Peptide Reconstitution Calculator
A free peptide dose calculator for 104 peptides. Work out your concentration, draw volume and syringe units in seconds.
How A Peptide Dose Calculator Works
A peptide dose calculator turns three numbers you already have into the one number you need at the syringe. Start with the vial strength — the total milligrams of peptide in the vial — and the amount of bacteriostatic water you add to reconstitute it. Divide the strength by the water and you get the concentration, measured in milligrams per millilitre. That single figure describes how much peptide sits in every millilitre of the mixed vial. From there, dividing your intended dose by the concentration gives the volume you need to draw, in millilitres. Because insulin syringes are marked in units rather than millilitres, the calculator multiplies that volume by 100 to show the exact unit mark on a 1 mL syringe. The arithmetic never changes; only your vial strength, water and dose do.
The Math, Written Out
Concentration (mg/mL) = vial strength (mg) / bacteriostatic water (mL)
Volume (mL) = dose (mg) / concentration (mg/mL)
Syringe units = volume (mL) × 100
Two Worked Examples
These are arithmetic examples, not dose recommendations.
Example one. A 20 mg vial reconstituted with 2 mL of bacteriostatic water gives a concentration of 10 mg/mL. Drawing a 1 mg dose from that vial is 0.1 mL, which is 10 units on a 1 mL insulin syringe.
Example two. A 10 mg vial reconstituted with 2 mL of water gives 5 mg/mL. A 250 mcg dose from that vial is 0.05 mL, which is 5 units on the same syringe.
Common Concentrations At A Glance
Reconstitution arithmetic for reference only — not dose recommendations.
| Vial Strength | Water Added | Concentration | What One Unit Holds |
|---|---|---|---|
| 5 mg | 1 mL | 5 mg/mL | 50 mcg |
| 5 mg | 2 mL | 2.5 mg/mL | 25 mcg |
| 10 mg | 1 mL | 10 mg/mL | 100 mcg |
| 10 mg | 2 mL | 5 mg/mL | 50 mcg |
| 20 mg | 2 mL | 10 mg/mL | 100 mcg |
| 20 mg | 3 mL | 6.67 mg/mL | ≈ 66.7 mcg |
| 30 mg | 2 mL | 15 mg/mL | 150 mcg |
| 30 mg | 3 mL | 10 mg/mL | 100 mcg |
| 40 mg | 2 mL | 20 mg/mL | 200 mcg |
| 40 mg | 4 mL | 10 mg/mL | 100 mcg |
“What one unit holds” is the amount in 0.01 mL (one unit on a 1 mL, U-100 insulin syringe) at that concentration.
Questions People Ask
How Much Bacteriostatic Water Should I Add?
There is no single correct amount. More water makes the solution easier to measure but does not change the total peptide in the vial. Many people add between 1 and 3 mL. Pick a volume that puts your dose at an easy-to-read number of units, then keep it consistent for that vial.
How Do I Convert Milligrams To Syringe Units?
First find the concentration: divide the vial strength in milligrams by the millilitres of water you added. Divide your dose by that concentration to get the volume in millilitres, then multiply by 100. On a 1 mL insulin syringe, that number is the units mark you draw to.
What Does One Unit On An Insulin Syringe Hold?
On a standard 1 mL, U-100 insulin syringe, one unit is one hundredth of a millilitre, or 0.01 mL. How much peptide that 0.01 mL contains depends entirely on your concentration, so the same unit mark holds a different amount after every reconstitution.
Why Does The Same Dose Need A Different Draw On Different Vials?
Because the concentration changes. A larger vial, or the same vial with less water, is more concentrated, so a given dose sits in a smaller volume and fewer units. Reconstitute two vials differently and an identical milligram dose can land on two different unit marks.
Does More Water Make The Peptide Weaker?
No. The vial holds the same total peptide however much water you add. More water only spreads that peptide through a larger volume, lowering the concentration. Each draw then contains less peptide per unit, so you draw to a higher unit mark to reach the same dose.
How Long Does A Vial Last Once It Is Mixed?
That depends on the peptide, the concentration and storage. Reconstituted peptides are generally kept refrigerated and used within a few weeks, but the beyond-use window varies by compound. Check the guidance on each peptide protocol page rather than assuming one figure fits every vial.