Peptide Calculator
Convert vial strength, bacteriostatic water, and syringe units into concentration and injection volume. Reconstitution, reverse (units → dose), target-concentration, and vial-longevity math — all in one tool.
This is a unit-conversion aid, not medical guidance. It performs arithmetic on the numbers you enter — it does not recommend a dose for any compound. Dosing decisions must come from a licensed prescriber.
Concentration
2.5mg/mL
Concentration
2,500mcg/mL
Per Syringe Unit
25mcg
Injection Volume
0.100mL
Units to Draw
10.0u (U-100)
Doses per Vial
20
This calculator converts between vial strength, water volume, concentration, and syringe units — pure arithmetic, run entirely in your browser. It does not store or transmit anything you enter, and it does not suggest a dose for any compound. All reconstitution, dosing, and injection decisions should be made with a licensed prescriber.
How Peptide Reconstitution Math Works
Reconstitution turns a freeze-dried (lyophilized) vial into an injectable liquid by adding a diluent — usually bacteriostatic water. The math runs in three steps: concentration, then volume, then syringe units.
- 1Concentration: Divide the vial's total strength by the water volume added: Concentration (mg/mL) = Vial Strength (mg) ÷ Water Added (mL). Multiply by 1,000 for mcg/mL.
- 2Injection volume: Divide the desired dose by the concentration: Injection Volume (mL) = Dose (mg) ÷ Concentration (mg/mL). This is the physical liquid volume that dose occupies.
- 3Syringe units: Multiply the injection volume by the syringe barrel's units-per-mL scale: 100 for a U-100 or U-50 barrel, 40 for a U-40 barrel. This is the number you actually draw to on the syringe.
Worked Example
A vial contains 5 mg, and 2 mL of bacteriostatic water is added.
- Step 1: 5 mg ÷ 2 mL = 2.5 mg/mL (2,500 mcg/mL)
- Step 2: a 0.1 mg (100 mcg) dose ÷ 2.5 mg/mL = 0.04 mL
- Step 3: 0.04 mL × 100 (U-100 scale) = 4.0 units
Plug these same numbers into the Reconstitution tab above to see it computed live, including the syringe fill visual.
Reading an Insulin Syringe: U-100 vs. U-40 vs. U-50
"Units" on a syringe barrel are not a fixed volume — they depend entirely on which scale the barrel is printed with. The same physical draw reads as a different unit count on each type:
- 100U-100: 100 units = 1 mL, so 1 unit = 0.01 mL. The most common insulin syringe scale, typically sold in 0.3 mL (30u), 0.5 mL (50u), and 1.0 mL (100u) barrel sizes.
- 50U-50: the identical 100-units-per-mL scale as U-100, just printed on a smaller 0.5 mL barrel — 1 unit is still 0.01 mL, the barrel simply tops out at 50 units instead of 100.
- 40U-40: 40 units = 1 mL, so 1 unit = 0.025 mL — two and a half times larger than a U-100 unit. A draw of 0.25 mL reads as 25 units on a U-100 barrel but only 10 units on a U-40 barrel.
Because the same volume reads differently on each scale, using the wrong syringe type in a calculation is one of the most common arithmetic errors in reconstitution math — always confirm the printed scale on the barrel in hand before drawing to a calculated unit mark.
Worked Examples
These are arithmetic walkthroughs only — the numbers below are arbitrary inputs, not recommendations for any dose.
Example 1 — 5 mg vial, 2 mL water, 0.1 mg dose
- Concentration: 5 mg ÷ 2 mL = 2.5 mg/mL (2,500 mcg/mL)
- Per unit (U-100): 25 mcg
- Dose of 0.1 mg → 0.040 mL = 4.0 units
- Doses per vial: 50
Example 2 — 10 mg vial, 1 mL water, 2.5 mg dose
- Concentration: 10 mg ÷ 1 mL = 10 mg/mL (10,000 mcg/mL)
- Per unit (U-100): 100 mcg
- Dose of 2.5 mg → 0.250 mL = 25.0 units
- Doses per vial: 4
Example 3 — 2 mg vial, 3 mL water, 0.25 mg dose
- Concentration: 2 mg ÷ 3 mL = 0.6667 mg/mL (666.7 mcg/mL)
- Per unit (U-100): 6.7 mcg
- Dose of 0.25 mg → 0.375 mL = 37.5 units
- Doses per vial: 8
Conversion Reference Table
Pure arithmetic at common vial-and-water combinations — no dosing implication. Use the calculator above for any combination not listed here.
| Vial | Water | mg/mL | mcg/mL | mcg/unit (U-100) | mcg/unit (U-40) |
|---|---|---|---|---|---|
| 2 mg | 1 mL | 2 | 2,000 | 20 | 50 |
| 2 mg | 2 mL | 1 | 1,000 | 10 | 25 |
| 5 mg | 1 mL | 5 | 5,000 | 50 | 125 |
| 5 mg | 2 mL | 2.5 | 2,500 | 25 | 62.5 |
| 5 mg | 3 mL | 1.6667 | 1,666.7 | 16.7 | 41.7 |
| 10 mg | 1 mL | 10 | 10,000 | 100 | 250 |
| 10 mg | 2 mL | 5 | 5,000 | 50 | 125 |
| 10 mg | 3 mL | 3.3333 | 3,333.3 | 33.3 | 83.3 |
| 15 mg | 2 mL | 7.5 | 7,500 | 75 | 187.5 |
| 15 mg | 3 mL | 5 | 5,000 | 50 | 125 |
Common Mistakes & Edge Cases
- Mixing up mg and mcgMilligrams and micrograms differ by a factor of 1,000 — entering a dose as "250" without fixing the unit (250 mg vs. 250 mcg) changes every downstream number by three orders of magnitude. Always confirm which unit a vial label or a dose figure is actually printed in before entering it.
- Using a U-40 syringe with a U-100 calculation (or vice versa)A U-100 syringe reads 100 units per 1 mL; a U-40 syringe reads 40 units per 1 mL for the identical 1 mL of liquid. The same 0.25 mL draw is "25 units" on a U-100 barrel but "10 units" on a U-40 barrel. Drawing to the number of units calculated for one syringe type using a different syringe type delivers the wrong volume entirely.
- Forgetting that added water is the denominatorConcentration is vial strength divided by the water volume actually added, not the vial's labeled strength alone. Adding more bacteriostatic water than intended lowers the concentration and silently increases the injection volume (and units drawn) needed for the same dose.
- Treating "units" as if they were milligramsA syringe unit is a fixed fraction of a milliliter (0.01 mL on a U-100 scale, 0.025 mL on a U-40 scale) — it is not a mass unit and has no fixed mg or mcg value on its own. The mass delivered per unit depends entirely on the reconstituted concentration, so "20 units" means a different dose at every different concentration.
- Rounding the draw amount to a syringe's printed markingsMost insulin syringes are only marked in whole- or half-unit increments. A calculated draw of 13.7 units has to be read at the nearest printed mark, which introduces small rounding error — the smaller the calculated draw, the larger that error is as a percentage of the dose.