How to Reconstitute Peptides: The Math, Step by Step

Before you start

This page covers arithmetic and record keeping. It does not cover mixing, handling, storage, or technique.

You’ll read the label, do the concentration math, convert to mL and syringe units, and write the result down. If you need the terms first, see new to the terms? what are peptides.

FDA says mix-ups can happen when mg, mL, and units get confused. Check which unit your label uses at each step in this FDA alert on dosing errors with compounded injectables (opens in a new tab).

Read the numbers on your label

Start with the vial strength. Find the mg printed on your vial label.

Look for the liquid named on the label too, and note any date printed there. If you want a closer walkthrough of the wording, see how to read a vial label.

Write down exactly what the label says. Don’t switch mg, mL, and units.

Note the liquid amount from your label or prescriber

Write down the volume in mL. Use the liquid and the volume your label or prescriber specifies.

That number is part of the concentration math. If you are comparing volumes, see how much liquid to add.

Keep the unit with the number. Just mL here.

Work out mg per mL

Divide the mg in the vial by the mL of liquid. That gives you mg per mL.

The worked example below shows the layout on paper. Read each label twice.

Write the result as mg/mL. That is your concentration.

Example numbers to show the math, not an amount to take.

• 10 mg in the vial, 2 mL of liquid added, 0.5 mg wanted per draw (500 mcg), U-100 syringe.
• Step 1: 10 mg ÷ 2 mL = 5 mg/mL.
• Step 2: 0.5 mg ÷ 5 mg/mL = 0.1 mL.
• Step 3: 0.1 mL × 100 units per mL = 10 units.
• Answer shown by the tool: 10 units · 0.1 mL.
• On paper, 10 mg ÷ 0.5 mg = 20 full draws from this vial (leftover liquid in the syringe and vial is not counted).

Turn your amount into mL and units

Take the amount from your plan and divide it by the mg per mL. That gives you the mL to line up on your syringe.

Convert mL to units only if your syringe is marked in units. On U-100 insulin syringes, 100 units equal 1 mL, according to MedlinePlus: Giving an insulin injection (opens in a new tab) and ADA: Overview of Insulin Concentration for School Nurses (opens in a new tab).

Look at the printed numbers first. Count the lines between two printed numbers on your own barrel, and let those numbers tell you the step.

Line up the tip of the plunger with the line, and follow your own syringe's instructions. If you want the mark-reading part on its own, see how to read an insulin syringe.

Example reading: On a U-100 syringe, 100 units equal 1 mL. Example reading: On a U-100 syringe, 10 units equal 0.1 mL. Example reading: On a U-100 syringe, 50 units equal 0.5 mL. These are examples of reading the marks, not an amount to take.

Write the vial down

Write the vial details where you’ll find them again. Include the date, the volume, and any expiry from the label.

A short note helps when you come back later. For label details, including storage and expiry dates, follow the label and ask your pharmacist or prescriber.

Use Save as a vial if you want to keep the vial details with your peptide tracker. Or Open the calculator to try the peptide reconstitution calculator with your own numbers.

Common label sizes

The same math works across common vial strengths. What changes is the mg on the label and the mL you enter.

If you want side by side teaching examples for common sizes, open the reconstitution chart. Read the label on your own vial, then match the math to that number.