A peptide dosage calculator helps you turn the milligram amount on a vial into the actual milliliters or insulin units you draw into a syringe. Get this calculation wrong and you either underdose by 75% (the most common mistake) or overdose dangerously. The math is simple once you internalize it: vial mg ÷ bacteriostatic water mL = mg per mL concentration; desired dose mg ÷ concentration = mL to inject; mL × 100 = insulin units. This guide walks through the calculation step by step, gives you ready-to-use tables for the most common peptides, and explains the three mistakes that account for nearly all dosing errors.
If you have ever wondered why your peptide is “not working” after 3 to 4 weeks of dosing, the calculation is the first place to check. We get the same support call dozens of times: a customer drew 10 units of a vial that should have been dosed at 25 units. They were taking 40% of their intended dose for the entire cycle.
The Three-Step Peptide Dosage Calculation
Step 1: Calculate concentration (mg per mL)
Formula: peptide mg in vial ÷ bacteriostatic water mL added = mg/mL
Example: 5 mg vial + 2.5 mL bac water = 5 ÷ 2.5 = 2 mg/mL
This is the concentration of your reconstituted solution. Every mL contains 2 mg of peptide. Every 0.1 mL contains 0.2 mg (200 mcg).
Step 2: Calculate volume per dose (mL)
Formula: desired dose mg ÷ concentration mg/mL = mL to inject
Example: want 250 mcg (0.25 mg) at 2 mg/mL = 0.25 ÷ 2 = 0.125 mL
So your daily dose is 0.125 mL of the reconstituted solution.
Step 3: Convert mL to insulin units (for insulin syringes)
Formula: mL × 100 = insulin units
Example: 0.125 mL × 100 = 12.5 units. Draw to the 12 to 13 unit mark on an insulin syringe.
Insulin syringes are calibrated so that 1 unit = 0.01 mL. See our sub-Q vs IM guide for matching injection route to peptide type. This is why insulin syringes are the standard for peptide research; the unit markings give you precise increments without decimal math at the moment of injection.
Common Peptide Dosing Tables (Pre-Calculated)
The most common reconstitution + dose combinations:
BPC-157 (5 mg vial)
| Bac water added | Concentration | 250 mcg dose | 500 mcg dose |
|---|---|---|---|
| 2 mL | 2.5 mg/mL | 0.10 mL (10 units) | 0.20 mL (20 units) |
| 2.5 mL | 2 mg/mL | 0.125 mL (12-13 units) | 0.25 mL (25 units) |
| 5 mL | 1 mg/mL | 0.25 mL (25 units) | 0.50 mL (50 units) |
TB-500 (5 mg vial)
| Bac water added | Concentration | 2 mg dose | 2.5 mg dose |
|---|---|---|---|
| 2.5 mL | 2 mg/mL | 1.0 mL (100 units) | 1.25 mL (use 1 mL syringe) |
| 5 mL | 1 mg/mL | 2.0 mL (use 1 mL syringe x2) | 2.5 mL |
CJC-1295 + Ipamorelin (5 mg vials each)
| Vial | Bac water | Concentration | Daily dose | Volume |
|---|---|---|---|---|
| CJC-1295 5 mg | 2.5 mL | 2 mg/mL | 100 mcg | 0.05 mL (5 units) |
| Ipamorelin 5 mg | 2.5 mL | 2 mg/mL | 250 mcg | 0.125 mL (12-13 units) |
Combined daily injection (drawn into one syringe): 0.05 + 0.125 = 0.175 mL = 17 to 18 units.
Semaglutide (5 mg vial)
| Bac water | Concentration | 0.25 mg | 0.5 mg | 1 mg | 2.4 mg |
|---|---|---|---|---|---|
| 2 mL | 2.5 mg/mL | 0.10 mL (10 units) | 0.20 mL (20 units) | 0.40 mL (40 units) | 0.96 mL (96 units) |
| 2.5 mL | 2 mg/mL | 0.125 mL (12-13 units) | 0.25 mL (25 units) | 0.50 mL (50 units) | 1.20 mL (120 units, 2 syringes) |
Tirzepatide (10 mg vial)
| Bac water | Concentration | 2.5 mg | 5 mg | 7.5 mg | 10 mg |
|---|---|---|---|---|---|
| 2 mL | 5 mg/mL | 0.50 mL (50 units) | 1.0 mL (100 units) | 1.5 mL (150 units, 2 syringes) | 2.0 mL (200 units, 2 syringes) |
| 2.5 mL | 4 mg/mL | 0.625 mL (62-63 units) | 1.25 mL (125 units) | 1.875 mL | 2.50 mL |
GHK-Cu (50 mg vial, larger format)
| Bac water | Concentration | 1 mg dose | 2 mg dose | 5 mg dose |
|---|---|---|---|---|
| 5 mL | 10 mg/mL | 0.10 mL (10 units) | 0.20 mL (20 units) | 0.50 mL (50 units) |
| 10 mL | 5 mg/mL | 0.20 mL (20 units) | 0.40 mL (40 units) | 1.0 mL (100 units) |
How Much Bac Water to Add: The Decision
You can technically reconstitute most peptides with anywhere from 1 to 10 mL of bacteriostatic water. The choice affects how easy the math becomes:
- Round numbers: pick a bac water volume that gives whole-number concentrations (1 mg/mL, 2 mg/mL, 5 mg/mL) for easier dose math.
