Reconstitution Calculator

How this tool works · sources read September 30, 2026 · Grey Peptides Editorial Board

What the calculator computes

Every result on this page comes from one division and one multiplication. The milligrams in the vial divided by the millilitres of liquid added give the concentration. The dose divided by the concentration gives the volume to draw, and on a U-100 insulin syringe every 0.01 mL is one unit, so the volume times 100 is the number of units.

concentration (mg/mL) = vial (mg) ÷ liquid added (mL)
draw (mL) = dose (mg) ÷ concentration
units on a U-100 syringe = draw (mL) × 100
doses per vial = vial (mg) ÷ dose (mg), rounded down

Reverse mode runs the same formula backwards: pick the number of units you want each dose to be, and it returns the volume of liquid that produces that concentration. The water optimizer looks for a volume, in half-millilitre steps, that makes the dose land on a whole unit mark, because a whole mark is easier to read than 12.5 units. The multi-vial builder repeats the arithmetic for up to four vials, and the cost line divides the vial price by the doses it holds. None of these steps changes the dose. They only change how it is measured.

Micrograms and milligrams differ by a factor of 1,000, so 250 mcg is 0.25 mg; the unit button switches between them. Our guide to insulin syringe units works through the same arithmetic at six concentrations and explains U-100 against U-40 syringes.

Checked against a drug label

The simplest test of a dose calculator is to give it a drug label's own numbers and see whether it returns the label's answer. EGRIFTA SV, a tesamorelin product, comes as a 2 mg vial that the label says to mix with 0.5 mL of the supplied sterile water, and its dose is 1.4 mg, which the label says is 0.35 mL.¹ The calculator's arithmetic: 2 mg ÷ 0.5 mL is 4 mg/mL, and 1.4 mg ÷ 4 mg/mL is 0.35 mL, or 35 units. The tesamorelin preset loads exactly these numbers.

FORZINITY, the approved form of SS-31 (elamipretide), is a ready-made solution of 280 mg in 3.5 mL, or 80 mg/mL, and its dose for patients weighing at least 30 kg is 40 mg once daily.² Enter 280 mg and 3.5 mL and the calculator returns 0.5 mL, or 50 units, which is 40 mg at that concentration. When the math reproduces a label, the remaining uncertainty is not in the arithmetic but in what the arithmetic assumes.

What the math assumes

That the vial holds what its label says. The formula treats the number on the vial as milligrams of peptide. Synthetic peptides made by solid-phase synthesis, the standard method, come out as salts, usually trifluoroacetate, and how much counter-ion a peptide carries depends on its sequence, so the powder in a vial is not all peptide.³ Actual content can also simply differ from the label. When researchers bought semaglutide from illegal online pharmacies, the three vials that arrived contained 29% to 39% more semaglutide than labelled, and all three contained bacterial endotoxin.⁴ A dose calculated from a label that is off by a third is off by a third.

That the final volume equals the liquid added. For a few milligrams of powder this is close enough. A large amount of powder takes up volume of its own, so a 500 mg vial dissolved in 5 mL ends up somewhat more dilute than the arithmetic assumes.

That the syringe is U-100. Almost all insulin syringes sold for this purpose are, and every unit figure here assumes it. A U-40 syringe puts 40 marks in a millilitre instead of 100, which changes every number.

That the dose is yours to choose. The calculator measures a dose; it does not recommend one. Where a preset carries a dose, the preset says where the dose comes from.

Where the presets come from

A preset fills in a common vial size and a dose. The vial sizes are sizes that are commonly sold; nothing standardises them. The doses fall into three groups, and each preset names its group.

The half-life shown for each preset is the one in that compound's encyclopedia entry, read from our dataset when the page is built, and it says "undetermined" where no human measurement exists. Two presets were removed in September 2026: pentosan polysulfate, which is a polysaccharide rather than a peptide and has no entry here, and dihexa, whose preset dose was four times the contents of its own preset vial and for which no human dose has ever been studied.

The 28-day countdown

The tracker counts 28 days from the day a vial's stopper is first punctured. That number is not a measurement of how long a peptide stays intact. It is the standard beyond-use date for an opened multiple-dose vial: date it when first opened and discard it within 28 days unless the manufacturer specifies a different date.¹⁰ It is a sterility limit, tied to how long a preservative can be relied on once needles have entered the vial.

That is why the liquid matters. Bacteriostatic water for injection contains 0.9% benzyl alcohol as a preservative and is sold in multiple-dose vials; its label warns that it must not be used in newborns, because benzyl alcohol is toxic to them.¹¹ Sterile water without a preservative is for single use: EGRIFTA SV's label says to inject the dose immediately after mixing and throw away the rest.¹ The risk the rule guards against is real. When a hospital cultured 205 opened single- and multiple-dose vials, 11 (5.4%) were contaminated, most often insulin vials.¹² A vial that has been punctured many times at home, without the aseptic routine of a pharmacy, has at least as many chances to be contaminated.

