TB-500 Reconstitution & Dosing Calculator: The Math Explained
A step-by-step guide to the math behind TB-500 reconstitution and dosing — how to calculate bacteriostatic water volume, units per dose, and syringe markings, with worked examples for 2mg, 5mg, and 10mg vials.
Why the Reconstitution Math Matters
TB-500 ships as a lyophilized (freeze-dried) powder that must be reconstituted with bacteriostatic water before it can be measured into a research dose. The single most common mistake reported in peptide research forums is a dosing error caused by miscalculating the concentration — drawing far too much or far too little because the relationship between vial size, water volume, and syringe units was never worked out on paper.
This guide breaks down the exact math so you can calculate any TB-500 dose reliably. It is a companion to our step-by-step reconstitution walkthrough and our dosage protocol guide — read those for the physical handling steps and protocol recommendations; read this for the numbers.
The Three Variables You Need
Every reconstitution calculation comes down to three numbers:
From these you derive the concentration (how much peptide is in each unit of liquid) and the draw volume (how far to pull the plunger on an insulin syringe).
Understanding Insulin Syringe Units
Research dosing almost always uses an insulin syringe marked in units (IU on the barrel), not milliliters. The key conversion to memorize:
So when a calculation tells you to draw "20 units," you are drawing 0.20 mL of your reconstituted solution. Everything below is expressed in these units because that is what you will actually read on the syringe.
The Core Formula
The concentration after reconstitution is:
Concentration (mcg per unit) = (Vial amount in mcg) / (Water volume in mL × 100)
And the draw volume for a target dose is:
Units to draw = Desired dose (mcg) / Concentration (mcg per unit)
A simpler way to think about it: the units you draw equal your desired dose divided by the total dose, multiplied by the total units of water you added.
Units to draw = (Desired dose / Total vial dose) × (Water volume in mL × 100)
Worked Example 1: A 5mg Vial
This is the most common TB-500 vial size. Suppose you reconstitute a 5mg (5,000 mcg) vial with 2 mL of bacteriostatic water.
Now calculate common doses:
| Desired Dose | Calculation | Draw |
|--------------|-------------|------|
| 2,000 mcg (2 mg) | 2,000 ÷ 25 | 80 units |
| 2,500 mcg (2.5 mg) | 2,500 ÷ 25 | 100 units (full syringe) |
| 1,250 mcg (1.25 mg) | 1,250 ÷ 25 | 50 units |
| 500 mcg | 500 ÷ 25 | 20 units |
With this setup, a standard 2.5mg research dose is exactly one full 100-unit insulin syringe — a clean, hard-to-misread number, which is why 2 mL is a popular diluent volume for a 5mg vial.
Worked Example 2: A 2mg Vial
For a smaller 2mg (2,000 mcg) vial reconstituted with 1 mL of bacteriostatic water:
| Desired Dose | Calculation | Draw |
|--------------|-------------|------|
| 2,000 mcg (2 mg) | 2,000 ÷ 20 | 100 units (whole vial) |
| 1,000 mcg (1 mg) | 1,000 ÷ 20 | 50 units |
| 500 mcg | 500 ÷ 20 | 25 units |
Worked Example 3: A 10mg Vial
For a larger 10mg (10,000 mcg) vial reconstituted with 2 mL of bacteriostatic water:
| Desired Dose | Calculation | Draw |
|--------------|-------------|------|
| 2,500 mcg (2.5 mg) | 2,500 ÷ 50 | 50 units |
| 2,000 mcg (2 mg) | 2,000 ÷ 50 | 40 units |
| 1,000 mcg (1 mg) | 1,000 ÷ 50 | 20 units |
Notice that a larger vial at the same water volume produces a higher concentration, so you draw fewer units for the same dose. Many researchers deliberately choose a water volume that makes their target dose land on a round number.
How to Pick Your Water Volume
There is no single "correct" amount of bacteriostatic water — the peptide amount is fixed by the vial, and adding more or less water only changes how many units you draw, not the total dose available. The goal is simply to land on syringe markings that are easy to read accurately. A few practical guidelines:
For a 5mg vial, 2 mL is the most popular choice because it makes a 2.5mg dose a clean 100-unit draw.
Quick Reference: Common Setups
| Vial | Water | Concentration | 2.5mg dose | 2mg dose |
|------|-------|---------------|-----------|----------|
| 2 mg | 1 mL | 20 mcg/unit | n/a | 100 units |
| 5 mg | 1 mL | 50 mcg/unit | 50 units | 40 units |
| 5 mg | 2 mL | 25 mcg/unit | 100 units | 80 units |
| 5 mg | 2.5 mL | 20 mcg/unit | 125 units* | 100 units |
| 10 mg | 2 mL | 50 mcg/unit | 50 units | 40 units |
*Exceeds a single 100-unit syringe — would require two draws.
Common Mistakes to Avoid
How This Fits Into a Full Protocol
The math above tells you how to measure a dose; it does not tell you how often to dose or for how long. Typical research protocols use a loading phase of roughly 2–2.5 mg twice weekly for several weeks, followed by a lower maintenance frequency. For the full schedule, frequency, and cycle-length discussion, see our dosage protocol guide, cycle length guide, and half-life and timing guide.
Frequently Asked Questions
How much bacteriostatic water should I use to reconstitute a 5mg TB-500 vial?
There is no single correct amount, because adding water changes only the concentration, not the total peptide available. 2 mL is the most popular choice for a 5mg vial because it produces a concentration of 25 mcg per unit, making a 2.5mg research dose a clean 100-unit draw on a standard insulin syringe.
How do I convert my TB-500 dose into syringe units?
Divide your desired dose (in mcg) by the concentration (in mcg per unit). The concentration equals the vial amount in mcg divided by the total units of water added, where total units = water volume in mL × 100. For example, a 5mg vial in 2 mL is 25 mcg/unit, so a 2,000 mcg dose is 2,000 ÷ 25 = 80 units.
What is the difference between units and milliliters on an insulin syringe?
On a standard U-100 insulin syringe, 100 units equals 1 mL, so 1 unit equals 0.01 mL. Research dosing is read in units off the barrel. Confusing units with milliliters is a common and serious source of dosing error.
Does using more water make TB-500 stronger or weaker?
Neither — it only changes the concentration per unit of liquid, not the total amount of peptide in the vial. More water means a lower concentration and a larger number of units drawn for the same dose; less water means a higher concentration and fewer units. The total dose available is fixed by the vial size.
What insulin syringe size is best for measuring TB-500?
A standard U-100, 0.5 mL or 1 mL insulin syringe with clear unit markings is typical. Choose a water volume so your usual dose lands on an easy-to-read marking (a multiple of 5 or 10 units) rather than a fraction of a unit, which improves measuring accuracy.
Sourcing Quality Peptides
Accurate dosing math only helps if the vial actually contains the labeled amount of peptide at the stated purity. Look for vendors that publish third-party testing, certificates of analysis, and HPLC purity above 98% so your concentration calculations reflect reality. Apollo Peptide Sciences provides independent third-party testing and full COAs on its TB-500, which matters when you are relying on the labeled milligram amount to calculate every dose.