How good is
your sense
of scale?
A whale. A tower. A tennis ball.
You know what they look like.
But how big are they, really?
Just a different way to see the world.
The world is waiting.
Preparing your size challenge…
Find your kind of curious.
Animals
Wildly different scalesDinosaurs
A prehistoric perspectiveLandmarks
Bigger than the postcardVehicles
Planes, wheels & hullsSpace
Think beyond EarthEveryday objects
Small things. Big surprises.Geography
A world of distancesNature
Naturally enormousThree steps. A fresh perspective.
Something you know.
The green object has a real measurement. Use it as your mental ruler, and check the dimension you’re comparing.
Make it feel right.
Resize the coral silhouette. Drag, slide or use your arrow keys until its scale looks right beside the reference.
A little revelation.
Lock in your guess. See the true size, earn up to 100 points, and take a surprising comparison into your next round.
Get a better sense of scale.
How to estimate size with a better mental ruler
Build a sense of scale using familiar references, dimension labels and simple ratios. Practical tips for a visual size comparison game.
Find out more ↗Read the measurementHeight, length, width and diameter: what are you comparing?
Understand the dimensions used in size comparison games, including height, body length, width, diameter and mountain elevation.
Find out more ↗Animals in perspectiveAnimal size comparison: average, adult or maximum?
Read animal size comparisons accurately by checking adult ranges, sex, measurement axes and upper-size records.
Find out more ↗A few things you might wonder.
What is SizeGuess?
SizeGuess is a free visual size guessing game. Resize a coral silhouette beside a known reference, lock in your estimate, and discover the recorded real-world measurement. Every daily game has five rounds and a maximum of 500 points.
How does the daily challenge work?
Everyone receives the same five mixed-category comparisons for the same UTC date. A new set is generated automatically at 00:00 UTC. Your progress and completed result are saved in this browser, and completing consecutive daily sets builds your streak.
Can I play more than once a day?
Yes. Unlimited creates fresh five-round sets whenever you want. You can also practise one category, try timed Survival, or send a friend the same five-round challenge.
How are scores calculated?
Each round is worth up to 100 points. An estimate within a factor of 1.03 of the recorded size earns 100. Outside that band, the score decreases with the logarithm of your error: half and double both earn 50; a factor of four or more earns zero.
Where do the measurements come from?
Every object has a measurement note and a source link. We use museum estimates, scientific agencies, sports regulations, manufacturers and official monument operators. Animal sizes may describe large adults or upper limits; dinosaur dimensions are estimates.
Does SizeGuess work on a phone?
The game supports a touch slider, plus and minus buttons, and sideways dragging on the board. A mouse and keyboard work too. Use the slider’s arrow keys for small adjustments and Enter to lock in your guess.
Do I need an account?
No account is needed. Scores and streaks stay in local browser storage. Clearing that storage or changing browser starts a new personal history. The game does not send your guesses to a server.