How the arithmetic works
Reconstitution means dissolving a freeze-dried powder in a liquid so it can be measured by volume. Three numbers describe the result. The first is the mass of peptide in the vial, printed on the label in milligrams. The second is the volume of liquid you add, in millilitres. Dividing the first by the second gives the concentration in mg per mL; multiplying that by 1,000 gives mcg per mL, which is the more useful figure because study regimens are usually reported in micrograms.
The third number is the amount you want in one draw. Divide it by the concentration and you have the volume of liquid that contains it. An insulin syringe converts that volume into units: a U-100 syringe is marked so that 100 units equal exactly 1 mL, so multiply millilitres by 100 to get units.
Reading a U-100 insulin syringe
Insulin syringes come in 0.3 mL (30 units), 0.5 mL (50 units) and 1 mL (100 units) sizes. The scale is printed in units, not millilitres, and the spacing of the marks differs by size: a 0.3 mL syringe usually has half-unit marks, a 1 mL syringe usually has two-unit marks. Read the volume at the edge of the plunger seal nearest the needle, with the syringe held at eye level. The diagram above shows where the draw falls on a 100-unit barrel.
The warnings the calculator shows are about readability, not about the amount. A draw under two units is a tiny volume where a small misread is a large fraction of the total; dissolving the vial in more water spreads the same amount over more marks. A draw over 100 units does not fit a standard insulin syringe at all.
Why the studies use bacteriostatic water
Published protocols typically reconstitute peptides with bacteriostatic water, which is sterile water containing 0.9% benzyl alcohol as a preservative. The preservative lets a multi-dose vial be entered more than once over several weeks. Plain sterile water has no preservative and is intended for single use. Neither changes the arithmetic, and the calculator treats the volume you enter the same way regardless of the diluent.
Common mistakes the calculator catches, and the ones it cannot
- mg versus mcg. The thousand-fold difference is the single most common error. The mcg/mg toggle exists so the amount is entered in the unit it was written in.
- Treating syringe units as peptide units. Syringe units are volume. The same 10-unit draw contains four times as much peptide from a 10 mg vial as from a 2.5 mg vial reconstituted in the same water.
- Forgetting the water volume. Two people with the same vial and the same amount in mind will draw different units if they added different amounts of water.
- Label accuracy. The calculator assumes the vial contains what the label says. It cannot see a certificate of analysis, a purity figure, or a mislabelled product.
- What to draw. The calculator never proposes an amount. That decision belongs to a licensed clinician who knows the person, the product, and its regulatory status.
Related
- Units converter for plain mg, mcg, mL and unit conversions without a vial.
- Study-dose calculators reproduce the arithmetic for regimens that cited studies reported, one compound at a time.
- Compound profiles list what each study administered, to whom, with the source.
Frequently asked questions
How do I calculate how many units to draw?
Divide the milligrams in the vial by the millilitres of water to get mg per mL. Multiply by 1,000 for mcg per mL. Divide the amount you want by that concentration to get millilitres, then multiply millilitres by 100 for units on a U-100 syringe. Example: 5 mg in 2 mL is 2,500 mcg/mL; 250 mcg is 0.1 mL, which is 10 units.
Does adding more water change the strength of the peptide?
No. The vial still contains the same total mass. More water lowers the concentration, so each unit on the syringe holds less peptide and a given amount takes more units. That is the only effect on the arithmetic.
Why does the result round to half a unit?
Most insulin syringes are marked in whole units, and some 0.3 mL and 0.5 mL syringes carry half-unit marks. The calculator shows the exact figure and the nearest half-unit mark so you can see how much rounding is involved.
What is the difference between mg and mcg?
One milligram (mg) is 1,000 micrograms (mcg, also written µg or ug). Vials are usually labelled in mg and study regimens are often reported in mcg, which is the most common source of a thousand-fold arithmetic error.
Are syringe units the same as the peptide amount?
No. Units on an insulin syringe measure volume: 100 units equal 1 mL. How much peptide is in that volume depends entirely on how the vial was reconstituted.
Does this calculator tell me what amount to use?
No. It converts an amount you enter into a syringe volume. Amounts reported in published studies are listed, with citations, on each compound page as research reporting, not as recommendations. Talk with a licensed clinician about anything you are considering.