Ballparkle
One question a day, one number to guess. How far is the Moon? How many bones are in your body? Get into the ballpark in three tries.
- Nothing uploaded
- Formats: ≈
- Works offline
Today’s question
Loading today’s question…
Source: (opens in a new tab)
Next puzzle in 00:00:00
- Guess 1: Not used yet
- Guess 2: Not used yet
- Guess 3: Not used yet
How to work it out
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Step 1
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Show hint 1 first
Step 2
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The last step shows with the answer.
Step 3
What you type stays on this device. Nothing is uploaded.
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What is Fermi estimation?
Fermi estimation is the art of getting a good answer from rough numbers. It’s named after the physicist Enrico Fermi, who liked to ask his students questions that seem impossible without looking things up, and showed that a few sensible guesses, multiplied together, land surprisingly close.
The trick is to break a big question into small ones you can guess: how many, how often, how big. Each guess may be off, but some will be too high and others too low, so the errors tend to cancel out.
That’s why Ballparkle scores you in orders of magnitude, the powers of ten: being within twice the answer is a fine estimate, and being within ten times is already the right ballpark.
A worked example: how much water do you drink in a lifetime?
- About 2 litres a day, counting tea, coffee and other drinks.
- About 365 days a year, so roughly 700 litres a year.
- Over a lifetime of about 80 years, that’s 80 × 700 = 56,000 litres.
- So the answer is in the tens of thousands of litres: enough to fill a small swimming pool.
How to play Ballparkle
- Read today’s question: the answer is always one number, in the unit shown.
- Drag the dial or type your guess (shortcuts such as 2k, 3.5M or “2 thousand” work), then lock it in.
- The scoreboard says “higher” or “lower” and how far off you were. You have three guesses, and a guess within 10% wins at once.
- Stuck? Each hint turns over a step of the working, for 10 points.
- See the real answer count up, how to estimate it and its source, then share your result without spoilers.
Questions
When is there a new question?
Every day at midnight where you are. Everyone whose calendar shows the same date gets the same question, so you can compare results with friends anywhere.
How is my score worked out?
From your closest guess: 100 points, minus 40 for each order of magnitude you were off (a guess twice too big or too small is about 0.3 orders off). Each hint costs 10 points and each guess after the first costs 5. Your rank, from “Bullseye!” (within 10%) to “Lost in space” (more than ten times off), says how close that guess was.
What does “orders of magnitude off” mean?
How many powers of ten separate your guess from the answer. Guessing 1,000 when the answer is 10,000 is 1 order of magnitude off; guessing 20,000 is 0.3 off, since it’s twice too big. It’s the fair way to compare a guess about grains of rice with a guess about the distance to a star.
What happens to my streak if I miss a day?
Nothing. Missing one day never breaks your streak, so a busy day doesn’t cost you. Missing two days in a row starts a new streak.
Can I play the earlier questions?
Yes. Earlier days opens every past puzzle for practice. Practice rounds are kept separately, so they don’t change your streak or your stats.
Where do the answers come from?
Every answer was checked against a published source, such as a space agency, a national statistics office, a museum or an encyclopedia, and the source is linked under the answer. Some answers are averages or the best current measurement, which the working explains.
Is my score sent anywhere?
No. The game runs in your browser, and your guesses, streak and stats are kept on this device only. Nothing is sent to us or anyone else, and there’s no account to make.
Can I play without the sound, or offline?
Sound effects start switched off; turn them on with the speaker button. The game also works offline once you’ve opened it, or after choosing Use offline in the Tools menu.