Official website documents:
My understanding:
rpx is an adaptive unit
Calculation:
1rpx = device screen width / 750
Note: 750 is the official website regulations
Why choose iPhone6 as standard, as development simulation?
Because in iPhone6, 1px = 0.5px, which is very convenient for the conversion of px and rpx, the calculation relationship of multiplying by 2 or dividing by 2.