As brokedownpalace10 said, you should probably start by measuring a higher amount, and then divide it. What he suggested is called "enhanced leaf", you can search around this place and find all the information you need.
Basically, you dissolve a high amount of 5-meo-dmt (100mg for example) in some liquid that can evaporate cleanly (IPA, Everclear, vodka... lots of alcohols basically) and soak a known amount of herbs in that liquid, and leave it there until everything dries out, while mixing periodically.
For example, if you used 1g of herbs and 100mg of 5-meo-dmt, you will end up with 1100 mg of enhanced leaf. Every 50mg of this end product will have 4.54mg of 5-meo-dmt. ---> (100/1100) * 50 = 4.54
Then, you can measure it much more precisely. As he warned, the bottom of the jar can collect some of the product that didnt stuck to the herbs, so be careful with that.