VialMathCalculator

Math helper, not medical advice. Confirm every dose with your prescriber or pharmacist.

Reconstitution calculator

Peptide reconstitution calculator: water to mg/mL

The water you add to a powder vial sets its strength, and the strength decides how many syringe units every dose takes. Compare water volumes here before a vial is mixed and see what each one does to the syringe.

  • Any vial size
  • Compare water volumes
  • Mixing chart
  • Doses per vial
Start calculatingSee the chart

Reconstitution calculator

Your vial

The amount printed on the vial.

mL

Bacteriostatic water, in mL.

The dose your prescriber gave you. Check mg or mcg.

Syringe

Used only to show how long a vial lasts.

Draw to

—

units
on U-100

Enter the vial, the mix and the dose to see where to draw.

—mg/mL

Concentration

—mL

Volume to draw

—doses

Doses per vial

—days

Vial lasts (set frequency)

U-100 · 1 mL (100 units)

Drawn to scale
102030405060708090100

Worked example

12.5 units, step by step

The example numbers show how the math works. They are not a dose recommendation.

  1. 1A 5 mg vial mixed with 2.5 mL of water is 5 ÷ 2.5 = 2 mg/mL.
  2. 2A 250 mcg dose is 0.25 mg. 0.25 ÷ 2 = 0.125 mL.
  3. 30.125 mL × 100 = 12.5 units on a U-100 syringe.
  4. 4The vial holds 5 ÷ 0.25 = 20 full doses.

Reconstitution chart

Concentration for common vial sizes and water volumes, and how many units hold each 100 mcg. Every cell is worked out by the calculator’s own formula.

Same 10 mg vial, same 250 mcg dose, different water

+ 1 mL water

2.5units

10 mg/mL · 0.025 mL

+ 2 mL water

5units

5 mg/mL · 0.05 mL

+ 3 mL water

7.5units

3.333 mg/mL · 0.075 mL

Concentration after mixing (and units for each 100 mcg)
Vial+ 1 mL water+ 2 mL water+ 3 mL water+ 5 mL water
2 mg2 mg/mL5 u / 100 mcg1 mg/mL10 u / 100 mcg0.667 mg/mL15 u / 100 mcg0.4 mg/mL25 u / 100 mcg
5 mg5 mg/mL2 u / 100 mcg2.5 mg/mL4 u / 100 mcg1.667 mg/mL6 u / 100 mcg1 mg/mL10 u / 100 mcg
10 mg10 mg/mL1 u / 100 mcg5 mg/mL2 u / 100 mcg3.333 mg/mL3 u / 100 mcg2 mg/mL5 u / 100 mcg
15 mg15 mg/mL0.7 u / 100 mcg7.5 mg/mL1.3 u / 100 mcg5 mg/mL2 u / 100 mcg3 mg/mL3.3 u / 100 mcg
20 mg20 mg/mL0.5 u / 100 mcg10 mg/mL1 u / 100 mcg6.667 mg/mL1.5 u / 100 mcg4 mg/mL2.5 u / 100 mcg

U-100 syringe. Each cell: mg/mL, then how many units hold 100 mcg (0.1 mg). Computed by the same formula as the calculator.

01

More water, more units for the same dose

Adding water does not change how much peptide is in the vial, only how spread out it is. More water makes a weaker mix: the same dose takes more units, which is easier to measure when the dose is small. Less water makes a stronger mix: fewer units, a smaller injection volume, and less room for error on the lines.

The comparison above shows one vial and one dose with three water volumes. Whatever volume is used, write the resulting concentration on the vial so every later dose is worked out from the same number.

02

What to have written down before mixing

How a vial is mixed (how the water goes in, whether it is swirled, how long it sits) depends on the product, so follow its own instructions or ask your pharmacist. This page covers the numbers, and three of them are worth writing down.

  • The amount in the vial (mg), from the vial label.
  • The volume of water you were told to add (mL).
  • The concentration that gives (mg/mL), written on the vial together with the date it was first opened. CDC guidance is to date a multi-dose vial when it is first punctured.

Sources (checked 30 September 2026)

03

When a dose does not fit

If the calculator says a dose does not fit, the volume is larger than the syringe holds. A bigger syringe solves it. When a vial has not been mixed yet, less water also makes the volume smaller. Very small results (under 2 units) have the opposite problem, and more water makes them easier to measure. Ask your pharmacist before changing how a vial is mixed.

About this page

Who made it, and how

Made by FangFang, an independent app studio run by Fang Fang in Auckland, New Zealand.

We draft with AI assistance. Facts are checked against the primary sources linked on the page (US prescribing information and product labels on DailyMed, CDC and NLM pages), each with the date it was checked. Every number comes from the calculator’s own formula, which is covered by automated tests, including the worked example above. A person reviews the page before it is published. No doctor or pharmacist has reviewed it, which is why it sticks to arithmetic and quoted labels.

Last reviewed

FAQ

Questions

How much bacteriostatic water do I add to a 10 mg vial?

Use the volume in your product’s instructions or from your pharmacist. The math works with any volume: it only changes the strength. With 2 mL, a 10 mg vial is 5 mg/mL and a 250 mcg dose is 5 units; the chart shows other volumes.

Does adding more water change the dose?

No. The vial holds the same amount of peptide whatever you add. More water means each unit holds less, so the same dose takes more units on the syringe.

How many doses are in a vial?

Divide the vial amount by the dose. A 10 mg vial holds 40 full doses of 250 mcg. The calculator shows this as Doses per vial, and how long the vial lasts if you set how often you inject.

Can I use sterile water instead of bacteriostatic water?

They are different products. Sterile Water for Injection has no preservative and comes in single-dose containers. Bacteriostatic water contains benzyl alcohol so a vial can be used more than once. Which one a product needs is in its instructions; ask your pharmacist.

Does the calculator tell me what dose to take?

No. It only converts the dose you already have into mL and syringe units. It has no default doses and does not check whether a dose is right for you. Your prescriber or pharmacist decides the dose and how to prepare it.

Is anything I type sent or stored?

The math runs in your browser and nothing you type is sent to us. To save retyping, your last inputs are kept in this browser’s local storage; the Reset button clears them.

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