useful things. It lets the reader chain the comparison onto something else they know, and it exposes the claim to checking. A whale shark at 12.1 m against a T. rex at 12 m is 1.01, and only a stated figure could carry that: in words it is the same size, which is true and throws away the fact that one is measurably longer.
The corollary is that a ratio should be given to a sensible precision. Two decimal places below ten, one above. Quoting a ratio to four decimals when the underlying figures are averages of a variable population is false precision, and it undermines the parts of the claim that are solid.
Test four: the picture
This is the one that fails silently, because a wrong drawing looks confident.
The wrong method is to scale each silhouette to fit a box. Do that and a long low animal and a tall narrow tower both fill the frame, the ratio disappears, and the picture is decorative. The right method is to scale each shape on its measured axis, and then accept whatever the other dimension comes out as.
The cost is that some correct drawings look odd. Hubble at 13.2 m against a polar bear at 2.5 m, ratio 5.28, puts a long cylinder next to a compact animal, and the cylinder dominates the frame more than the ratio alone would suggest. That is what a true-scale drawing of those two objects looks like. Correcting it would be a lie told in pixels.
The common failures, named
The silent axis switch. Quoting a wingspan for one animal and a body length for the other, because it makes the gap look better.
The record against the average. Taking the largest individual of one species and a typical one of the other. This alone can move a ratio by half.
The undated design. Quoting a figure for an invented character without saying which version. Godzilla at 119.8 m is a 2021 design; the 1954 one was less than half that.
The unspecified unit. The length of a football pitch, where the laws allow a thirty-metre range.
The dramatic angle. A photograph taken from ground level makes a building enormous and an animal from below makes it monstrous. Neither is a measurement.
Why bother
Because a comparison that passes all four tests is reusable. The reader can chain it, quote it, argue with it, and build something else on top of it. One that fails them is a single-use impression, and it evaporates the moment anyone checks.
The four tests are also, not coincidentally, what makes a size worth publishing at all. Anyone can put two pictures side by side. The value is entirely in the parts that can be verified, which means the parts that were stated.