I get these caps:

https://smile.amazon.com/gp/product/B0096UU5ZU/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Use a funnel and weigh each one with a nice scale.

This is handy if doing quite a few at once.

https://www.ebay.com/itm/Cap-M-Quik-Capsule-Filling-Machine-Kit-W-or-W-O-TAMPER-Size-0-00-000-1-2-3-or-4/112290408650?hash=item1a2507a8ca:g:dEAAAOSwZ11aYMBJ&var=413322058538