Each normal SizeGuess set contains five comparisons. Every round can earn 100 points, giving a maximum total of 500. Each round has the same weight; the order does not change how much it is worth.
Start with a multiplicative error
Divide your estimate by the recorded size, then consider whichever ratio is larger: that value or its reciprocal. A guess of twice the answer has an error factor of two. A guess of half the answer has the same error factor.
This approach treats equivalent proportional errors equally, whether the object is a tiny ball or a large planet. An error in centimetres alone would unfairly favour smaller objects.
The close-enough band
An error factor of 1.03 or less earns 100. Outside that band, SizeGuess calculates 100 × (1 − log(error factor) ÷ log(4)), rounds to the nearest whole point, and limits the result to 0–99. An error factor of four or more earns zero.
| Guess relative to true size | Round score |
|---|---|
| Exactly the recorded size | 100 |
| 1.03 times the recorded size | 100 |
| 1.5 times, or two-thirds | 71 |
| Double, or half | 50 |
| Four times, or one-quarter | 0 |
Survival adds time and lives
In Survival, you have three lives and 20 seconds for each round. A score below 60 costs one life. Running out of time scores zero and also costs a life. The timer uses elapsed clock time, so switching tabs does not pause the round.
Your stats are personal
Completed sets, best scores and daily streaks are saved in your browser. SizeGuess does not invent a worldwide percentile or ranking. Sharing a challenge lets friends play the same comparisons and compare their own results.
See the full methodology or try the daily five.