I'm looking for a general use-case formula or reference that I can use to calculate the total mass flow rate of bleed air use in the environmental control system of any aircraft. I'm not looking for information on a specific aircraft - simply a general reference that can applies to all civil aircraft.
EASA and FAA engine type certificates often identify the total bleed mass flow, as a % of the engine's high pressure compressor exit flow. For example, see section 10, "Maximum permissible air bleed extraction" in this for the CFM56-7B, which shows 7 to 13%. If you assume in a civil aircraft that all the bleed air from the engine if for the ECS, you get an answer. (Or maybe you where actually looking for the total bleed mass flow).
If you can get this data from enough references, you could develop a general guideline.