Reconstitution Calculator

Work out the concentration you get from a given vial size and diluent volume, and what one syringe mark is worth.

Draft — awaiting review. Not indexed.

Formula: Concentration (mg/mL) = vial amount ÷ diluent volume. Per-unit amount = concentration ÷ units per mL of the syringe.

This tool performs mathematical conversions only. It is not medical advice and does not recommend, endorse, or evaluate the safety, efficacy, or legal status of any substance. Consult a licensed healthcare provider before using any medication or peptide, and verify the legal status of any substance in your jurisdiction before use.

What this calculates

Reconstitution is the step where a freeze-dried powder becomes a liquid you can measure. The vial tells you how much solid is inside; you decide how much liquid to add; the result is a concentration. This page does that division and then translates it into the number people actually work with — how much of the substance sits behind one mark on the syringe barrel. Note what the calculator does not do: it does not know or care what is in the vial, and it will not tell you how much to draw. Both the vial amount and the diluent volume come from you.

How it works

Concentration is the amount in the vial divided by the volume of diluent added. Adding 2 mL to a 5 mg vial gives 2.5 mg per mL. The powder itself occupies a small volume once dissolved, so strictly the final volume is very slightly more than the diluent added; for the quantities involved here that difference is far below the precision a syringe can measure, so the calculation treats the diluent volume as the final volume. The per-unit figure divides the concentration by the syringe scale — 100 marks per mL on a U-100 barrel, 40 on a U-40 — because a syringe measures volume, not mass, and the mark you stop at only means something once you know the concentration behind it.

Worked example

Take a vial holding 5 mg and add 2 mL of diluent. The concentration is 5 ÷ 2 = 2.5 mg/mL, or 2,500 mcg/mL. On a U-100 syringe, one mL is 100 marks, so each mark holds 2,500 ÷ 100 = 25 mcg, and the whole 2 mL fills 200 marks. Add 1 mL instead of 2 and everything doubles: 5 mg/mL, 50 mcg per mark. The same powder, a different number on the syringe — which is the entire reason this calculation is worth doing carefully rather than from memory.

Common mistakes

The largest error available here is a factor of ten, from entering a vial amount in the wrong unit — 5 mg and 5,000 mcg are the same quantity, but 5 mcg is not. Check the unit selector against the label rather than assuming. The second is assuming a syringe is U-100 because most are; U-40 barrels exist and reading one as U-100 gets you 2.5 times what you intended. The third is changing the diluent volume later and reusing an earlier per-unit figure — every number on this page depends on the volume you actually added, so recalculate rather than remember.

Common questions

Does the powder change the final volume?

Very slightly — the dissolved solid occupies some space, so the final volume is a little more than the diluent added. At the quantities involved the difference is well below what a syringe can resolve, so this calculator treats the diluent volume as the final volume.

What does U-100 mean?

It describes the syringe, not the contents: the barrel is graduated so that 100 marks equal 1 mL. U-40 barrels are marked so 40 units equal 1 mL. The scale is printed on the syringe.