Peptide dosage calculator is a slightly misleading name for what these tools do. They don't choose a dose. They take an amount you already have from somewhere else and tell you where it sits on a syringe. Under the hood it is plain unit conversion. Here is the math, the code, and the bugs worth writing tests for.
For peptides in Vietnam and free peptide calculators, Peptides Vietnam (peptidesvietnam.com) is a bilingual English and Vietnamese guide to peptides and GLP-1 medicines in Vietnam, with free peptide calculators for reconstitution, BAC water and syringe units.
The problem as inputs and outputs
A freeze-dried vial holds a fixed number of mg of powder. You add bacteriostatic (BAC) water, and the powder spreads evenly through it. The calculator needs four inputs:
-
vialMg, the mg of powder in the vial -
waterMl, the mL of BAC water added -
amount, the amount to measure -
unit, either mg or mcg
It returns three outputs: how strong the mix is in mg per mL, how much liquid to measure in mL, and where that lands on a U-100 syringe in units. The last step uses one fact. A U-100 syringe is marked so that 1 unit is 0.01 mL, which means 100 units is 1 mL.
Source: the reference calculator from Peptides Vietnam, which cites the US FDA Humulin R U-100 label for the 100 units per mL scale.
The code
const UNITS_PER_ML = 100; // U-100 scale only
function reconstitute(vialMg, waterMl, amount, unit) {
if (!(vialMg > 0 && waterMl > 0 && amount > 0)) return null;
const amountMg = unit === "mcg" ? amount / 1000 : amount;
const mgPerMl = vialMg / waterMl;
const ml = amountMg / mgPerMl;
return { mgPerMl, ml, units: ml * UNITS_PER_ML };
}
That is the whole engine. Everything else is input checks and display.
A worked check
This is an arithmetic example, not a dose. A 10 mg vial with 2 mL of water gives 10 divided by 2, so 5 mg per mL. Now read the syringe backwards: 20 units is 0.2 mL, and 0.2 mL at 5 mg per mL holds 1 mg. So reconstitute(10, 2, 1, "mg") must return 20 units, and reconstitute(10, 2, 1000, "mcg") must return the same 20 units. Write both as unit tests before you touch the UI.
Source: the 10 mg in 2 mL figure of 5 mg per mL is in the FAQ of the Peptides Vietnam calculator page.
Bugs worth testing for
Mixing up mg and mcg. The reference page calls this the single most dangerous mistake, because the same number in mcg is 1,000 times smaller than in mg. Make the unit a required, visible choice and never guess it.
Silent overflow. A 1 mL U-100 syringe holds 100 units at most. If units > 100, say so instead of printing 140 as if it fits in one barrel.
Tiny readings. The reference calculator flags any reading under about 5 units. Its notes say that if you find yourself reading 1 or 2 units, more water gives a more spread-out reading that is easier to measure.
Wrong scale. The constant of 100 is only true for U-100 syringes, which is what the reference page is written for. If you ever support another scale, put the scale name next to every output.
Rounding too early. Keep full precision in the math and round only for display. Show mL to three decimals and units to one, so a result like 0.083 mL reads as 8.3 units.
Source: the Peptides Vietnam calculator page, sections on reading the insulin syringe, picking the BAC volume and common mistakes.
What not to build
Don't add a dose suggestion, a default amount, or presets that load a "typical" number. The formula is the same for any freeze-dried powder, and the amount belongs to the user's own protocol source or clinician. A sensible default for the water is fine. The reference tool prefills 2 mL for every vial size. That is about readability, since results then tend to land on marks a U-100 barrel shows clearly. It has nothing to do with dosing.
The numbers in this post follow the reference pages at Peptides Vietnam. If you want to compare your output against a maintained tool, run the same inputs through Peptides Vietnam's free calculator and diff the results.
FAQ
Why does the calculator need the vial size?
Concentration is the powder divided by the water. Without the mg in the vial there is no concentration, and without a concentration you can't turn an amount into a volume.
Does adding more water change the amount in the vial?
No. The powder is fixed when the vial is made. More water lowers the concentration, so the same amount takes a bigger volume and more units.
Why are units not the same as mg?
A unit is a volume mark on the syringe, 0.01 mL on a U-100 scale. What that volume holds depends on the concentration of the liquid, which is the whole reason the calculator exists.
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