The RPi foundation recommends a 3A power supply for the RPi 4. However, 1.2A is reserved for the various USB peripherals (see
this). That leaves 1.8A as the maximum consumption of RPi 4 itself. This is consistent with the maximum power consumption tests that can be found on the net (see
this one for example).
In other words, RPi 4 will never use more than 1.8A and so it will happily run from a 2A power supply. But, if you start attaching cameras etc to its USB ports you may need a larger power supply.