On the floor I work on (I live in Canada, for the record), the ratio is typically 4:1. On occasion, it'll be 5:1, especially if we're short-staffed. It was especially crazy when we only had a few chemo nurses on the floor (the rest were still in training and not yet certified to administer chemo) - there were a couple of shifts where there were a lot of chemo patients on the floor and only 2 chemo nurses working, which left them each with 2-3 patients getting chemo simultaneously. I believe official complaints were made by those nurses, as it's incredibly stressful as well as dangerous for the patients.
The charge nurses are mindful of the patient assignments with chemo in them, though - they try balance the acuity of the assignment, basically. But, sometimes the floor is just very acute or we have a lot of patients getting chemo at the same time so it becomes hard during these times.