Peptide dosage calculation is one of the most critical skills in working with reconstituted peptides — and one of the most commonly done incorrectly. An error in the calculation doesn't just affect one dose; it affects every dose drawn from that vial until you catch the mistake. Understanding the math behind peptide dosing eliminates systematic errors and gives you confidence in the precision of your research notes.
This guide walks through the complete calculation chain: from vial size and reconstitution volume through to the exact number of syringe units to draw for a target dose in micrograms.
The Units research documentation may need to Know
Before the math, make sure these units are clear:
- mg (milligram): 1/1000 of a gram. Peptide vials are measured in mg (typically 5mg, 10mg, 15mg).
- mcg or µg (microgram): 1/1000 of a milligram, 1/1,000,000 of a gram. Most peptide doses are expressed in mcg.
- mL (milliliter): Unit of liquid volume. Standard insulin syringes hold 0.5mL or 1mL.
- Units (on insulin syringe): U-100 insulin syringes have 100 units per mL. So 10 units = 0.10mL, 100 units = 1.0mL.
The conversion to memorize: 1mg = 1,000mcg
Step 1: Determine Your Concentration
Concentration = Total peptide (mg) ÷ Total water added (mL)
Examples:
- 5mg vial + 2mL BAC water = 2.5mg/mL
- 5mg vial + 2.5mL BAC water = 2mg/mL
- 5mg vial + 5mL BAC water = 1mg/mL
- 10mg vial + 2mL BAC water = 5mg/mL
Step 2: Convert Your Target Dose to mL
Once you know the concentration (mg/mL) and your target dose (mcg), calculate the volume in mL:
Volume (mL) = Target dose (mcg) ÷ 1000 ÷ Concentration (mg/mL)
Examples:
- Target: 250mcg | Concentration: 2mg/mL → 250 ÷ 1000 ÷ 2 = 0.125mL
- Target: 500mcg | Concentration: 5mg/mL → 500 ÷ 1000 ÷ 5 = 0.100mL
- Target: 200mcg | Concentration: 1mg/mL → 200 ÷ 1000 ÷ 1 = 0.200mL
Step 3: Convert mL to Syringe Units
Using a U-100 insulin syringe: multiply the volume in mL by 100 to get units.
Units = Volume (mL) × 100
- 0.125mL × 100 = 12.5 units
- 0.100mL × 100 = 10 units
- 0.200mL × 100 = 20 units
Note: syringe graduations are typically in 1- or 2-unit increments. If your calculated volume falls between graduation marks, round to the nearest visible mark and note the minor deviation.
Complete Worked Examples
Example 1: BPC-157, 250mcg dose from a 5mg vial
- Reconstitution: 5mg + 2mL BAC water = 2.5mg/mL
- Convert dose: 250mcg ÷ 1000 = 0.25mg
- Volume: 0.25mg ÷ 2.5mg/mL = 0.10mL
- Syringe units: 0.10mL × 100 = 10 units
Example 2: TB-500, 2.5mg dose from a 5mg vial
- Reconstitution: 5mg + 2mL BAC water = 2.5mg/mL
- Convert dose: 2.5mg (no conversion needed)
- Volume: 2.5mg ÷ 2.5mg/mL = 1.0mL
- Syringe units: 1.0mL × 100 = 100 units (full 1mL syringe)
Example 3: Ipamorelin, 100mcg dose from a 10mg vial
- Reconstitution: 10mg + 2mL BAC water = 5mg/mL
- Convert dose: 100mcg ÷ 1000 = 0.10mg
- Volume: 0.10mg ÷ 5mg/mL = 0.02mL
- Syringe units: 0.02mL × 100 = 2 units
Optimizing Your Reconstitution Volume for Dosing Convenience
The smartest approach is to choose your reconstitution volume such that your target dose corresponds to a round, easy-to-read syringe measurement. This reduces errors and makes consistent dosing much easier.
Target: dose in mcg should divide cleanly into a round number of syringe units.
For a 250mcg target dose using a 5mg vial:
- Add 2mL water → 2.5mg/mL → 250mcg = 10 units ✓ (clean)
- Add 2.5mL water → 2mg/mL → 250mcg = 12.5 units (awkward)
- Add 1mL water → 5mg/mL → 250mcg = 5 units ✓ (clean)
Plan your reconstitution volume around your target dose before adding water, not after.
Common Dosage Calculation Errors
Confusing mg and mcg
Off by 1000x. If your calculation gives you a dose volume of 100mL, you made this mistake. If your calculated syringe units come out to 0.1 units, you made this mistake in the other direction. Always verify your answer falls in a physically reasonable range (0–100 units on a 1mL syringe).
Wrong syringe type
U-100 syringes have 100 units per mL. U-50 syringes have 50 units per mL. If you use a U-50 syringe and apply the U-100 conversion, you'll draw twice the intended dose. Know your syringe calibration before calculating.
Forgetting the mL-to-units conversion
Drawing 0.10mL and drawing 10 units are the same thing on a U-100 syringe — but not on other syringes. Be explicit about units in your calculation to avoid confusion.
Reference: Quick Calculation Table
5mg vial + 2mL water (2.5mg/mL):
- 100mcg = 4 units
- 200mcg = 8 units
- 250mcg = 10 units
- 500mcg = 20 units
- 1mg = 40 units
10mg vial + 2mL water (5mg/mL):
- 100mcg = 2 units
- 250mcg = 5 units
- 500mcg = 10 units
- 1mg = 20 units
- 2.5mg = 50 units