[Explainer] units are volume, mg are mass, this is the #1 error on this site
units are volume, mg are mass, this is the #1 error on this site. It comes up every few weeks and the answer has not changed. Aim the stream down the wall of the vial rather than into the cake. Reconstitution is a solubility problem, not a mixing problem, and mechanical shear does nothing helpful. Reconstituted at…
The arithmetic in full: concentration is mass over volume, so 5mg into 2mL gives 2.5mg/mL. A U-100 syringe is graduated at 100 units per millilitre, so 1mg is 1 divided by 2.5 millilitres, which is 40 units.
Correction: that gives 40 units, not what you have written. 5mg into 1mL is 5mg/mL and the division follows from there.
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If your calculation produces a fraction of a unit, the concentration is wrong for your dose. Change the water volume until the numbers land on whole units.
Disagree with the "more water is safer" framing. It is not safer, it is just a different number to divide by.
label the vial with the date as well as the concentration
aim the stream at the glass wall, not at the cake
a U-100 syringe reads 100 units to the millilitre, every time