I struggle to find the original and don't have the patience to do the searching, but the UN's IAEA has been constantly keeping tabs on Iran, with Iran's consent, and they have the numbers pretty exactly. Prior to the war, IAEA inspectors counted and tested everything. If they had several more or fewer kg, the IAEA would surely know it.

see, e.g., https://www.firstpost.com/world/iranian-enriched-uranium-mostly-unharmed-by-israeli-us-strikes-says-un-nuclear-watchdog-13943617.html