Reconstitution
Peptide Reconstitution Calculator
The short answer
Reconstitution math is two divisions. Concentration in mg per mL is the vial strength in mg divided by the bacteriostatic water in mL. Because a U-100 insulin syringe reads 100 units to 1 mL, one unit holds a hundredth of that concentration. Enter your own vial strength and water volume below and the calculator does both divisions and shows its working.
The volume of bacteriostatic water you add sets the concentration and nothing else. It never changes how much peptide is in the vial. That one fact is why the same vial produces completely different unit counts for different people, and why both can be right.
Education only
This calculator recommends nothing. It converts numbers you type into a concentration and a unit count, and it has no opinion about what those numbers should be. The starting values are labeled examples chosen because they divide cleanly. Nothing on this page is a dose, a protocol or medical advice, and any decision about use belongs with a qualified clinician.
The calculator
Three inputs, two outputs, and the arithmetic printed underneath so you can check it by hand.
This tool computes, it does not recommend. It converts the three numbers you type into a concentration and a unit count. It does not know what you are working with, it does not set an amount, and nothing it returns is a dose or an instruction. Any decision about use belongs with a qualified clinician.
The three fields start on example values (a 10 mg vial, 2 mL of bacteriostatic water, converting 1 mg). They are placeholders chosen because they divide cleanly. Replace them with your own figures.
Concentration
5mg/mL
10 mg spread through 2 mL of bacteriostatic water.
One unit holds
0.05mg
A U-100 barrel is 100 units to 1 mL, so one unit carries a hundredth of the concentration, or 50 mcg.
1 mg on a U-100 syringe
20units
At 5 mg/mL, 1 mg works out to 20 units. The barrel is graduated in whole units, so a figure between two ticks cannot be drawn exactly. This is arithmetic, not a dose and not an instruction.
The math it just did
concentration = vial mg / bac water mL
= 10 / 2 = 5 mg/mL
units = (amount mg / vial mg) × (bac water mL × 100)
= (1 / 10) x (2 x 100) = 20 units
The two formulas, in full
Nothing here is specific to a compound. The same two lines cover every lyophilized vial and every volume.
Concentration
mg per mL = vial strength in mg / bac water in mL
A 10 mg vial in 2 mL is 5 mg per mL. The same 10 mg vial in 1 mL is 10 mg per mL. The vial still holds 10 mg in both cases.
Units on a U-100 syringe
units = (amount in mg / vial strength in mg) × (bac water in mL × 100)
A U-100 insulin syringe holds 100 units per 1 mL, which is where the 100 comes from. Put a 10 mg vial into 2 mL and the vial holds 200 units in total, each carrying 0.05 mg.
Two limits the arithmetic does not know about
A single 1 mL U-100 syringe holds 100 units, so any result above 100 is correct as arithmetic but is not one draw. And the vial has to physically hold the volume you plan to add. Check both before trusting a number.
Working it out by hand
Four steps, and the calculator above is doing exactly these. Being able to reproduce the number without the tool is the point: a calculator you cannot check is just another thing to trust.
Read the vial strength off the label
The label states the mass of lyophilized peptide in the vial, in mg. This number is fixed. Adding bacteriostatic water never changes it, which is the single most useful thing to understand about the arithmetic that follows.
Record the bacteriostatic water volume you actually added
The volume you add sets the concentration and nothing else. Use the volume you actually put in rather than the one you meant to, and write it on the vial, because nothing on the vial records it for you and every figure downstream depends on it.
Divide the vial strength by the volume to get the concentration
Concentration in mg per mL is the vial strength in mg divided by the bacteriostatic water in mL. A 10 mg vial in 2 mL is 5 mg per mL. A 10 mg vial in 1 mL is 10 mg per mL. Same vial, same peptide, different concentration.
Convert the concentration to units on a U-100 barrel
A U-100 insulin syringe reads 100 units to 1 mL, so one unit holds one hundredth of the concentration. At 5 mg per mL, one unit holds 0.05 mg. Working the other way, units equals the amount in mg divided by the vial strength in mg, multiplied by the bacteriostatic water in mL times 100.
This page is the math. The method is next door.
Mixing a vial correctly is a physical procedure: room temperature first, alcohol on both stoppers, the water down the inside of the glass, swirl rather than shake, refrigerate afterwards. None of that is arithmetic, so it lives on its own pages rather than being crammed in beside a calculator.
How to reconstitute peptides
The step-by-step method for any lyophilized vial, storage, and the catalog calculator with per-vial presets.
Read the method
How to reconstitute retatrutide
The same two formulas worked out end to end for a 20mg vial at 1 mL, 2 mL and 3 mL, with the concentration table.
See it worked out
Keep reading
The method, the units, and the reports behind the vial strengths
How to reconstitute peptides
The step-by-step method behind the math, plus the catalog calculator.
How to reconstitute retatrutide
The same arithmetic worked out for a 20mg vial at 1, 2 and 3 mL.
Units vs mg
Why the syringe reads in units and the vial reads in mg.
Peptide injection basics
What happens after the vial is mixed.
Peptide glossary
Plain definitions for bac water, lyophilized, diluent, and the rest.
Certificates of analysis
The published batch reports behind every vial strength we state.
Reconstitution calculator: FAQ
General educational information only, research-use framing, not medical advice. This calculator performs arithmetic on numbers you supply and recommends nothing. Consult a qualified professional before acting.