Apple gives you the 2.1 Amp 10 Watt charger so it won't take a day to charge your iPad due to the battery being much bigger. Most USB Hubs produce the .5 Amps even though they have an external power supply you plug into the wall.
Consequently, what amperage is iPhone charger?
The difference between either of those chargers and the 5-watt charger that comes with an iPhone will be just as dramatic. That's because the difference between the iPhone and iPad adapters is the rated amperage. An iPad charge brick is rated to handle 2.1 amps, while the smaller iPhone charger is rated for just 1 amp.
Can I charge my iPhone with a 2.1 amp charger?
It is possible, however, to deduce from the web page Apple created “Charge the battery in your iPad,” that Apple is aware of this capability and endorses it. Simply increasing the current from .5 amps (USB charging cable) or 1 amp (the bundled iPhone charger) to 2.1 amps (the iPad charger) boosts the charging speed.