A 2804 and a 2204 could be roughly the same size motor depending on where they decide to measure specs from. Some measure the can at a 2804, where the same size motor as a 2204 would be measured at the stator.
There is no standard.
But there are a couple ways to tell if they are the same size. One would be to look at the dimensions as a drawing or from the list of specs, sometimes you can tell there what the stator size is. Or you could look at the weight, the 2804 and 2204 might be generally the same weight.