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Peptide Math and Dosing Calculator Guide: Concentrations, IU to mcg, Syringe Markings

March 25, 2026·8 min read

Dosing errors are the most common practical mistake in peptide use. The confusion stems from mixing up units (mcg vs. mg), misreading syringe markings (units vs. mL), and performing dilution math incorrectly. This guide walks through every calculation you will need, with worked examples, so that you can set up any peptide dose accurately and confidently.

The Units You Need to Know

Milligrams (mg) and micrograms (mcg): Peptides are manufactured and labeled in milligrams (mg) but often dosed in micrograms (mcg).

  • 1 mg = 1,000 mcg
  • A "5 mg vial" of BPC-157 contains 5,000 mcg of peptide
  • A "2 mg vial" of Ipamorelin contains 2,000 mcg

Milliliters (mL): The volume of liquid you draw into the syringe. Concentration (how much peptide per unit volume) is expressed as mcg/mL or mg/mL.

IU (International Units): Some peptides — particularly those historically associated with pharmaceutical HGH — are dosed in IU. Peptides dosed in IU are less common in the research peptide space (most are mcg), but knowing the conversion is important.

Units on an insulin syringe: An insulin syringe marked "U-100" means 100 units = 1 mL. Each unit = 0.01 mL. This is a source of significant confusion — the "units" on an insulin syringe are not the same as IU of peptide. They are just volume markings.

Calculating Peptide Concentration

Concentration is the amount of peptide dissolved in a given volume of liquid.

Formula: Concentration (mcg/mL) = Total peptide (mcg) / Volume of liquid added (mL)

Example 1: 5 mg vial of BPC-157 + 2 mL bacteriostatic water

  • Total peptide = 5 mg = 5,000 mcg
  • Volume = 2 mL
  • Concentration = 5,000 / 2 = 2,500 mcg/mL

Example 2: 2 mg vial of Ipamorelin + 2 mL bacteriostatic water

  • Total peptide = 2 mg = 2,000 mcg
  • Volume = 2 mL
  • Concentration = 2,000 / 2 = 1,000 mcg/mL

Example 3: 5 mg vial + 1 mL bacteriostatic water

  • Concentration = 5,000 / 1 = 5,000 mcg/mL (a more concentrated solution)

The amount of BAC water you add is your choice. Using more water makes a more dilute solution — each syringe unit contains less peptide, so small errors in syringe reading have less impact on dose accuracy. Using less water makes a more concentrated solution — smaller injection volumes, but more precision required.

A common practical convention: add 1–2 mL to a 5 mg vial for most peptides.

Calculating the Volume to Inject

Once you know the concentration, calculate how much volume to draw:

Formula: Volume (mL) = Desired dose (mcg) / Concentration (mcg/mL)

Example 1: Desired dose 500 mcg, concentration 2,500 mcg/mL

  • Volume = 500 / 2,500 = 0.20 mL

Example 2: Desired dose 250 mcg, concentration 2,500 mcg/mL

  • Volume = 250 / 2,500 = 0.10 mL

Example 3: Desired dose 200 mcg, concentration 1,000 mcg/mL (Ipamorelin vial from above)

  • Volume = 200 / 1,000 = 0.20 mL

Reading Insulin Syringe Markings

An insulin syringe labeled U-100 has markings from 0 to 100 units. Crucially:

  • 100 units = 1 mL = 1 cc
  • 10 units = 0.10 mL
  • 5 units = 0.05 mL
  • 1 unit = 0.01 mL

To convert from mL to syringe units: Multiply the volume in mL by 100.

  • 0.20 mL × 100 = 20 units on the syringe
  • 0.10 mL × 100 = 10 units on the syringe
  • 0.05 mL × 100 = 5 units on the syringe

Complete worked example: You have Ipamorelin at 1,000 mcg/mL and want to inject 200 mcg.

  1. Volume = 200 / 1,000 = 0.20 mL
  2. Syringe units = 0.20 × 100 = 20 units
  3. Draw the plunger to the 20 unit marking on the syringe.

The IU to mcg Conversion for HGH-Related Peptides

Synthetic HGH is dosed in IU (international units). For reference, 1 IU of HGH = approximately 333 mcg (or 0.333 mg) of HGH. However, research peptides are almost universally dosed in mcg — not IU — so this conversion rarely applies.

The only scenario where IU matters for most peptide users: if comparing research peptide GH output to pharmaceutical HGH doses in clinical literature. A GH secretagogue producing a GH pulse equivalent to 1–2 IU exogenous HGH is doing meaningful work, but this comparison is approximate at best.

