| Type | Bits | Bytes |
| uint8_t | 8 bits | 1 byte |
| uint16_t | 16 bits | 2 bytes |
| uint32_t | 32 bits | 4 bytes |
| uint64_t | 64 bits | 8 bytes |
The fixed types uint8_t, uint16_t, uint32_t and uint64_t are equal respectively to (in most cases depending on the platform & compiler): unsigned char, unsigned short, unsigned int and unsigned long long.
The fixed types were introduced to be just that, fixed types independent of the platform.
h/t: http://www.badprog.com/c-type-what-are-uint8-t-uint16-t-uint32-t-and-uint64-t