Peptide Dosage Calculator: Reconstitution and Syringe Units

A peptide dosage calculator turns three numbers into one: how far to pull the plunger. Enter how much peptide is in the vial, how much water you added and the dose you want, and it tells you the mark to draw to on your syringe.

The math is simple, but it mixes milligrams, micrograms, milliliters and syringe units, and a slip of one decimal place means a dose 10 times too high or too low. Use the calculator below, then read on for how it works, a quick-reference table and how to store a mixed vial.

Peptide Dosage Calculator

Prefer a full-page version? The same tool lives at Peptide Reconstitution Calculator.

How to Use the Calculator

The calculator has two modes.

Find dose is the one most people need:

1. Peptide in vial: the strength printed on the label, in mg, mcg or IU.
2. Diluent added: how much bacteriostatic or sterile water you put in, in mL.
3. Dose per injection: the amount you want, in the same kind of unit as the vial (mg or mcg for weight, IU for IU).
4. Syringe: pick the size you’re using.

It returns the unit mark to draw to, the concentration you’ve made and how many doses the vial holds. You can also drag the plunger on the syringe to see what other marks equal.

Find diluent works backward. Enter your vial and your dose, pick a mark you’d like the dose to land on, such as 10 or 20 units, and it tells you how much water to add.

The Math Behind It

The calculator works it out in three steps.

Step 1: Work out the concentration.

Concentration = peptide in the vial ÷ water added

A 5 mg vial is 5,000 mcg. Mixed with 2 mL of water:

5,000 mcg ÷ 2 mL = 2,500 mcg per mL

Step 2: Work out how much to draw.

Volume = dose ÷ concentration

For a 250 mcg dose:

250 mcg ÷ 2,500 mcg per mL = 0.1 mL

Step 3: Convert to syringe units.

Most people measure with a U-100 insulin syringe, where 100 units equal 1 mL, so 1 unit is 0.01 mL.

0.1 mL × 100 = 10 units

So with a 5 mg vial and 2 mL of water, a 250 mcg dose is the 10-unit mark.

Quick-Reference Table

These rows show the math for common vial sizes and water volumes on a U-100 syringe. They are worked examples, not dose recommendations.

Notice how a 2-unit dose is hard to measure accurately. Adding more water would put the same dose on a bigger, easier-to-read mark.

How Much Water Should You Add?

The water you add doesn’t change how much peptide you get, only how it’s spread out. When choosing a volume:

• Make your dose land on a readable mark. Aim for a dose of at least 5 to 10 units. Very small draws, like 2 units, are easy to get wrong.
• Make it fit your syringe. A 0.3 mL syringe holds 30 units, a 0.5 mL syringe holds 50 and a 1 mL syringe holds 100. If your dose needs more than the syringe holds, use less water.
• Make it fit the vial. Most peptide vials hold about 2 to 3 mL comfortably. Check before adding more.
• Keep the numbers round. A volume that puts your dose on 10, 20 or 25 units is easier to repeat every time. The calculator’s Find diluent mode does this for you.

Peptides Labeled in IU

Some products, such as HGH and HCG, are labeled in international units (IU) instead of milligrams. The math is the same as long as both the vial and the dose are in IU. A 10 IU vial mixed with 1 mL of water holds 10 IU per mL, so 2 IU is 0.2 mL, or 20 units.

Don’t mix IU with mg or mcg without a conversion factor. For growth hormone, our HGH IU to mg converter handles that step.

Bacteriostatic Water vs Sterile Water

Both are used to dissolve peptides, but they aren’t the same.

• Bacteriostatic water contains 0.9% benzyl alcohol, a preservative that slows bacterial growth. That’s why it’s used for vials you’ll draw from more than once.
• Sterile water has no preservative. Once opened, it’s meant to be used right away.

Benzyl alcohol isn’t safe for everyone. In the early 1980s, the CDC linked it to deaths in newborns given large amounts through flush solutions, which is why bacteriostatic water carries warnings against use in neonates.

For a vial you’ll use more than once, the CDC’s injection safety guidance says an opened multi-dose vial should be dated and thrown away within 28 days, unless the manufacturer gives a different date.

Our guides to bacteriostatic water and sterile water for injection go into more detail.

How to Store Peptides

General handling guidance for research peptides:

• Before mixing: Keep the powder cold, dry and away from light. The fridge works for short periods; the freezer, around −20°C, is usually recommended for long-term storage. Follow the seller’s label if it says otherwise.
• Before opening a cold vial: Let it come to room temperature first, so moisture doesn’t condense inside.
• After mixing: Keep the vial in the fridge and use it within the time the label or your doctor gives, and no longer than 28 days for a multi-dose vial.
• Avoid repeated freezing and thawing, which can break peptides down.
• Mix gently. Let the water run down the side of the vial and swirl or roll it. Don’t shake it hard.

For the full mixing process, see our step-by-step guide on how to reconstitute peptides.

Common Mistakes

• Mixing up mg and mcg. 1 mg is 1,000 mcg. Entering 0.25 when you mean 250 mcg, or the reverse, gives a dose 1,000 times off.
• Using the wrong syringe. These calculations assume a U-100 insulin syringe. A U-40 syringe or a plain mL syringe is marked differently.
• Rounding too early. Work out the concentration before rounding, or let the calculator do it.
• Forgetting what you added. Write the water volume and date on the vial when you mix it.
• Trusting the label without checking. A 2026 analysis of research-grade peptides found wide variation in purity and in how much peptide vials actually contained. A lab report from the seller only helps if the batch number matches your vial. Our guide on how to read a peptide COA explains what to look for.

Related Tools

• Reverse Reconstitution Calculator: work out how much water to add for a target mark.
• Cost per Dose Calculator: compare vial sizes and sellers.
• HGH IU to mg Converter: convert growth hormone units.
• Peptide injection sites and how to inject peptides: technique guides.