Lab tool
Peptide reconstitution calculator
Enter the mass in the vial and how much diluent you plan to add. The calculator gives you the resulting concentration and what each mark on a standard insulin syringe delivers.
The short answer
Peptide reconstitution is one division: concentration = peptide mass in the vial ÷ volume of diluent added. A 10 mg vial reconstituted with 2 mL of bacteriostatic water is 5 mg/mL, or 5,000 mcg/mL. Because one graduation on a U-100 insulin syringe is 0.01 mL, that solution carries 50 mcg in every unit mark and the 2 mL fill is 200 units in total.
The mass printed on the vial is the whole contents of the vial, never a per-millilitre figure — that single misreading is the most common reconstitution error. Everything below is arithmetic for laboratory measurement; the materials are supplied as laboratory research material, not as drugs, supplements or consumer products.
Bacteriostatic water for multi-draw vials; sterile water for single use.
Resulting concentration
5,000 mcg / mL
5 mg per mL
- Per syringe unit
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- Full syringe delivers
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- Vial contains
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Working backwards from a target
If you know the amount you want per syringe unit, this tells you how much diluent to add.
Add this much diluent
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How much to draw for a given amount
Using the concentration from the panel above, this converts an amount of peptide into a volume and into syringe unit marks.
Draw this much
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The formulas, written out
- Concentration
- concentration (mg/mL) = vial mass (mg) ÷ diluent volume (mL)
- Micrograms per millilitre
- mcg/mL = mg/mL × 1,000
- Mass in one U-100 syringe unit
- mcg per unit = mcg/mL × 0.01
- Volume to draw for a target mass
- volume (mL) = target mass (mcg) ÷ concentration (mcg/mL)
- Syringe units to draw
- units = volume (mL) ÷ 0.01
- Diluent volume for a target mass per unit
- volume (mL) = vial mass (mcg) × 0.01 ÷ target per unit (mcg)
The constant 0.01 is the volume of one graduation on a U-100 insulin syringe (1 mL ÷ 100 units). It is the same on a 0.3 mL, 0.5 mL or 1 mL barrel — only the number of graduations differs. See insulin syringe units (U-100) for why the scale is defined that way.
Worked example: a 10 mg vial in 2 mL
- Read the label. The vial is marked 10 mg. That is the total contents. In micrograms: 10 × 1,000 = 10,000 mcg.
- Choose the diluent volume. 2 mL of bacteriostatic water, directed down the inside wall of the vial.
- Divide for the concentration. 10 mg ÷ 2 mL = 5 mg/mL. Multiplied by 1,000 that is 5,000 mcg/mL.
- Convert to syringe units. 5,000 mcg/mL × 0.01 mL = 50 mcg in each unit mark. A 100-unit barrel filled to the top would hold 50 × 100 = 5,000 mcg, which is 5 mg — half the vial.
- Check how far the vial goes. 2 mL ÷ 0.01 mL = 200 units of solution in total.
- Solve the other direction. To put 250 mcg in one unit mark instead, the diluent volume is 10,000 mcg × 0.01 ÷ 250 = 0.4 mL, giving 25 mg/mL.
Reference table: common vial and diluent combinations
| Vial | Diluent | mg/mL | mcg/mL | mcg per unit | Units in vial |
|---|---|---|---|---|---|
| 5 mg | 1 mL | 5 | 5,000 | 50 | 100 |
| 5 mg | 2 mL | 2.5 | 2,500 | 25 | 200 |
| 10 mg | 1 mL | 10 | 10,000 | 100 | 100 |
| 10 mg | 2 mL | 5 | 5,000 | 50 | 200 |
| 10 mg | 3 mL | 3.333 | 3,333.33 | 33.33 | 300 |
| 15 mg | 2 mL | 7.5 | 7,500 | 75 | 200 |
| 15 mg | 3 mL | 5 | 5,000 | 50 | 300 |
| 20 mg | 2 mL | 10 | 10,000 | 100 | 200 |
| 20 mg | 4 mL | 5 | 5,000 | 50 | 400 |
| 30 mg | 3 mL | 10 | 10,000 | 100 | 300 |
“mcg per unit” is the mass in one 0.01 mL graduation of a U-100 syringe. “Units in vial” counts the graduations of solution the vial holds in total, which depends only on the diluent volume.
Common questions
How do you calculate peptide concentration after reconstitution?
Divide the peptide mass in the vial by the volume of diluent added. A 10 mg vial reconstituted with 2 mL of bacteriostatic water gives 10 ÷ 2 = 5 mg/mL, which is the same as 5,000 mcg per mL. The mass printed on the vial label is the whole contents of the vial, not a per-millilitre figure.
How many units is 1 mL on an insulin syringe?
On a U-100 insulin syringe, 1 mL is 100 units, so one unit mark is 0.01 mL. That ratio is fixed by the U-100 scale and does not change with barrel size: a 0.3 mL (30-unit) barrel and a 1 mL (100-unit) barrel both deliver 0.01 mL per graduation. To convert a concentration into mass per unit, multiply the mcg/mL figure by 0.01.
How much bacteriostatic water should be added to a 10 mg vial?
There is no single correct volume — the volume you choose sets the concentration. 1 mL of diluent in a 10 mg vial gives 10 mg/mL (100 mcg per syringe unit); 2 mL gives 5 mg/mL (50 mcg per unit); 3 mL gives 3.333 mg/mL (33.33 mcg per unit). Pick the volume that puts the amount you need to measure in the middle of the syringe scale, where reading error is smallest.
What diluent should be used to reconstitute a lyophilized peptide?
Bacteriostatic water is the usual choice for multi-draw vials because the benzyl alcohol suppresses microbial growth between draws. Sterile water suits single-use preparations. Peptides that resist aqueous solution may need a small volume of dilute acetic acid or another co-solvent first, added before the bulk of the diluent.
How should diluent be added to the vial?
Direct the stream down the inside wall of the vial rather than onto the powder cake, and let the material dissolve without agitation. Swirl gently if needed. Vigorous shaking introduces shear and foaming that can denature peptide in solution.
How long does reconstituted peptide remain usable?
Once in solution, store at 2–8 °C protected from light and work within the planned study window rather than holding solution indefinitely. Solution stability is markedly shorter than that of the sealed lyophilized powder, which is stable for extended periods at −20 °C.