This peptide calculator handles both steps of preparing a lyophilized (freeze-dried) peptide: reconstitution — how concentrated your solution becomes after adding bacteriostatic water — and dosing — how many units to draw on a standard U-100 insulin syringe. Enter the milligrams of peptide in the vial, the volume of BAC water you add, and your target dose, and it returns the syringe units, injection volume, concentration, and how many doses the vial holds.
Getting the mixing math right matters because peptides are dosed in micrograms while syringes are marked in units, so a small arithmetic slip changes the dose several-fold. This tool is provided for educational purposes only and does not replace guidance from a licensed pharmacist or healthcare provider.
How Peptide Reconstitution Works
Reconstitution means dissolving a dry peptide with bacteriostatic water to make an injectable liquid. Two simple relationships drive the whole peptide reconstitution calculation:
- Concentration (mg/mL) = peptide in vial (mg) ÷ BAC water added (mL)
- Dose volume (mL) = desired dose (mg) ÷ concentration (mg/mL)
Because a U-100 insulin syringe holds 100 units per milliliter, units to draw = dose volume (mL) × 100. Adding more water does not change how much peptide you inject — it only spreads the same peptide across a larger volume, making each unit easier to measure precisely. A lower concentration (more water) is often chosen when doses are tiny, so the mark on the syringe is not microscopic.
Measuring Your Dose on an Insulin Syringe
Insulin syringes are labeled in "units," not milliliters, which is where a peptide dosage calculator helps. On a U-100 syringe:
- 100 units = 1.0 mL (a full standard syringe)
- 50 units = 0.5 mL
- 10 units = 0.1 mL
So once you know the dose volume in mL, multiply by 100 to find the unit mark. Keep the concentration consistent across a vial so every dose lands on the same unit mark. Store the reconstituted vial refrigerated at roughly 2–8 °C, keep it away from light, avoid shaking (swirl gently to mix), and note that bacteriostatic water contains a preservative that extends usable life to around 28 days for many peptides — always follow the specific product and provider guidance.
Worked Example: 5 mg Vial + 2 mL BAC Water
Suppose you have a 5 mg peptide vial and add 2 mL of bacteriostatic water.
- Concentration = 5 mg ÷ 2 mL = 2.5 mg/mL (2,500 mcg/mL)
- For a 250 mcg dose: 250 mcg ÷ 2,500 mcg/mL = 0.1 mL
- Units to draw = 0.1 mL × 100 = 10 units on a U-100 insulin syringe
- Doses per vial = 5 mg ÷ 0.25 mg = 20 doses
So a 250 mcg dose is the 10-unit mark, and the vial provides 20 such doses. If you instead added 1 mL of water, the concentration would double to 5 mg/mL, the same 250 mcg dose would be only 5 units, and each mark would represent twice as much peptide.
How to Reconstitute Peptides, Step by Step
A peptide reconstitution calculator turns two numbers — the milligrams in your vial and the millilitres of liquid you add — into a concentration you can measure. Reconstitution itself means dissolving a freeze-dried (lyophilised) peptide powder in liquid so it can be drawn accurately. The arithmetic is simple; the accuracy comes from doing the steps in order.
1. Let the vial reach room temperature. Adding cold liquid to cold powder slows dissolution 2. Wipe both stoppers with an alcohol swab 3. Draw your chosen volume of bacteriostatic water into a syringe 4. Angle the needle so the water runs down the vial wall rather than jetting onto the powder. Peptides are fragile and a direct stream can damage them 5. Let it dissolve on its own, or swirl gently. Do not shake — agitation can denature the peptide 6. Wait until the solution is completely clear before drawing a dose
Once reconstituted, concentration is fixed by the two numbers you chose: the milligrams in the vial and the millilitres you added. Everything after that is division.
This page explains the measurement math only. It is not medical advice, it does not recommend any dose or compound, and nothing here should be used to make decisions about anything you put into your body — that is a conversation for a licensed clinician.
Concentration Chart: Common Vial and Water Combinations
Used as a peptide dosing calculator, the tool works from concentration, which is simply the vial amount divided by the water added:
Concentration (mg/mL) = Peptide in vial (mg) ÷ Water added (mL)
A 10 mg vial with 2 mL of water gives 5 mg/mL, which is 5,000 mcg/mL. The same 10 mg vial with 1 mL gives 10 mg/mL — double the strength, so every syringe marking carries twice as much.
Which to choose is a trade-off. More water gives a weaker solution and larger, easier-to-read volumes on the syringe. Less water concentrates it, which means smaller draws where a single tick mark of error matters more. Where a protocol or supplier specifies a volume, follow that.
| Vial | Water added | Concentration | Per insulin unit (0.01 mL) |
|---|---|---|---|
| 2 mg | 1 mL | 2 mg/mL (2,000 mcg/mL) | 20 mcg |
| 5 mg | 1 mL | 5 mg/mL (5,000 mcg/mL) | 50 mcg |
| 5 mg | 2 mL | 2.5 mg/mL (2,500 mcg/mL) | 25 mcg |
| 10 mg | 1 mL | 10 mg/mL (10,000 mcg/mL) | 100 mcg |
| 10 mg | 2 mL | 5 mg/mL (5,000 mcg/mL) | 50 mcg |
| 15 mg | 3 mL | 5 mg/mL (5,000 mcg/mL) | 50 mcg |
| 30 mg | 3 mL | 10 mg/mL (10,000 mcg/mL) | 100 mcg |
The last column is the most practical figure: how many micrograms sit in one tick mark of a U-100 insulin syringe at that concentration.
