There's a formula on calculating mah capacity. You can try searching online.
Battery voltage 3.4v, output at 5v, capacity loss may occur because this. Input and output affects some power loss also, 3G, apps, phone battery capacity and chipset used, standby, etc. And battery capacity is usually calculated 75-85% of stated capacity. The same applies to other power bank: 11200 mah should have around 9000mah, 5400 at 4000mah and 13000 at around 10000mah.

Just to cut short, it should have around 18650mah after conversion, able to charge an iPhone 4 for more than 10times. I personally tested on my phone with 2400mah battery, able to charge it for 8times.