A peptide calculator turns three numbers into a syringe reading: the peptide amount in the vial (mg), the volume of bacteriostatic water you add (mL), and your target dose (mcg). It returns the concentration in mcg per unit and the number of insulin-syringe units to draw.

Getting that conversion wrong is the most common reconstitution error, and it is pure arithmetic, so it is easy to prevent. This guide explains how a peptide calculator works, shows the formulas behind it, and walks through worked examples you can check by hand. Use it alongside the Peptide Calculator on this site.

This page covers the math and safe handling only. It does not recommend doses. Dose selection belongs to a licensed clinician or to the protocol of your own approved research.

How to Use a Peptide Calculator

You need four inputs and about thirty seconds. Follow the steps in order and compare the result with the hand check in the next section.

1. Enter the vial amount. Read the total peptide content on the label, for example 5 mg or 10 mg. Use the lyophilized (powder) amount, not a concentration.
2. Enter the diluent volume. This is how much bacteriostatic (BAC) water you plan to add, such as 1 mL or 2 mL. More water gives a weaker solution and a larger draw volume.
3. Enter the target dose. Type the dose in mcg (1 mg = 1,000 mcg). Take this number from your prescriber’s instructions or your documented protocol.
4. Pick the syringe. A standard U-100 insulin syringe holds 100 units per 1 mL, so 1 unit = 0.01 mL.
5. Read the output. The calculator shows the concentration (mcg per mL and per unit) and the units to draw.
6. Verify by hand. Re-run the formula below. If the two numbers differ, stop and recheck the inputs before you draw anything.

The Peptide Reconstitution Math

Every peptide calculator rests on three formulas. Concentration is the peptide in the vial divided by the water you add. The draw volume is your dose divided by that concentration. The units on the syringe are the draw volume times 100.

Worked example 1: 5 mg vial, 2 mL water

1. Concentration: 5 × 1000 ÷ 2 = 2,500 mcg/mL, which is 25 mcg per unit.
2. For a 250 mcg dose: 250 ÷ 2,500 = 0.1 mL.
3. Units: 0.1 × 100 = 10 units.
4. Check: 10 units × 25 mcg per unit = 250 mcg. The answer holds.

Worked example 2: 10 mg vial, 1 mL water

1. Concentration: 10 × 1000 ÷ 1 = 10,000 mcg/mL, which is 100 mcg per unit.
2. For a 500 mcg dose: 500 ÷ 10,000 = 0.05 mL, which is 5 units.

How many doses are in a vial?

Divide the vial content in mcg by the dose in mcg. A 5 mg vial holds 5,000 mcg, so a 250 mcg dose gives 20 doses. Adding more water does not change this number. It only changes how much volume each dose takes.

The numbers above are arithmetic illustrations, not dosing advice.

Peptide Reconstitution Chart (U-100 Syringe)

The more water you add, the weaker each unit and the more units you draw for the same dose. The last column uses a 250 mcg dose purely as a fixed example so the rows can be compared.

Draws under about 5 units are hard to read on a U-100 syringe, where each mark is a small fraction of a millilitre. If your result is in that range, add more water to the vial or use a 0.3 mL syringe, then recalculate.

Reconstitution, Storage and Handling Basics

Correct math only helps if the vial is prepared and stored properly. These are general handling principles. The label, certificate of analysis or prescriber instructions for your specific product always take priority.

• Use the right diluent. Bacteriostatic water contains 0.9% benzyl alcohol, which limits bacterial growth in a vial that is punctured more than once. Sterile water has no preservative and is generally treated as single-use.
• Keep it clean. Wipe the vial stopper with an alcohol swab before every puncture and use a new sterile syringe each time.
• Add water gently. Run it slowly down the inside wall of the vial instead of spraying it onto the powder.
• Swirl, do not shake. Peptides are fragile chains of amino acids, and vigorous shaking can damage them. Let the powder dissolve on its own.
• Refrigerate after mixing. Reconstituted vials are normally kept at 2 to 8 °C (36 to 46 °F) and protected from light. How long a mixed peptide stays stable varies by compound, so follow the supplier’s guidance instead of a general rule.
• Label the vial. Write the peptide name, the water volume you added and the date, so the concentration is never a guess.
• Discard anything cloudy, discoloured or contaminated.

Common Peptide Calculation Mistakes

Most reconstitution errors come from unit confusion, not from hard math. Check these before every draw.

• Mixing up mg and mcg. 1 mg is 1,000 mcg. Entering 5 instead of 5,000 changes the answer by a factor of 1,000.
• Confusing units with mL. On a U-100 syringe, 10 units is 0.1 mL, not 10 mL. Always confirm which syringe you hold, because 0.3 mL and 0.5 mL syringes label their marks differently.
• Changing the water volume after calculating. If you add 2 mL but calculated for 1 mL, every number is wrong. Calculate after you decide the volume, then label the vial.
• Forgetting a vial’s blend or strength. Some vials contain two compounds or a different total than the label name suggests. Use the actual milligrams stated on the label.
• Trusting one calculation. Run the reverse check: units drawn × mcg per unit should equal your dose.
• Rounding too early. Keep full precision until the final step, then round the units to a mark you can actually read.

Peptide Calculator FAQ