Measuring charging by miles per hour is not a great method. You are getting energy in the form of kWh at a certain rate (kW) into a battery that contains kWh. If you have a 90kWh battery and you are charging at 10kW it would take 9 hours, roughly.
To be able to calculate this in miles per hour, you need to know the consumption of your particular car in wh/mile. You would then divide your charging rate in kW (a kW in 1000W) by your consumption constant and would get miles per hour. As an example (as I don't know the constant for your car) 48A at 240V is around 11kW, or 11000W. Using a 300w/mile constant would yield a speed of 36.6 miles per hour. A 250wh/mile constant would show 44miles/hour.
As you can see this varies per car model, an X consumes more than a 3 typically. So the same power from your charger will show a different "miles per hour" rate depending on the car that's plugged into it.