Peptide reconstitution calculator
Enter the vial strength, how much bacteriostatic water you are adding and the dose you want. The calculator returns the concentration, the volume to draw and — the number that matters at the syringe — how many units that is on a U-100 insulin syringe. It does arithmetic and nothing else.
Calculator
Supplied as a lyophilised powder; a 5mg vial in 2ml gives a concentration that keeps most doses inside a 0.3ml syringe.
Draw to
10units
on a U-100 insulin syringe (0.1 ml)
- Concentration
- 2.5 mg/ml
- 2500 mcg/ml
- Volume to draw
- 0.1 ml
- Doses per vial
- 20
- Syringe capacity
- 100 units
How this is calculated
concentration (mg/ml) = vial mg / water ml = 5 / 2 = 2.5 concentration (mcg/ml) = concentration mg/ml x 1000 = 2500 volume to draw (ml) = dose mcg / concentration mcg = 250 / 2500 = 0.1 insulin units = volume ml x 100 = 0.1 x 100 = 10 doses per vial = floor(water ml / volume ml) = floor(2 / 0.1) = 20 100 units = 1 ml on every U-100 insulin syringe. Barrel size changes how much it holds, never what a unit means.
Reusable pens and pen units
A reusable pen that is dialled in units uses the same scale as a U-100 insulin syringe: one unit is one hundredth of a millilitre on both. So every figure above applies unchanged when a pen is selected — the concentration, the volume and the unit count are identical, and only the maximum changes.
What the device choice decides is what fits. A pen has a highest number it will dial to, in the same way a barrel has a capacity, and a figure above that cannot be given in one go. Check your device's maximum dial against the figure before drawing, and if it does not fit, the options are a device with a higher maximum or more bacteriostatic water, which lowers the concentration so the same quantity occupies fewer units.
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Vial strength against water volume, with the units each combination gives for two reference doses. Read the concentration first: it is what every other number on the row follows from.
| Vial | Water | Concentration | 250mcg dose | 500mcg dose |
|---|---|---|---|---|
| 2 mg | 1 ml | 2 mg/ml | 12.5 units | 25 units |
| 2 mg | 2 ml | 1 mg/ml | 25 units | 50 units |
| 2 mg | 3 ml | 0.67 mg/ml | 37.5 units | 75 units |
| 2 mg | 5 ml | 0.4 mg/ml | 62.5 units | 125 units |
| 5 mg | 1 ml | 5 mg/ml | 5 units | 10 units |
| 5 mg | 2 ml | 2.5 mg/ml | 10 units | 20 units |
| 5 mg | 3 ml | 1.67 mg/ml | 15 units | 30 units |
| 5 mg | 5 ml | 1 mg/ml | 25 units | 50 units |
| 10 mg | 1 ml | 10 mg/ml | 2.5 units | 5 units |
| 10 mg | 2 ml | 5 mg/ml | 5 units | 10 units |
| 10 mg | 3 ml | 3.33 mg/ml | 7.5 units | 15 units |
| 10 mg | 5 ml | 2 mg/ml | 12.5 units | 25 units |
| 15 mg | 1 ml | 15 mg/ml | 1.7 units | 3.3 units |
| 15 mg | 2 ml | 7.5 mg/ml | 3.3 units | 6.7 units |
| 15 mg | 3 ml | 5 mg/ml | 5 units | 10 units |
| 15 mg | 5 ml | 3 mg/ml | 8.3 units | 16.7 units |
| 30 mg | 1 ml | 30 mg/ml | 0.8 units | 1.7 units |
| 30 mg | 2 ml | 15 mg/ml | 1.7 units | 3.3 units |
| 30 mg | 3 ml | 10 mg/ml | 2.5 units | 5 units |
| 30 mg | 5 ml | 6 mg/ml | 4.2 units | 8.3 units |
How reconstitution works
Most peptides are supplied as a lyophilised powder — freeze-dried, stable on a shelf, and not injectable in that state. Reconstitution is the step that dissolves the powder into a liquid, using bacteriostatic water: sterile water containing a small amount of benzyl alcohol, which lets a vial be entered more than once without the contents becoming a culture medium. Sterile water without that preservative is a single-use diluent and behaves differently once a vial has been opened.
