# Peptide reconstitution math, explained with examples

> How to work out concentration, draw volume and syringe units after reconstituting a vial, with the formulas, worked examples and a reference table.

Source: https://peptidetracks.com/guides/peptide-reconstitution-math
Last updated: 2026-10-08

Reconstitution math comes down to three steps: **concentration = vial strength ÷ liquid added**, **volume = dose ÷ concentration**, and **units = volume × 100** on a U-100 syringe. For a 5 mg vial with 2 mL added, a 250 mcg dose is 0.1 mL, or 10 units.

The rest of this guide walks through each step. If you would rather not do it by hand, the [reconstitution calculator](https://peptidetracks.com/tools/peptide-reconstitution-calculator) does the same arithmetic.

This is unit arithmetic, not dosing advice. The dose, the liquid and the volume to add should come from your prescriber, pharmacist or the product label.

## Step 1: get everything into the same units

Vials are labelled in milligrams (mg). Doses are often written in micrograms (mcg). Mixing the two is the most common source of a tenfold or thousandfold error.

- 1 mg = 1,000 mcg
- 0.25 mg = 250 mcg
- 2.5 mg = 2,500 mcg

Convert the dose and the vial strength to the same unit before doing anything else.

## Step 2: work out the concentration

Concentration is how much substance is in each millilitre once the liquid has been added.

**Concentration = vial strength ÷ volume of liquid added**

| Vial | Liquid added | Concentration |
| --- | --- | --- |
| 5 mg | 1 mL | 5 mg/mL (5,000 mcg/mL) |
| 5 mg | 2 mL | 2.5 mg/mL (2,500 mcg/mL) |
| 10 mg | 2 mL | 5 mg/mL (5,000 mcg/mL) |
| 10 mg | 3 mL | 3.33 mg/mL (3,333 mcg/mL) |

Adding more liquid does not change how much peptide is in the vial. It only spreads the same amount through a larger volume.

## Step 3: work out the volume for your dose

**Volume (mL) = dose ÷ concentration**

With a 2,500 mcg/mL solution and a 250 mcg dose: 250 ÷ 2,500 = 0.1 mL.

## Step 4: convert the volume to syringe units

A U-100 insulin syringe is marked in units, where 100 units = 1 mL. Each unit is 0.01 mL.

**Units = volume (mL) × 100**

So 0.1 mL is 10 units, 0.25 mL is 25 units and 0.5 mL is 50 units.

Syringe units are a measure of volume. They are not the same as international units (IU), which measure biological activity and differ for every substance. See the [glossary](https://peptidetracks.com/glossary#syringe-units) for the difference.

## A shortcut: mcg per unit

Once you know the concentration, divide it by 100 to get how many mcg each unit mark holds.

| Concentration | mcg per unit |
| --- | --- |
| 1 mg/mL | 10 mcg |
| 2 mg/mL | 20 mcg |
| 2.5 mg/mL | 25 mcg |
| 5 mg/mL | 50 mcg |

At 2.5 mg/mL each unit is 25 mcg, so 250 mcg is 10 units and 500 mcg is 20 units.

## Checking your answer

Two quick sanity checks catch most mistakes:

1. **Does it fit the syringe?** A 0.3 mL syringe holds 30 units, a 0.5 mL holds 50 and a 1 mL holds 100. A result above that means something is off, or the solution is too dilute for that syringe.
2. **Do the doses add up?** Vial strength ÷ dose gives the number of doses in the vial. Doses × volume per dose should equal the liquid you added.

If a number looks surprising, stop and confirm with a pharmacist before drawing anything.

## Keeping the result

The concentration stays the same for the life of that vial, so it is worth writing down once rather than recalculating each time. In [PepVault](https://peptidetracks.com/features/vial-inventory) you can record each vial's strength and status alongside your dose log, so the numbers are there when you need them.


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## About PepVault

PepVault is a free peptide tracker app for Android, iPhone, iPad and Mac. It keeps a personal log of doses, vial inventory, injection sites, schedules and reminders, body measurements and side effects, and exports the history as a CSV file.

- Website: https://peptidetracks.com
- Android (Google Play): https://play.google.com/store/apps/details?id=pepvault.peptide.tracker
- iPhone, iPad and Mac (App Store, listed as PeptideMate - Peptide Tracker): https://apps.apple.com/us/app/peptidemate-peptide-tracker/id6814232280

PepVault is for personal record keeping. It does not give medical advice or recommend doses.