Reading an Insulin Syringe: Units, mL, and mcg
Peptides are usually drawn with a U-100 insulin syringe, which is marked in "units" rather than millilitres. The conversion is fixed:
- 100 units = 1 mL
- 1 unit = 0.01 mL
- 50 units = 0.5 mL
Those units measure volume, not the amount of peptide. How much peptide sits in a unit depends entirely on your concentration — which is exactly the confusion this calculator removes.
The full chain:
Volume (mL) = Dose ÷ Concentration, then Units = Volume × 100
Worked example. A 10 mg vial with 2 mL of water is 5,000 mcg/mL. For a 250 mcg dose: 250 ÷ 5,000 = 0.05 mL, and 0.05 × 100 = 5 units. The same 250 mcg from a 5 mg vial in 2 mL (2,500 mcg/mL) needs 0.1 mL, or 10 units — twice the draw for the identical dose.
Also keep the metric prefixes straight, since a factor-of-1,000 slip is the most consequential error in this whole calculation: 1 mg = 1,000 mcg, so 250 mcg is 0.25 mg.
Doses Per Vial and Bacteriostatic Water
How many doses a vial yields depends only on the vial amount and the dose — not on how much water you added, since water changes the concentration and the draw volume together:
Doses per vial = Vial amount ÷ Dose size
A 10 mg vial at 250 mcg per dose is 10,000 ÷ 250 = 40 doses. At 500 mcg it is 20 doses. The water volume is irrelevant to that count, which surprises people who expect adding more water to stretch a vial further.
On the liquid itself: bacteriostatic water is sterile water containing roughly 0.9% benzyl alcohol, which suppresses bacterial growth and is what allows a vial to be entered more than once. Plain sterile water and normal saline contain no preservative, so they are intended for single use.
Once reconstituted, a peptide is far less stable than the dry powder — refrigeration is standard, light and heat degrade it, and shelf life is measured in weeks rather than the months or years lyophilised powder can keep. Follow the storage guidance for your specific compound rather than a general rule, and discard anything cloudy or discoloured.
Frequently Asked Questions
How do I reconstitute peptides?
Bring the vial to room temperature, swab both stoppers, then draw your chosen volume of bacteriostatic water and let it run down the inside wall of the vial rather than jetting onto the powder. Swirl gently — never shake — and wait until the solution is completely clear. Concentration is then the vial milligrams divided by the millilitres you added.
What is bac water for peptides?
Bacteriostatic water is sterile water containing about 0.9% benzyl alcohol as a preservative, which suppresses bacterial growth and allows a vial to be entered more than once. Plain sterile water and saline have no preservative and are intended for single use.
How do I convert a peptide dose to insulin syringe units?
Divide the dose by the concentration to get millilitres, then multiply by 100. On a 5,000 mcg/mL solution, a 250 mcg dose is 250 ÷ 5,000 = 0.05 mL, which is 5 units. A U-100 syringe always holds 100 units per millilitre, so 1 unit is 0.01 mL of volume regardless of concentration.
How many mcg are in a mg?
1,000 micrograms make one milligram, so 250 mcg is 0.25 mg and 2.5 mg is 2,500 mcg. Mixing these up is a factor-of-1,000 error, which makes it the single most consequential mistake in reconstitution math.
Does adding more bacteriostatic water give me more doses?
No. Doses per vial is the vial amount divided by the dose size, and water is not in that equation. Adding more water lowers the concentration and raises the draw volume by the same factor, so the number of doses is unchanged — you are just measuring the same peptide in a larger liquid volume.
Is this peptide calculator medical advice?
No. It performs unit arithmetic — concentration, draw volume, and doses per vial — from numbers you provide. It does not recommend a dose, a compound, or a protocol, and it cannot account for your circumstances. Decisions about any injectable substance belong with a licensed healthcare professional.
How many units is 250 mcg on an insulin syringe?
It depends on concentration. With a 5 mg vial reconstituted in 2 mL of BAC water (2.5 mg/mL), a 250 mcg dose equals 0.1 mL, which is 10 units on a U-100 insulin syringe. Halving the water to 1 mL doubles the concentration, making the same 250 mcg dose just 5 units.
How much bacteriostatic water do I add to a peptide vial?
There is no single required amount — you choose the volume to set a convenient concentration. Common choices are 1, 2, or 3 mL per vial. More water spreads the peptide across more units, making small doses easier to measure precisely. The peptide amount injected stays the same regardless of how much water you add.
How do I calculate peptide concentration after mixing?
Divide the milligrams of peptide in the vial by the milliliters of bacteriostatic water you added. For example, a 10 mg vial mixed with 2 mL of water gives 5 mg/mL, or 5,000 mcg/mL. This concentration is what converts your target dose into a volume and then into syringe units.
How many doses are in a peptide vial?
Divide the total peptide (mg) by the dose (mg). A 5 mg vial dosed at 250 mcg (0.25 mg) yields 5 ÷ 0.25 = 20 doses. The amount of bacteriostatic water does not change the number of doses — only the total peptide and the dose size do.
How long does reconstituted peptide last?
Once mixed with bacteriostatic water and refrigerated at about 2–8 °C, many peptides remain usable for roughly 28 days because the preservative limits bacterial growth. Storage life varies by peptide, so keep it cold, protect it from light, and follow the specific product and provider instructions. This tool does not provide medical advice.