How much water you add does not change how much drug is in the vial. A 5mg vial holds 5mg whether you dissolve it in 1ml or 5ml. What the water changes is the concentration, and concentration is what turns a dose into a distance on a syringe. At 5mg in 1ml the solution is 5000 mcg per millilitre and a 250mcg dose occupies 0.05ml; at 5mg in 5ml it is 1000 mcg per millilitre and the same 250mcg dose occupies 0.25ml. Same drug, same dose, five times the volume — and five times the units.
A unit is where that becomes practical. Insulin syringes are graduated U-100, meaning 100 units is exactly 1 millilitre. A unit is therefore one hundredth of a millilitre, on every U-100 syringe, whether the barrel holds 0.3ml, 0.5ml or 1ml. Barrel size changes how much the syringe holds and how finely you can read it; it never changes what a unit is worth. A dose that comes to 62 units will not fit in a barrel that holds 50 — the answer is a larger barrel or a weaker solution, not a different calculation.
Reconstituted vials keep far less well than sealed powder. The solution needs refrigeration, is sensitive to light, heat and agitation, and has a usable life measured in weeks rather than the months or years of the dry vial. The specific figure depends on the peptide, the diluent and how it is stored, and it comes from whoever supplied it. Where a medicine was dispensed on prescription, the pharmacy's own preparation and storage instructions are the ones that apply.
Frequently asked questions
How much bacteriostatic water should I use?
There is no single correct volume — it sets the concentration, and through that how many units you draw. More water means a lower concentration and more units for the same dose; less water means fewer units and less room for error at small doses. Most people pick a volume that puts their usual dose in the readable middle of the barrel rather than in the first two or three graduations. Where a pharmacy has given you a volume, that instruction overrides any of this.
How do I convert mcg to insulin units?
Micrograms are a quantity of drug; units are a volume on a syringe. You cannot convert between them without knowing the concentration. Divide your dose in micrograms by the concentration in mcg/ml to get the volume in millilitres, then multiply by 100. A 250mcg dose from a 2500 mcg/ml vial is 0.1ml, which is 10 units.
What does U-100 mean?
It describes the graduation scale: 100 units on the barrel equals exactly 1 millilitre. It is a property of the syringe, not of the medicine, and it is the same on a 0.3ml, 0.5ml and 1ml insulin syringe. That is why the units figure here does not change when you change the syringe size — only the capacity does.
How long does a reconstituted vial last?
Once mixed, a vial has a far shorter life than the sealed powder, and it needs refrigeration. The specific window depends on the peptide, the diluent and the storage conditions, and it is stated by whoever supplied it. Use their figure, not a general one from a calculator.
Does vial size change my dose?
No. The dose is the amount of drug itself; vial size and water volume together decide how many units that dose occupies on the syringe. A 250mcg dose is 250mcg whether it comes from a 5mg or a 10mg vial — the 10mg vial simply makes it half the volume if you use the same amount of water, and gives you twice as many doses.
What if my syringe is 0.5ml?
A 0.5ml insulin syringe holds 50 units. The arithmetic is unchanged — a unit is still one hundredth of a millilitre — but a dose above 50 units will not fit in one draw. The calculator flags that rather than hiding it, and the two ways out are a 1ml syringe or more bacteriostatic water, which lowers the concentration so the same dose occupies fewer units.
Before you use this
This tool performs arithmetic only. It does not recommend a dose, a frequency, a duration or a supplier. Many peptides discussed online are not approved by the FDA for the uses people describe. Compounded medicines are supplied on prescription and should be prepared exactly as your pharmacy instructs. Talk to a prescriber or pharmacist before preparing or administering anything.
Presets cover 10 peptides plus a custom entry. They are starting points for the arithmetic, not recommendations — the figures you enter are your own.