How the calculator works
Every formula, assumption and rounding rule, in one place, so you can check any answer by hand.
The three steps
Every calculation on this site is the same three divisions, applied in order. The engine that runs them is one JavaScript file, and the tables on every page are generated from the same numbers at build time, so the tool and the pages cannot disagree.
| Step | Formula | Worked example: 10 mg vial, 2 mL water, 2 mg dose |
|---|---|---|
| Concentration | peptide in the vial ÷ water added | 10 mg ÷ 2 mL = 5 mg/mL |
| Draw volume | dose ÷ concentration | 2 mg ÷ 5 mg/mL = 0.4 mL |
| Syringe units | volume × units per mL of the syringe | 0.4 mL × 100 = 40 units on a U-100 syringe |
Reverse mode runs the same steps backwards: units ÷ units per mL gives the volume, and volume × concentration gives the dose.
Syringe scales
Units measure liquid, not drug. The four syringes offered are U-100 at 1 mL, 0.5 mL and 0.3 mL, all of which put 100 units in 1 mL, and U-40 at 1 mL, which puts 40 units in 1 mL. The same 0.4 mL is 40 units on a U-100 barrel and 16 units on a U-40 barrel. The default is U-100, 1 mL, because that is what nearly everything sold for human use is.
Units and conversions
1 mg is 1,000 mcg. Doses entered in mcg are divided by 1,000 before the maths runs. HGH is handled in international units (IU) throughout: the vial strength and the dose are both in IU, so the concentration is IU per mL and the ratio maths is identical. Blends (KLOW, GLOW, the BPC-157 and TB-500 blend, CJC-1295 with ipamorelin) are dosed as the total on the label; the split into each peptide is the label ratio applied to the draw, which is inferred, not measured.
Doses per vial, and how long a vial lasts
Doses per vial is the vial strength divided by the dose, rounded down to a whole number. Vial lasts is that whole number multiplied by the days between doses: 1 for daily, 0.5 for twice daily, 2 for every other day, 1.4 for five days on and two off, 2.33 for three times a week, 3.5 for twice weekly, 7 for weekly. Neither figure accounts for the small amount left in the vial or lost in the syringe.
Cost per dose
Optional. Vial price divided by doses per vial (using the exact, not rounded, number of doses), and vial price divided by the vial strength for the cost per mg or per IU.
Half-life curves
Where a human half-life is documented, the page draws the fraction remaining over four half-lives: remaining = 0.5 to the power of (time ÷ half-life). Where it is not documented, no curve is drawn and the page says so.
Rounding
Units are shown to one decimal place, volumes to three, concentrations to two, and doses to three decimal places in mg (four in the reverse-mode milligram figure) or one in mcg; blend splits are shown to the whole microgram. Rounding happens only at display time; every intermediate step uses the full value.
Warnings
The calculator warns, without changing the answer, when the draw is larger than the syringe holds, when it is under 2 units (hard to read accurately), when more than 5 mL of water is entered (most vials will not take it), when the concentration is over 50 mg/mL, and when a dose sits outside the range commonly reported for that compound. A dose larger than the whole vial is an error, not a warning.
Presets and review
Each compound carries a default vial size, water volume, dose, frequency and reported dose range. These are starting points for the maths, not recommendations. They were last reviewed on 3 September 2026. Always use the strength printed on your own vial.
Testing
The engine has an automated test suite of 143 checks covering the forward and reverse maths, every syringe scale, IU handling, every blend ratio, titration ladders, cost and decay. It runs before every deploy, and a deploy that fails it is not published.
Related calculators and charts
Tools
- Peptide calculator The general tool, any compound
- Reconstitution calculator How much water to add, and why it matters
- Bacteriostatic water calculator Pick a volume that lands where you can read it
- How to read an insulin syringe U-100 vs U-40, and the 2.5x error
- The Protocol Pack Free 25-page printable reference
- mg to units calculator Both directions, any concentration, with the reference tables
- 1 mg to units on an insulin syringe The conversion table for every common concentration
- Units to mg calculator The mark you drew, back into milligrams
- Methodology (this page)
- About Peptulator Who publishes it, independence and contact
- Embed the calculator Free widget for blogs, clinics and newsletters, credit link only
Every one of the 27 compound calculators, charts and tools: the full list.