What is the amplitude of infrared?

The question is not correctly phrased, Infrared is electromagnetic radiation which consists of waves. Amplitude is a measure of the maximum "strength" or height of the wave and therefore will have a whole range of values from 0 upwards. Infrared does not have a specific range of amplitude however it will have a range of frequencies ( visible light Red end 4 x 1014 Hertz - 3 x 1011 Hertz Microwaves ) and wavelength (visible light Red end 750 nanometres - 1000000 nm nanometres Microwaves)