Bit Flip

Flip bits to build each number in binary. How many can you make in 60 seconds?

Level

4 bits8 bitsHex

Solved0

Seconds60

Best–

Make this number–

0 = 0x00 = 0b00000000

Bit Flip

Flip bits to make each number before the minute is up.

Click a bit, or press 1 to 8 (left to right), to flip it. The number under each bit is what it is worth.Tap a bit to flip it. The number under each bit is what it is worth.

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About Bit Flip

Computers store every number as bits: switches that are either 0 or 1. Each bit is worth twice the one to its right, so eight bits can make any whole number from 0 to 255. Bit Flip turns reading and writing binary into a sprint.

A number appears; flip the bits that add up to it. Get it right and the next one appears straight away. You have 60 seconds. It is a quick, satisfying way to learn binary, practise for an exam or a networking course, or warm up before writing low-level code.

How to play Bit Flip

Choose a level: 4 bits (decimal numbers from 1 to 15), 8 bits (decimal numbers from 1 to 255) or Hex (hex numbers from 0x01 to 0xff).
Press Start. A number to make appears above the row of bits.
Flip bits on by clicking or tapping them. The small number under each bit is what it is worth.
When the bits that are on add up to the target, it counts and a new number appears with every bit off again.
Make as many numbers as you can before the 60 seconds run out.

Bit Flip controls

Keyboard
Flip a bit	Number keys 1 to 8, left to right, or click it
Move between bits	Tab, then Space or Enter to flip
Pause and resume	P (Esc also pauses)
New round	N
Sound on or off	M

Touch screens
Flip a bit	Tap it
Pause or start again	Buttons above the bits

Bit Flip rules

How binary works

Bits are read from left to right, most significant first. In 8 bits the place values are 128, 64, 32, 16, 8, 4, 2 and 1. A number is the sum of the place values of the bits that are on: 173 is 128 + 32 + 8 + 4 + 1, written 10101101.

Hexadecimal

At the Hex level, targets are written in base 16, as programmers often write bytes: 0x00 to 0xFF. Each hex digit stands for four bits, so 0xAD is 1010 followed by 1101. The line under the bits always shows your current value in decimal, hex and binary.

Scoring

Each number you make scores one point. A round lasts 60 seconds and the clock stops while the game is paused, when the number is hidden. Targets are picked at random, never zero and never the same number twice in a row.

Records

Your best score and the number of rounds you have played at each level are saved in this browser on this device.

Tips and strategy

Work from the left. If the target is at least 128, the first bit must be on; take 128 away and look at the next bit.
Learn the powers of two up to 128 by heart: 1, 2, 4, 8, 16, 32, 64, 128.
For hex, convert one digit at a time: each hex digit is exactly four bits, so 0x3F is 0011 then 1111.
Odd numbers always have the last bit on.
One less than a power of two is all ones: 15 is 1111 and 255 is 11111111.

Frequently asked questions

How do you convert decimal to binary in your head?

Start from the biggest place value. If it fits into the number, turn that bit on and subtract it; otherwise leave it off. Repeat with each smaller place value until nothing is left.

What is the biggest number 8 bits can hold?

255, with every bit on: 128 + 64 + 32 + 16 + 8 + 4 + 2 + 1. In hex that is 0xFF.

Is Bit Flip good for learning?

Yes. It is the same skill used in computer science classes, networking (subnet masks) and low-level programming, practised quickly and repeatedly. Start at 4 bits and move up.