Rules · controls · scoring
How to play Size It Up
One rule, four controls and a scoring curve that treats overestimating and underestimating identically. It takes about twenty seconds to understand and a lot longer to get good at.
The rule
Two silhouettes appear on a measuring table. The black one is the reference: it is drawn at real scale and its measured dimension — length for objects that lie down, height for objects that stand up — is labelled in metres. The white one is the target: its identity and its size are hidden. Your job is to resize it until the two match, then lock it in.
Both shapes are always drawn with one shared scale factor, so the ratio you see on screen is exactly the ratio of the assumed sizes. Nothing is faked to make the puzzle prettier — when the red outline snaps out, the difference you see is the difference you created.
Controls
| Action | Desktop | Mobile |
|---|---|---|
| Resize | Drag anywhere. The measured edge follows the pointer. | One-finger drag anywhere |
| Nudge | ← → move 1/60 of the reference. ⇧+arrow is 1/400. | +/− buttons move 1/12 of the reference |
| Pinch | Two fingers on a trackpad scale the white shape | Two-finger pinch scales the white shape |
| Lock it in | Enter | Lock button |
Scoring
Error is measured multiplicatively: error = max(guess/truth, truth/guess) - 1. Guessing 0.5× or
2× both produce an error of 100%, which is what makes the game symmetric and fair. Inside a band the score
decays continuously, so two guesses that feel different never receive the same number.
| Relative error | Score | What it feels like |
|---|---|---|
| within 2% | 100 | You know this object. |
| within 5% | 90 | Very close. |
| within 10% | 75 | The right neighbourhood. |
| within 20% | 60 | Right shape, wrong scale. |
| within 33% | 45 | A clear miss. |
| within 50% | 30 | Half again, or two thirds. |
| within 2× | 15 | Half or double. Further off falls to 0. |
Modes
- Daily — five rounds, the same five for every player on that date, with a difficulty curve from warm-up to finisher. A streak counts consecutive days completed.
- Unlimited — endless rounds, weighted away from what you have just seen.
- Categories — the same engine with a filtered object pool.
- Challenges — send a link containing your rounds and your score. Your friend plays the same rounds before seeing your result, so there are no spoilers in the link itself.
Five tips
- Compare edges along the shared axis, never areas. Area scales with the square of length.
- Count reference-lengths against the black shape rather than converting to metres in your head.
- On a phone, pinch scales the white shape. It changes your answer.
- Your first instinct is better than your fifth correction. Most overshoot happens after 20 seconds.
- Guess the object first, then its size. Recognising "that is a shipping container" beats arithmetic.