What is the difference between 433 MHz and 868 MHz, and which is better?
At the same distance, 868 MHz produces 6 dB more free-space loss than 433 MHz (71.2 dB versus 65.2 dB at 100 m) and, with a wavelength of 34.6 cm versus 69.1 cm, reaches behind obstacles more weakly. In return, the power allowed in the 868 MHz band is generally 25 mW ERP against 10 mW at 433 MHz, and the antennas are half the length (8.6 cm versus 17.3 cm).
The superiority of the two bands depends on conditions; it is not absolute.
In favour of 433 MHz: thanks to the long wavelength (69.1 cm), diffraction around obstacles such as building corners, beams and walls is more effective; there is 6 dB less path loss for the same link. Being a crowded band is its disadvantage: garage remotes, car keys and telemetry are all in the same place.
In favour of 868 MHz: the typical permitted power is 25 mW ERP (10 mW at 433 MHz), that is, an advantage of about 4 dB in power closes most of the 6 dB path loss difference. The band is relatively cleaner and the antenna is half the length, which is a serious mechanical advantage in handheld remote controls.
On the duty cycle side the balance reverses: while up to 10% transmission is allowed at 433 MHz, the limit in most sub-bands of 863–870 MHz is 1%, that is 36 seconds in total per hour. This is decisive in applications requiring a continuous stream of commands.
When deciding, compare not the band but the link budget: without calculating permitted power, antenna gain, receiver sensitivity and the field noise floor together, it cannot be said which band wins.
Full coverage of the topic: 433 MHz or 2.4 GHz?