Question: how to calculate your power bank capacity?
Answer: Total energy in such a battery in mWH will be 10000 mah x 3.7 volt = 37000 mWH. When the output is at 5 volt, the Mah capacity of this battery will be lower. The capacity of the battery while charging at 5 volt output will be 37000 mWH divided by 5V or 7400 mAH.