For practical dosing of all research peptides (Ipamorelin, BPC-157, CJC-1295, TB-500, etc.), work entirely in mcg and mL. Avoid converting to IU unless necessary.

Dilution Math for Low-Dose Peptides

Some peptides are dosed in very small amounts (20–50 mcg), making it difficult to draw an accurate volume with a standard insulin syringe. The solution is to dilute the reconstituted peptide further before drawing.

Scenario: You have a peptide reconstituted at 1,000 mcg/mL and want to dose 20 mcg.

  • Volume needed = 20 / 1,000 = 0.02 mL = 2 units on the syringe
  • Drawing 2 units accurately is difficult; small errors represent large percentage dose errors

Dilution approach: Take 0.1 mL (10 units) from the 1,000 mcg/mL vial and add 0.9 mL of BAC water to a new sterile vial.

  • New volume = 1 mL total
  • Peptide amount = 0.1 mL × 1,000 mcg/mL = 100 mcg
  • New concentration = 100 mcg / 1 mL = 100 mcg/mL
  • Volume for 20 mcg dose at 100 mcg/mL = 0.20 mL = 20 units on the syringe (much more precise)

This second-dilution approach is useful for any peptide where your target dose volume comes out to less than 5–10 syringe units.

Peptide Dose Reference Table

Common peptide doses and the syringe markings at two typical reconstitution concentrations:

| Peptide | Typical Dose | At 1,000 mcg/mL | At 2,000 mcg/mL | |---------|-------------|-----------------|-----------------| | BPC-157 | 250–500 mcg | 25–50 units | 12.5–25 units | | Ipamorelin | 200–300 mcg | 20–30 units | 10–15 units | | CJC-1295 no DAC | 200–300 mcg | 20–30 units | 10–15 units | | GHRP-2 | 100–300 mcg | 10–30 units | 5–15 units | | TB-500 | 500–1,000 mcg | 50–100 units | 25–50 units | | Tesamorelin | 1,000–2,000 mcg | 100–200 units (use 2 syringes or larger barrel) | 50–100 units | | Epithalon | 100–500 mcg | 10–50 units | 5–25 units |

Common Dosing Errors and How to Avoid Them

Confusing mg and mcg: The most dangerous error. If your target dose is 250 mcg and you accidentally inject 250 mg, that is a 1,000x overdose. Always double-check the unit on the label and in your calculation.

Reading syringe units as mL: Drawing to "20" on a U-100 syringe is 0.20 mL, not 20 mL. This one catches beginners who are not yet familiar with insulin syringe conventions.

Forgetting to account for reconstitution volume: Some peptide powders have negligible volume. Others (especially if using multiple vials or mixing) can add up. For most single-vial reconstitutions, the powder volume is negligible and can be ignored.

Using 0.5 mL syringes vs. 1 mL syringes: Both are U-100 and read the same way in units, but the smaller barrel is physically smaller. A 0.5 mL syringe goes from 0 to 50 units. Be aware of which you are using.

Frequently Asked Questions

Q: How do I know how many mg are in a vial if the label only says units? This situation is uncommon for research peptides, which are labeled in mg or mcg. If you encounter IU labeling, look up the specific peptide's IU-to-mg conversion factor in the manufacturer documentation or scientific literature.

Q: What if my calculation gives me a non-round number (like 17.3 units)? Round to the nearest whole unit. At typical doses, a difference of 0.01 mL (1 unit) is within acceptable error range for research peptide protocols.

Q: Should I add BAC water to a specific volume, or does the final volume matter? You control the final concentration by choosing how much BAC water you add. More water = lower concentration = larger volumes per dose. Less water = higher concentration = smaller volumes per dose. Neither is inherently better; choose based on what makes accurate dosing easiest for your target dose.

Q: I added too much water to my vial by accident. Can I correct this? You cannot remove water from the vial without specialized equipment. Recalculate your concentration based on the actual volume added, then recalculate the dose volume accordingly. Your doses will simply require larger syringe volumes.

Q: What if I need a dose larger than 100 units (more than 1 mL)? Use a 1 mL or 3 mL standard syringe rather than an insulin syringe, or use a lower concentration (add more BAC water per vial) to stay within the insulin syringe range. Tesamorelin at 2 mg per dose is the most common situation requiring this.

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Disclaimer: This article is for informational and educational purposes only and is not intended as medical advice. Always consult a qualified healthcare provider before starting any supplement, peptide, or health protocol. Individual results may vary.

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