Hi Vishwas,
Output driving capability of an op amp is explicitly stated in datasheets. As far as i know there is no defined formula to compute for the output drive capability of op amps. It depends on the internal (output-stage bias current, architecture, drive level, etc.) and external (output voltage headroom, input overdrive, junction temp., etc.) settings.
You can refer to this mini-tutorial and this article for more details about output drive capability of op amps and driving capacitive loads.
Regards,
Jino