How can QR code store so much data?

Question

Quick googling result that QR code can hold nearly 3kb (8 bit) data. But isn\'t it just using black/white dots to represent bits? If so there\'s no way that there\'s over 20,000

Answer 1

QR Code data capacity

Numeric only:      Max. 7,089 characters 
Alphanumeric:      Max. 4,296 characters 
Binary (8 bits):   Max. 2,953 bytes 
Kanji/Kana:        Max. 1,817 characters 

Version 40 is 177 x 177 and can store up to 7,089 numerics or 4,296 alpha-numerics (at lowest error correction)