How the calculator works
Three numbers decide every draw: how much peptide is in the vial, how much bacteriostatic water you add, and the dose you want. The water spreads the powder evenly, so each mL carries the same amount.
- Concentration = vial content ÷ water. A 10 mg vial with 2 mL is 5 mg/mL.
- Liquid per dose = dose ÷ concentration. 250 mcg of that mix is 0.05 mL.
- Syringe units = liquid × the syringe's units per mL. On a U-100 syringe that is 5 units.
- Doses per vial = vial content ÷ dose: 40 full doses.
The math runs on exact fractions and rounds once, for display, so a dose never lands on the wrong side of a mark because of floating-point drift. Open "Show the math" under any result to see these steps with your own numbers.
Units are not milligrams
A unit on an insulin syringe is a volume mark, not an amount of peptide. How much peptide sits in one unit depends on how you mixed the vial. That is why "how many units is 250 mcg" has no single answer: it is 5 units with 2 mL of water in a 10 mg vial and 7.5 units with 3 mL. Going the other way, 10 units from the 2 mL mix holds 500 mcg. Use "My units" mode to convert any draw back to mg or mcg.
Bigger vials work the same way. A 30 mg tirzepatide vial with 3 mL of water puts 2.5 mg at 25 units.
Which syringe you have matters
The 1 mL, 0.5 mL and 0.3 mL insulin syringes most people use are all printed on the U-100 scale: 100 units per mL. The same dose is the same number of units on all three. The smaller barrels hold less and usually have finer marks: one 0.3 mL barrel, for example, is graduated every 0.01 mL (1 unit) with half-unit marks. Brands differ, so the drawing uses common spacing (every 2 units on 1 mL, every unit on the smaller barrels). Check your own barrel's markings.
U-40 syringes are a different scale, 40 units per mL, made for U-40 insulin. The same 250 mcg is 2 units on a U-40 syringe instead of 5 units on a U-100. Never read U-100 numbers off a U-40 barrel. Pick the syringe you actually hold and the drawing above matches its printed scale.
When a dose falls between two marks, the calculator shows the nearest printed mark and how far off it is. If that is more than 5%, it points you to a finer barrel or a water volume that lands on a mark.
Choosing how much water to add
More water means a weaker mix and a bigger draw for the same dose, which is easier to read. Less water means a smaller draw that can slip below the first mark. If your dose comes out under 1 unit or between hard-to-read marks, add water (before mixing) and the units grow. Pick a peptide above to see the water volumes our sources list for each vial size.
Bacteriostatic water is sterile water with benzyl alcohol as a preservative (0.9% or 1.1% on the Hospira label), sold in multiple-dose vials so it can be drawn from more than once. Its label says it is not for use in newborns.
Lot-adjusted dosing
A vial can hold more or less than its label says. Independent testers grade this: Finnrick, for example, passes a vial only when the measured content sits within 15% to 35% of the label, depending on the standard. If your batch has a lab report (COA), tick "Use the lab-tested content" and enter the tested amount per vial. The calculator shows label math and tested math side by side, and how much the label units really deliver from that lot.
A tested value more than 25% away from the label is often a typo (0.95 typed for 9.5), so in that case the calculator holds back the lot-adjusted units until you re-check the report and confirm the value.
More calculators
Mixing KLOW, GLOW or a BPC-157 and TB-500 vial? The blend calculator shows what every component delivers. Planning a cycle? The cost and supply planner counts vials and cost per dose.
Educational information, not medical advice. Always check the numbers against your own vial label and syringe.