The Size It Up guide to judging scale
What is the Size It Up game?
Size It Up is a guess-the-size game that uses your eye instead of your memory. A round is two silhouettes on a paper board. The blue one on the left is a reference you can picture, drawn to scale. The red one is the mystery. You drag the red silhouette to move it, pull a corner to make it bigger or smaller until the pair looks right, press Lock In, and a grey ghost appears at the true size. Your score is how close your silhouette was to the ghost along the dimension that counts.
That last clause is what separates the Size It Up game from a trivia quiz. You are never asked to know that a blue whale is 25 metres long. You are asked whether it is about two school buses, and if you say two and a half, you still score well. Precision is rewarded on a curve rather than demanded exactly, which is what makes a size game playable by anyone and still hard to master.
Five rounds make a run. The pairs start close together, a giraffe beside a coconut palm, and drift apart, until the final round might set a dartboard against a llama or an apple against a hedgehog. Each round is worth up to 100 points, so a flawless run is 500. Most people's first attempt lands somewhere between 150 and 300, not because they lack facts but because the eye has a few reliable bad habits. The rest of this page is about those habits and how Size It Up is built to expose them.
If you would rather estimate with numbers than with your eye, the Fermi game is the natural partner: it asks for a figure, you reason your way there, and it scores how many times off you were.
Where "size it up" comes from
The verb came before the game. To size someone up, the phrase Size It Up is built on, is to look them over and take their measure, and the phrase has been American English since the middle of the nineteenth century, when the figurative sense of estimating a person's worth by eye attached itself to the older noun. The noun itself is older still: size reached English around 1300 from the Old French sise, a clipped form of assise, the sitting of a court that fixed quantities and portions. A size was originally something a judge decided.
Size It Up keeps the idiom honest. There is a judgment in every round, you commit to it, and then the measurement arrives to tell you how good the judgment was. Nothing about the game requires a tape measure or a search engine, and the best players are not the ones who know the most figures. They are the ones who have learned what their own eye gets wrong.
Why guessing the size of something is so hard
Visual estimation has been studied since the 1830s, and the findings are consistent enough to be called laws. Size It Up is designed around four of them, and every Size It Up round is a small experiment in at least one.
Eyes notice ratios, not amounts
Ernst Weber found that the smallest change you can detect grows in proportion to the thing changing. Add a centimetre to a coin and you notice; add a centimetre to a bus and you do not. Gustav Fechner turned that into a law in 1860: sensation tracks the logarithm of the stimulus. The practical consequence for a size comparison game is that a guess should be marked by how far off it is in proportion to the real figure, not by how many metres. Size It Up scores exactly that way, and it is why a few percent counts as a perfect round.
Everything drifts to the middle
H. L. Hollingworth described the central tendency of judgment in 1910. Shown a set of things to estimate, people pull every guess toward the middle of the set: the large ones are guessed too small, the small ones too large. In Size It Up this shows up as a reluctance to drag the corner of the silhouette past the edge of the board even when the answer lives there. If a whale already feels enormous next to a bus, the correct move is usually to make it bigger, and the zoom-out button exists for exactly that moment.
The first number sticks
Whatever size the mystery silhouette starts at in Size It Up becomes an anchor. Size It Up always starts the red silhouette at exactly the reference's size along the measured dimension, so the anchor is at least neutral, but it still exerts a pull. Experienced players decide on a direction before they touch the corner, then drag past the point that feels right and come back.
You know more sizes than you think
A 2006 study by Tretter, Jones and colleagues asked students from fifth grade to doctoral level to place objects on a scale from atoms to galaxies. Everyone, at every level, was better at relative size than absolute size, and the accurate ones carried a mental set of landmark objects they compared against. Size It Up hides the reference's measurement for this reason. You do not need the number. You need the landmark, and a giraffe, a door or a basketball is already one.
How to size anything up in four moves
There is a method for a Size It Up round, and it is the same one a surveyor uses without thinking.
1. Start from the reference, not the mystery
The reference is the only thing on the Size It Up board with a known size, so every judgment begins there. Note which dimension the dotted guide marks, because a whale is judged by its length and a tower by its height, and the label under the board says which one you are adjusting.
2. Count in references
Do not estimate the mystery in metres. In Size It Up, estimate it in references: three buses long, half a giraffe tall, a dozen credit cards wide. Counting whole units is something the eye does well, and it sidesteps the arithmetic that causes most big misses. Then pull the corner until the silhouette is that many references.
3. Check the other dimension
Every Size It Up silhouette has a height and a width. If your guess implies a bus that is taller than a house, or a mountain shorter than a tree, one of your assumptions is wrong. The second dimension is a free sanity check that most players never use.
4. Push past the comfortable answer
Now correct for the laws above, because Size It Up rewards the player who does. If the thing is big, nudge it bigger. If it is small, nudge it smaller. And when you have no idea which way to lean, lean small, because the scoring curve is kinder to undershooting than to overshooting, as the next section explains.
How Size It Up scores a guess
Every rule in the scoring follows from the perception research above.
