Alex Steffen says,
Hey — If, like me, you are a non-Indian, find reading Indian new sources valuable (especially during this disaster), but don't really know your lakh from your crore, and find the placement of commas in Indian numbers utterly baffling, this guide to the Indian numbering system will prove helpful:
Term / Figure / No. of zeros / In words
lakh (lac) / 1,00,000/ 5 / Hundred Thousand
crore / 1,00,00,000/ 7 / Ten million
arab / 1,00,00,00,000/ 9 / 1 billion
kharab / 1,00,00,00,00,000 / 11 / 100 billion
Link to Wikipedia tutorial