Water in, concentration out
Reconstitution has one job: turn a known amount of powder into a liquid whose strength you can state as a number. That number is the concentration, and it comes from a single division: concentration in micrograms per millilitre equals the vial amount in milligrams times 1,000, divided by the water in millilitres. Everything else on this page follows from it. If the vial holds 5 mg and you add 2 mL of water, the concentration is 5,000 ÷ 2 = 2,500 mcg/mL. Add only 1 mL and it is 5,000 mcg/mL. Add 5 mL and it is 1,000 mcg/mL. The powder did not change; only the dilution did. Every other number — the volume of a dose, the syringe units, the doses per vial — is downstream of this one division, which is why this page puts it first.
Worked examples: one vial, one dose, seven water amounts
The table below holds the vial and the dose fixed — 5 mg, 500 mcg as an arithmetic example — and varies only the water from 1 to 5 mL. Read it left to right and the trade-off is visible: as the water rises, the concentration falls, the volume per dose rises, and the units rise with it.
| Water (mL) | Concentration | Volume per dose | Units (U-100) |
|---|---|---|---|
| 1 mL | 5,000 mcg/mL | 0.10 mL | 10 units |
| 1.5 mL | 3,333.333 mcg/mL | 0.15 mL | 15 units |
| 2 mL | 2,500 mcg/mL | 0.20 mL | 20 units |
| 2.5 mL | 2,000 mcg/mL | 0.25 mL | 25 units |
| 3 mL | 1,666.667 mcg/mL | 0.30 mL | 30 units |
| 4 mL | 1,250 mcg/mL | 0.40 mL | 40 units |
| 5 mL | 1,000 mcg/mL | 0.50 mL | 50 units |
Arithmetic examples only, for a 5 mg vial and a 500 mcg dose. Change the numbers in the calculator above to see your own table.
Why dilution changes the units but not the dose
This is the point people trip over, so it is worth stating carefully. The dose is an amount of peptide — a number of micrograms. The water does not change that amount; it changes how much liquid carries it. At 1 mL of water the example dose takes 0.10 mL, which is 10 units. At 5 mL it takes 0.50 mL, which is 50 units. The dose is 500 mcg in both cases. What changed is the measurement: a larger volume is easier to read precisely on a syringe, because each unit marking represents a smaller share of the dose, while a smaller volume leaves less room for reading error in the other direction. That trade-off is a property of measurement, not of the peptide, and the calculator shows both sides of it in the same result tiles.
The auto-suggest button, explained
Next to the water field is a button that suggests a water amount for a round 20-unit draw. It is not making a choice for you; it is solving the formulas backwards. Units equal dose times water divided by vial times ten, so water equals units times vial times ten divided by dose. For the opening example — 5 mg, 500 mcg — that gives 20 × 5 × 10 ÷ 500 = 2 mL. The button only appears when the answer falls between 0.5 and 10 mL, and it tells you what it did in plain words when you press it. Round numbers are easier to read on a syringe and easier to double-check by hand; that is the whole reason the feature exists. If you prefer a different round number, the same formula works with any target: replace 20 with your number and the water follows.
Common mistakes in the mixing step
Three errors account for nearly every wrong result at this stage. The first is the mcg/mg mix-up: entering a dose in milligrams while the toggle says micrograms, or the reverse — a thousand-fold mistake that the results tiles expose immediately, because the concentration will look absurd next to the vial size. The second is forgetting that the water amount is the total liquid in the vial, not an addition on top of some other volume. The third is using a U-40 syringe with U-100 math: veterinary syringes measure differently, and a result computed for U-100 is meaningless on one. The calculator only does U-100 and says so on the syringe field. A quick hand-check catches all three: multiply vial mg by 1,000, divide by water mL, and confirm the concentration matches the tile before looking at anything else.
The boundary, restated
This page shows what water amounts do to concentration and units. It does not recommend any water amount, any dose, or any schedule. The examples, presets, and table are arithmetic illustrations. Questions about what to do belong to a licensed healthcare professional. Pure math only — not medical advice.