Binary Numbers is a free online binary game that runs in the browser with no download and no account. A row of lamps sits in front of you with its place value printed under each one — 8, 4, 2, 1 to begin with, up to a full byte by the end. Three things get asked. Read the lamps and say what number they make. Switch lamps on until they add up to a number you are given. And, on the counting levels, switch the lamps to the next number up, which is where carrying lives: 0111 does not become 0112, it becomes 1000, because a run of ones all go out and the column to their left comes on. The place values stay printed the whole way through on purpose — hiding them would make this a memory test about powers of two instead of the idea it is actually teaching, which is that a number is the sum of the columns that are switched on. The three wrong answers on a reading round are the three real misreadings: the row read backwards, the count of lit lamps, and a single bit adrift.
How to play Binary Numbers
- Press Start. The line above the lamps says what the round wants.
- On a reading round, add up the place values printed under the lit lamps and tap that number from the four offered.
- On a building round you are given a number — tap lamps until the running sum under the rack matches it, then press Lock in.
- The line under the rack always shows your working: "8 + 4 + 1 = 13". Nothing is hidden.
- On a counting round the lamps already show a number, and you have to switch them to the next one up. That means carrying: a run of 1s at the right-hand end all go out and the next column to the left comes on.
- A wrong answer costs two and a half seconds and explains the mistake, including telling you when you have read the row backwards.
- Answer the level's quota before the clock empties to unlock the next level.
- Restart replays the same numbers; New Numbers generates a different set at the same level.
Tips
- Work from the left. Take the biggest column that still fits inside your target, switch it on, then repeat with what is left — the same method as making change.
- An odd number always has the 1 lamp lit, and an even number never does. That single check catches a lot of slips.
- Doubling is the whole pattern: 1, 2, 4, 8, 16, 32, 64, 128. If you know the doubles you know every column.
- To read a row quickly, add the biggest two lit columns first and then patch on the small ones.
- For the next number up, look at the right-hand end. Every 1 at the end turns to 0, and the first 0 you meet turns to 1.
- The largest number a row can hold is always one less than the next doubling: four lamps reach 15, eight lamps reach 255.
- If your answer is much too small, check you have not read the row backwards — the biggest column is on the left, exactly like ordinary numbers.
FAQ
Is Binary Numbers free to play?
Yes. It runs in your browser with no download, no sign-up and nothing to buy. All twelve levels are included and unlock as you clear them.
Does it convert both ways?
Yes. Some levels show the lamps and ask for the decimal number, some give the decimal number and ask you to switch the lamps, and level twelve mixes both with the counting rounds.
Are the place values shown, or do I have to know the powers of two?
They are printed under every lamp, all the way to 128. Hiding them would turn this into a memory test about powers of two rather than a lesson about place value, which is the actual idea.
Does it teach binary carrying?
Yes — levels six, eight and twelve ask for the next number up, and the rounds are generated so that they always carry. A round like 0101 to 0110 flips one lamp and teaches nothing, so those are never asked.
How big do the numbers get?
Three lamps at the start, a full eight-bit byte by level ten, so up to 255.
Are the wrong answers random numbers?
No. Each is a real misreading: the row read right-to-left, the number of lit lamps rather than their total, or a single bit out. The backwards option is left out when the row happens to read the same both ways.
Is this useful for computer science homework?
It covers the binary-to-decimal and decimal-to-binary conversions that come up first in any computing course, plus binary counting. It does not go into hexadecimal, two's complement or binary arithmetic beyond adding one.
Does it work on a phone?
Yes. The lamp row shares the width instead of wrapping, so even a full byte reads left to right in portrait, and every action is a single tap.