Can I use MacBook Pro’s charger for iPad Air.

Yes, you can use your MacBook Pro USB Power Adapter.

Whilst your iPad will not be able to charge at the full rated power output of the Power Adapter, the iPad will charge at its maximum supported rate.

USB charging/voltage standards have moved-on considerably from those of just a few years ago. Your iPad Air4, in common with most of the more recent models, supports USB Power Delivery (USB-PD).

USB-PD has a number of “profiles”. When connecting devices, the load (iPad) negotiates is power requirements with the source (Power Adapter); this negotiation matches the power needs of the load with the capabilities of the source.

Your iPad supports charging via a standard USB Power Adapter, with a USB Type-A connection, at 12W (2.4A @5V).

By contrast, when connected to a USB-PD compliant Charger, with a USB-C connection (such as your Mac Power Adapter), your iPad supports charging at 18W (1.5A @12V).

So, in conclusion, you can use your Mac Power Adapter with your iPad. Your iPad will charge at its 18W rate (1.5A @12V).

I hope this clarification and technical explanation is helpful to you.

usb-c means 5volt

watt = Volt * Amps

devices which charge pull the amount of Amps as it was build to no more

watt is a means of telling how many amps of current can be drawn of the charger before it's forced to lower the volts.

so if you find a 600Watt usb-c charger it would work as well the ipad would just not taking advantage of how much current the charger would be able to provide, sort of like if you have a stereo which can play really really loud, but you don't or a really fast car but you stay within the speed limit.

if the charger does not output higher than 5volts and the connector fit you can