Mistakes the calculator cannot catch

• Milligrams read as micrograms. A factor of 1,000. Check the unit button before reading the result.
• Units read as millilitres. A factor of 100: 5 units is 0.05 mL, not 5 mL.
• A unit number carried to a new vial. "Ten units" is only a dose at one concentration. If the next vial is mixed with a different volume, the same ten units deliver a different dose.
• The wrong syringe. Every unit figure here assumes a U-100 syringe.

These are not hypothetical. FDA has documented patients who drew 5 to 20 times their intended dose of compounded semaglutide from multiple-dose vials, some after confusing milligrams, millilitres and units, and clinicians who converted doses incorrectly.¹³ A poison control centre described people who injected ten times their intended dose, one of whom had received a vial and syringes with no instruction at all.¹⁴ The calculator does the arithmetic correctly every time; it cannot see which unit you meant, what is really in the vial, or which syringe is in your hand.

Sources

1. Theratechnologies Inc. EGRIFTA SV (tesamorelin) for injection, US prescribing information: 2 mg vial reconstituted with 0.5 mL Sterile Water for Injection; dose 1.4 mg (0.35 mL) once daily; use immediately and discard unused solution. DailyMed version of July 31, 2026, read September 30, 2026.
2. Stealth BioTherapeutics. FORZINITY (elamipretide) injection, US prescribing information: 280 mg/3.5 mL (80 mg/mL) single-patient-use vials; 40 mg subcutaneously once daily for patients weighing 30 kg or more. DailyMed version of December 12, 2025, read September 30, 2026.
3. Erckes, V. et al. (2025). Towards a Consensus for the Analysis and Exchange of TFA as a Counterion in Synthetic Peptides and Its Influence on Membrane Permeation. Pharmaceuticals (Basel), 18(8). PMID: 40872554 · doi:10.3390/ph18081163
4. Ashraf, A. R. et al. (2024). Multifactor Quality and Safety Analysis of Semaglutide Products Sold by Online Sellers Without a Prescription: Market Surveillance, Content Analysis, and Product Purchase Evaluation Study. Journal of Medical Internet Research, 26, e65440. PMID: 39509151 · doi:10.2196/65440
5. Novo Nordisk. OZEMPIC (semaglutide) injection, US prescribing information: initiate at 0.25 mg once weekly for 4 weeks. DailyMed version of June 10, 2026, read September 30, 2026.
6. Eli Lilly and Company. MOUNJARO (tirzepatide) injection, US prescribing information: starting dosage 2.5 mg once weekly for 4 weeks. DailyMed version of September 2, 2026, read September 30, 2026.
7. Cosette Pharmaceuticals. VYLEESI (bremelanotide) injection, US prescribing information: 1.75 mg subcutaneously as needed; no more than one dose within 24 hours; more than 8 doses per month not recommended. DailyMed version of November 18, 2025, read September 30, 2026.
8. Ancell, C. D. et al. (2001). Thymosin alpha-1. American Journal of Health-System Pharmacy, 58(10), 879-885. PMID: 11381492 · doi:10.1093/ajhp/58.10.886
9. Jastreboff, A. M. et al. (2023). Triple-Hormone-Receptor Agonist Retatrutide for Obesity - A Phase 2 Trial. New England Journal of Medicine, 389(6), 514-526. PMID: 37366315 · doi:10.1056/NEJMoa2301972
10. The Joint Commission. Multi-dose vials: managing multi-dose vials of injectable medication (standards FAQ): an opened or accessed multiple-dose vial is dated and discarded within 28 days unless the manufacturer specifies a different date. Read September 30, 2026. Joint Commission
11. Hospira, Inc. Bacteriostatic Water for Injection, USP, prescribing information: 0.9% (9 mg/mL) benzyl alcohol as a bacteriostatic preservative, multiple-dose container; not for use in neonates. DailyMed version of July 8, 2026, read September 30, 2026.
12. Baniasadi, S. et al. (2013). Microbial contamination of single- and multiple-dose vials after opening in a pulmonary teaching hospital. Brazilian Journal of Infectious Diseases, 17(1), 69-73. PMID: 23294643 · doi:10.1016/j.bjid.2012.09.005
13. US Food and Drug Administration (2024). FDA alerts health care providers, compounders and patients of dosing errors associated with compounded injectable semaglutide products. July 26, 2024. FDA
14. Lambson, J. E. et al. (2023). Administration errors of compounded semaglutide reported to a poison control center-Case series. Journal of the American Pharmacists Association, 63(5), 1643-1645. PMID: 37392810 · doi:10.1016/j.japh.2023.06.017

This explainer describes how the tool works and what its numbers rest on. It is not medical advice and does not recommend any dose or product.