Peptide Reconstitution Calculator

The three measurements

Almost every mistake in peptide arithmetic comes from treating three different quantities as if they were one. Milligrams, millilitres and syringe units measure different things, and only the first is a quantity of peptide.

mg — how much peptide

Milligrams are mass. A vial labelled 10 mg contains 10 mg of lyophilised peptide whether you add 1 mL of diluent or 5 mL. Adding liquid does not create or destroy peptide, so the mass in the vial is fixed at the moment it is manufactured. Micrograms appear frequently too: 1 mg = 1,000 mcg, so 250 mcg is 0.25 mg. Entering 250 where the field expects milligrams overstates the figure by a factor of 1,000.

mL — how much liquid

Millilitres are volume. The diluent volume you add is what turns a fixed mass into a concentration: 10 mg in 2 mL is 5 mg/mL, while the same 10 mg in 1 mL is 10 mg/mL. Doubling the diluent halves the concentration and therefore doubles the volume needed to draw the same milligram figure. Volume is what you can actually see in the barrel; milligrams are not visible at all.

Syringe units — marks on a barrel

Units are a printed scale, not a quantity of peptide. Their meaning depends on the syringe's calibration. On a U-100 barrel, 100 units = 1 mL, so 1 unit = 0.01 mL. On U-50, 50 units = 1 mL. On U-40, 40 units = 1 mL. The identical 0.2 mL volume therefore reads as 20 units on U-100, 10 units on U-50 and 8 units on U-40. Unit numbers copied from one barrel to another are not interchangeable, which is why the calculator asks which scale you are reading.

How the calculator works

1. 1Enter the amount of peptide in the vial, in milligrams, exactly as printed on the label.
2. 2Enter the liquid volume used for reconstitution, in millilitres — the amount of diluent you actually added, not the vial's capacity.
3. 3Enter the desired amount as a mathematical input: the milligram figure you want converted into a volume.
4. 4Select the syringe size and, if you need unit readings, the barrel's unit scale (U-100, U-50 or U-40).
5. 5The calculator returns concentration, required volume, equivalent syringe units, how many equal portions of that size the vial theoretically contains, and what remains after the portions you have already drawn.

Results update immediately and every result shows the arithmetic that produced it, so each figure can be reproduced on paper. The calculator does not determine what amount someone should take — the desired amount is a number you supply, and the tool only converts it.

The formulas, written out

A worked example on the default values: a 10 mg vial reconstituted with 2 mL of bacteriostatic water gives 10 ÷ 2 = 5 mg/mL. Converting 1 mg at that concentration gives 1 ÷ 5 = 0.2 mL. On a U-100 barrel that is 0.2 × 100 = 20 units; on U-40 the same 0.2 mL reads 0.2 × 40 = 8 units. The vial holds 10 ÷ 1 = 10 portions of that size.

The two central formulas can be collapsed into one — volume = (desired mg × diluent mL) ÷ vial mg — but keeping concentration as a separate step makes an error visible sooner, because a concentration figure is easy to sanity-check against the label and a volume figure is not.

Common calculation mistakes

• Confusing mg with mL. "I drew 0.5" is meaningless without a unit. At 5 mg/mL, 0.5 mL is 2.5 mg; 0.5 mg is 0.1 mL. The two readings differ fivefold and both are plausible-looking numbers on the same barrel.
• Assuming syringe units are universal. Copying "10 units" from a U-100 source onto a U-40 barrel measures 0.25 mL instead of 0.1 mL — two and a half times the volume, and therefore two and a half times the peptide.
• Forgetting that concentration depends on liquid volume. A volume figure calculated for a vial reconstituted with 1 mL is wrong the moment the next vial is mixed with 2 mL. Concentration must be recalculated for every reconstitution.
• Entering the wrong vial amount. Labels sometimes state micrograms, or state a total for a multi-vial kit. Convert to milligrams before entering: 500 mcg is 0.5 mg, not 500.
• Mixing up concentration and volume. 5 mg/mL is a ratio that describes the whole vial; 0.2 mL is a measurement of one draw. Substituting one for the other in the second formula produces a number with no physical meaning.
• Rounding too early. Rounding 0.333 mL to 0.3 mL loses 10% before the unit conversion even begins, and the error compounds across the vial. The calculator carries full precision internally and rounds only for display.

Frequently asked questions

What this tool does and does not do

This page performs mathematical and unit conversions on figures you supply. It does not determine an appropriate medical dose, it does not provide treatment recommendations, and it cannot account for any individual's medical history, other medications or circumstances. Medical decisions belong with an appropriately qualified healthcare professional working from an approved product label.

Read the full medical disclaimer before using anything on this site.

Related pages

• Semaglutide reconstitution calculator — with milligram-to-microgram conversion worked through in detail.
• Tirzepatide reconstitution calculator — including a side-by-side U-100, U-50 and U-40 comparison.
• Retatrutide reconstitution calculator — concentration and volume maths for an investigational compound.
• Peptide database — every profile on the site, searchable by category and evidence grade.
• Storage and reconstitution guide — why lyophilised powder is stable, and what happens once diluent is added.
• Weight loss peptides reference — the metabolic compounds these calculators are most often used with.

Educational and mathematical content only. Nothing on this page is medical advice or a dosing recommendation.