- Manageable injection volumes: aim for a daily injection in the 0.05 to 0.25 mL range. Too dilute and your injection volume gets uncomfortable; too concentrated and small dose adjustments become hard.
- Vial capacity: most 5 mg vials hold 3 to 5 mL maximum. 10 mg vials hold up to 10 mL. Do not exceed the vial capacity.
- Storage time: more dilute solutions degrade slightly faster. For peptides you use over weeks, more concentrated reconstitution is preferable.
The default we recommend for most peptides: 2 to 2.5 mL bac water per 5 mg vial. This gives 2 to 2.5 mg/mL concentrations and convenient injection volumes.
The Three Most Common Dosage Calculation Mistakes
Mistake 1: Confusing mg with mcg
1 mg = 1,000 mcg. Most peptides are dosed in micrograms (mcg). If your protocol says 250 mcg and you accidentally calculate 250 mg, you have just calculated 1,000x your target dose. Always double-check unit before dividing.
Mistake 2: Using the wrong syringe
Insulin syringes (units) and tuberculin syringes (mL) have different markings. 25 units on an insulin syringe = 0.25 mL. 25 marks on a tuberculin syringe = 1.25 mL (5x more). Using the wrong syringe with the wrong scale leads to either 5x underdose or 5x overdose. See our syringes guide.
Mistake 3: Inconsistent reconstitution between vials
Reconstituting the first vial with 2 mL and the next vial with 2.5 mL means your dose changes mid-protocol. Pick one reconstitution volume and use it for every vial of that peptide.
Quick Mental Math Shortcuts
Memorize these ratios for the most common reconstitution:
- 5 mg vial + 2.5 mL bac water = 2 mg/mL → 100 mcg = 5 units, 250 mcg = 12-13 units, 500 mcg = 25 units, 1 mg = 50 units
- 10 mg vial + 2 mL bac water = 5 mg/mL → 1 mg = 20 units, 2.5 mg = 50 units, 5 mg = 100 units
- 5 mg vial + 5 mL bac water = 1 mg/mL → 100 mcg = 10 units, 250 mcg = 25 units, 1 mg = 100 units
If you stick to one of these reconstitution schemes for each peptide, you only need to remember the unit-to-dose conversion once.
Frequently Asked Questions
Why do my doses look so small in the syringe?
Most peptide doses are 5 to 30 units (0.05 to 0.30 mL). This is normal; peptides are potent at low volumes. If your dose calculation results in 100+ units regularly, you may have over-diluted and should reconstitute more concentrated next time.
Can I trust online peptide dose calculators?
Yes for the math, but always verify the result against the formula yourself. Web calculators occasionally have unit conversion bugs (mcg vs mg). The math is simple enough that doing it manually with a calculator is foolproof.
What if my dose volume is awkward (e.g., 0.07 mL = 7 units)?
Round to the nearest unit (7 units in this case). Insulin syringes do not have sub-unit precision. The 0.7 unit difference is biologically negligible.
How do I split a dose between two injection sites?
Draw the full dose into one syringe, then inject half at one site and half at the other. The math is the same; only the delivery is split. This is mainly relevant for larger TB-500 doses (1.5+ mL) that are uncomfortable at a single site.
Can I use a 1 mL syringe instead of insulin?
Yes, but only if your dose is large enough to use the 1 mL scale precisely. For doses under 0.1 mL, the 1 mL syringe markings are too imprecise. Use insulin syringes for small doses; tuberculin or 1 mL for larger ones. See our syringes comparison.
Where can I get peptides with reconstitution support?
For research-grade peptides shipped with reconstitution guidance and dose calculation help via WhatsApp, see our pricelist. We walk first-time users through the calculation and verify your math before you start dosing.
This article is for informational and research-use purposes only. Always double-check your dose calculation before injection. When in doubt, message us for verification.