Size It Up measures the red silhouette along its measured dimension, compares that with the true size, and works out the error as a share of the true size. A guess within 6% scores the full 100. From there the points fall along straight lines between published stops and reach zero at 160% out.
| Error | Points |
|---|---|
| 6% or better | 100 |
| 12% | 90 |
| 20% | 78 |
| 32% | 62 |
| 50% | 45 |
| 75% | 30 |
| 110% | 18 |
| 160% or worse | 0 |
Because the error is measured as a share of the true size, the curve is not symmetric. A guess of half the real figure is 50% out and scores 45. A guess of double the real figure is 100% out and scores about 21. Guessing triple is 200% out and scores nothing. In practice that means an undershoot is cheaper than an overshoot of the same ratio, which is why the advice above says to lean small when you are lost.
Each of the five rounds is worth the same 100 points, so a disaster in round one costs exactly as much as a disaster in round five, and the maximum for a run is 500. The 6% window is not arbitrary either. On a phone screen the smallest adjustment a finger can make on a corner is a few percent, so a tighter window would be scoring the touchscreen rather than the eye.
What is in the Size It Up data set
The current Size It Up set has 129 things in six groups. Thirty-seven animals run from a 4 mm garden ant to a 25 m blue whale, with a woolly mammoth and a dodo in between. Eighteen vehicles go from a kick scooter to a 400 m container ship. Twenty landmarks and playing fields include the Eiffel Tower, the Great Pyramid, an average Easter Island moai, Himeji Castle and a football pitch. Twenty-four everyday objects are the references most people can picture: a credit card, a US quarter, a queen-size bed, a 40-foot shipping container. Eighteen celestial bodies cover the planets, the large moons, Ceres, Vesta, Phobos and the nucleus of Halley's Comet. Twelve natural features range from a sunflower to Mount Everest and the Chicxulub crater.
Each Size It Up entry carries one figure, one dimension and one source. Animals use a typical adult, not the record holder. Vehicles and landmarks use the documented figure for the named thing, and the label says what was measured: the height of a tower, the length of a ship, the wingspan of a bat, the diameter of a planet. Everything is rounded to two or three significant digits because a size game played by eye does not need a fourth.
The game prefers to pair things from different groups, so you are more likely to see a giraffe beside a bus than a giraffe beside an elephant, and it uses the more familiar thing as the reference whenever one is clearly more familiar. The silhouettes are Twemoji emoji graphics flattened to a single colour, plus circles for planets and craters and rectangles for pitches, pools and containers. They are not scale drawings of the real thing. Every silhouette was checked so that its outline actually spans the dimension being measured, and both silhouettes in a round share one scale, so the comparison is honest even when the shape is a cartoon.
Daily puzzle or unlimited run
Size It Up has two ways to play and they are meant for different moods.
The daily Size It Up puzzle is dealt from the date. Everyone who opens the game on a given day sees the same five pairs in the same order, the result is saved on your device, and the share card shows five rows of red and white squares and your total without naming the pairs. It resets at midnight in your own time zone. This is the mode for group chats and for comparing eyes with someone on the other side of the world.
Unlimited runs are the Size It Up practice room. Every press of play deals five new pairs from the whole set, with no cap and no waiting. Your best run is remembered. If you want to get better at Size It Up, this is where it happens, because the laws of perception only loosen their grip with repetition and the reveal after every round is the feedback that does it.
Reading your Size It Up results
The Size It Up results screen lists every round with a bar for its points and a snapshot of the board at the moment of the reveal, so you can see your red guess beside the grey truth for each pair. Hover or tap a round to bring its snapshot up, and follow the source link to the figure the round was scored against. The direction of the miss matters more than the number. If four of five snapshots show a red silhouette smaller than its ghost, you have found the central tendency in your own eye, and the fix is simple: push big things bigger.
The Size It Up share card follows the points. Each round gets a row of five squares, and one square turns red for every 20 points, so a perfect round is five red squares and a zero is five white ones. The total out of 500 sits above the rows. Five full red rows is rare enough to be worth a screenshot.
Size It Up beyond the game
Judging scale against a known object, the whole of Size It Up in one sentence, is a skill in more jobs than it seems. Painters hold a pencil at arm's length to compare a head with a shoulder. Field geologists and forensic photographers put a scale bar in every frame because a photograph without one says nothing about size. Astronomers live with the fact that the Sun and the Moon look the same size from Earth although the Sun is about 400 times wider, because it is also about 400 times further away.
Two of the oldest illusions in perception are about exactly the judgment Size It Up asks for. The full Moon looks far bigger near the horizon than overhead, though a camera shows no difference, because of what sits beside it. And in the Ebbinghaus figure two identical circles look different sizes depending on the circles around them. Both say the same thing: size is read from context. That is why every Size It Up round gives you one reference and nothing else, and why the game works in a classroom. A teacher can run the daily puzzle on a projector, have the class vote on the corner, and use the reveal to talk about why a whale is longer than everyone thought.
For anyone who wants the long version of the same idea, the 1977 film Powers of Ten by Charles and Ray Eames, built on Kees Boeke's 1957 book Cosmic View, steps from a picnic blanket to the edge of the observable universe and back down into a proton, one factor of ten at a time. It is nine minutes long and it will change how far you drag the corner the next time you size something up.
