How to play

Each round has ten questions. Each one asks for a single number: a distance between two cities, a height or length, a year, how many people live in a country, how big a country or lake is, or how many of something there are (the keys on a piano, the bones in a skeleton). Type your best guess and lock it in. There is no timer (except the optional countdown in stream mode) and one guess per question.

How points work

Distances, heights, lengths, populations and areas are scored by how many times too big or too small your guess is, not by the plain difference. That keeps it fair across sizes: being 100 km off is great for London to Sydney and terrible for Vienna to Budapest.

points = 100 × (1 − |log₁₀(guess ÷ answer)|), never below 0

In words: a perfect guess scores 100. Guessing double or half scores 70 either way. Ten times too high or too low (or worse) scores 0. Points are rounded to whole numbers, so anything within about 1% scores the full 100.

“How many” questions

These ask for numbers that never change and that you can know exactly: the keys on a piano, the bones in a skeleton, the protons in a gold atom. Many are small, and with a small answer the ordinary rule would be too generous: if the answer is 3, guessing 2, 4 or 5 would each score 78 or more. So counts use the same ratio rule, twice as strict:

points = 100 × (1 − 2 × |log₁₀(guess ÷ answer)|), never below 0

Exactly right scores 100. Double or half scores 40 instead of 70, and about three times too many or too few scores nothing. Being one off costs more on a small number than on a big one, because it is a bigger mistake: one off when the answer is 4 is 25% off, one off when it is 206 is half a percent.

Guesses must be whole numbers. Closeness is given as “Off by 1”, “Off by 2” and so on when you are close, otherwise in percent like the other questions.

Years are scored by the gap in years:

points = 100 − |guess − answer| in years, never below 0

So 5 years off scores 95, 25 years off scores 75 and 100 or more years off scores 0. There is no year 0: 1 BC is followed by AD 1, so 44 BC to AD 44 is 87 years.

A round is worth up to 1,000 points. Skipping a question scores 0.

Closeness in words

After each guess you see how close you were in words, never as coloured squares: within half a percent, 1%, 5%, 10% or 25%; within a factor of 2, 3 or 10; or more than 10 times off. For years: exactly right, or within 1, 5, 10, 25, 50 or 100 years.

What you can type

• Plain numbers, with or without separators: 1200, 1,200, 1 200, 1.200.000.
• Decimals with a point or a comma: 12.5, 1,2 million.
• Size words and short forms: thousand/k, million/m, billion/bn, also lakh and crore. In a question answered in metres, m means metres.
• Other units are converted: 1083 ft, 3,461 miles, 0.33 km, 6 in.
• Areas are in square kilometres: 45,000, 45k km², 45000 sq km and 45 thousand all work; 17,000 sq mi, hectares and acres are converted. In an area question, m means million and a plain km is read as km².
• Counts are whole numbers: 206, or 206 bones.
• Years: 1969, AD 79, 44 BC or 44 BCE; a minus sign also means BC.

As you type, Ballpark shows how it reads your number (“Reads as 17.9 million people”), so you can fix a slip before locking in. On a phone the number keypad opens, and the × thousand, × million and × billion buttons (or BC for years) save typing zeros.

The reveal

You see the answer on a number line with your guess. For distances, sizes, populations, areas and counts the line uses a log scale, so equal steps mean equal ratios, the same way the points work. Then a comparison (“about twice as far as Paris to Rome”, “about twice the size of Switzerland”, “half the number of squares on a chessboard”), a short explanation of how the figure is defined and rounded, and its two sources. Areas also tell you how long each side of a square of the same size would be.

The daily round

Everyone gets the same ten questions each day, from at least four of the six categories and never more than three from one. The day changes at midnight UTC. Finish today’s round on its own day to add a day to your streak; your total doesn’t matter. If you start before midnight UTC, you have until 02:00 UTC to finish and still count it.

The first 74 days each bring ten questions nobody has seen in a daily before. After that, until new questions are added, each day is a new mix of earlier questions: such days are marked “repeat day”, and a question shows when it was first asked. Past days are in the archive; archive and practice rounds never change your streak.

Stream mode

Stream mode is for playing with an audience: very large text, an optional “chat, vote now” countdown before your guess locks, and room guesses. Type in up to twelve guesses from viewers or friends (a name is optional); at the reveal they appear on the number line and in a closest-first list with their points, and named players get a running total for the round. Room guesses live only on your screen: Ballpark does not connect to any chat service and stores nothing about them. There is no music.

Saving

Your round is saved in this browser after every guess. Close the tab, come back later and you continue at the same question. Nothing is sent to a server.