HCG · Reconstitution maths

Last updated: June 2026 · Reviewed June 2026 · Built by the InjectBuddy team

How do you reconstitute HCG? IU, BAC water and syringe units

To reconstitute HCG, divide the vial's IU strength by the milliliters of bacteriostatic water you add to get the concentration in IU per mL, then divide your prescribed dose in IU by that concentration to get the volume to draw. On a U-100 insulin syringe, multiply that volume in mL by 100 to read it as units. This guide explains every step, works through common vial-and-water combinations, and answers the questions people ask most.

Key takeaways

Concentration first: vial IU ÷ water mL = IU/mL. A 5,000 IU vial in 2 mL is 2,500 IU/mL.
Then the draw: dose IU ÷ IU/mL = mL; ×100 = units on a U-100 syringe.
Water volume is your choice (within the prescriber's instruction): more water spreads the dose over more units and is easier to read; less water gives a smaller draw.
Your dose never changes when you change water volume — only the unit mark changes.

Run your own numbers in the HCG dosage calculator — enter vial IU, water mL and your dose to get the exact syringe units.

What "reconstitution" means for HCG

HCG (human chorionic gonadotropin) ships as a freeze-dried (lyophilized) powder because the hormone is unstable in water for long-term storage. The manufacturer label for the 10,000 USP unit powder supplies it as a sterile lyophilized cake with bacteriostatic water as the diluent (DailyMed). Reconstitution simply means adding that water so the powder dissolves into an injectable solution.

The powder has a fixed total activity — say 5,000 IU or 10,000 IU — no matter how much water you add. Adding water only spreads the same total over a larger or smaller volume. That is the single idea behind every calculation here: the vial IU is fixed, and the water you pick decides the concentration, which decides your syringe units.

The diluent is usually bacteriostatic water — sterile water with about 0.9% benzyl alcohol added as a preservative so a multi-dose vial stays usable for repeated draws (DailyMed). Plain sterile water has no preservative and suits single-use mixing.

How this is calculated

There are only two steps, and both are division.

Step 1 — concentration. Divide the vial strength by the water you add:

concentration (IU/mL) = vial IU ÷ water mL

Step 2 — the draw. Divide your prescribed dose by that concentration, then convert to units:

volume (mL) = dose IU ÷ concentration (IU/mL)
units (U-100) = volume mL × 100

Because a U-100 syringe is marked so 100 units equals exactly 1 mL, the two steps collapse into a shortcut: units = dose IU × water mL × 100 ÷ vial IU. Use whichever form is clearer — they agree. The worked examples below show the long way and the result so you can check your own arithmetic.

HCG vial IU and water volume to IU per unit

This chart shows the concentration for common vial-and-water pairings, plus how many IU sit in each unit on a U-100 syringe. "IU per unit" is the handiest number: multiply it by the units you draw to see the dose, or divide your dose by it to see the units.

Vial	BAC water	Concentration	IU per unit	250 IU dose	500 IU dose
5,000 IU	1 mL	5,000 IU/mL	50 IU	5 units	10 units
5,000 IU	2 mL	2,500 IU/mL	25 IU	10 units	20 units
5,000 IU	3 mL	1,667 IU/mL	16.7 IU	15 units	30 units
5,000 IU	5 mL	1,000 IU/mL	10 IU	25 units	50 units
10,000 IU	2 mL	5,000 IU/mL	50 IU	5 units	10 units
10,000 IU	5 mL	2,000 IU/mL	20 IU	12.5 units	25 units
10,000 IU	10 mL	1,000 IU/mL	10 IU	25 units	50 units

Notice that 5,000 IU in 1 mL and 10,000 IU in 2 mL land on the same concentration (5,000 IU/mL) and the same units — the ratio of IU to water is what matters, not the vial size.

More bacteriostatic water spreads the same 500 IU dose across more syringe units — the dose is unchanged.

Worked examples

Each example reconstitutes a real vial size, finds the concentration, then converts a dose to a U-100 syringe mark. Check them against the chart above.

5,000 IU + 1 mL, 250 IU dose

Concentration = 5,000 ÷ 1 = 5,000 IU/mL. Volume = 250 ÷ 5,000 = 0.05 mL. 0.05 × 100 = 5 units. A small, hard-to-read draw — fine on a 0.3 mL syringe.

5,000 IU + 2 mL, 250 IU dose

Concentration = 5,000 ÷ 2 = 2,500 IU/mL. Volume = 250 ÷ 2,500 = 0.10 mL. 0.10 × 100 = 10 units. Doubling the water doubled the units for the same dose.

5,000 IU + 3 mL, 500 IU dose

Concentration = 5,000 ÷ 3 = 1,667 IU/mL. Volume = 500 ÷ 1,667 = 0.30 mL. 0.30 × 100 = 30 units. A 3 mL fill is a tidy middle ground for twice-weekly 500 IU dosing.

5,000 IU + 5 mL, 1,000 IU dose

Concentration = 5,000 ÷ 5 = 1,000 IU/mL. Volume = 1,000 ÷ 1,000 = 1.00 mL. 1.00 × 100 = 100 units. That fills a 1 mL syringe completely — a sign to use less water or a larger syringe.

10,000 IU + 2 mL, 500 IU dose

Concentration = 10,000 ÷ 2 = 5,000 IU/mL. Volume = 500 ÷ 5,000 = 0.10 mL. 0.10 × 100 = 10 units. High concentration means a tiny, precise draw — good for those comfortable reading small marks.

10,000 IU + 10 mL, 500 IU dose

Concentration = 10,000 ÷ 10 = 1,000 IU/mL. Volume = 500 ÷ 1,000 = 0.50 mL. 0.50 × 100 = 50 units. Same vial, five times the water, five times the units — easy reading at the cost of a fuller syringe.

Shortcut check: 5,000 IU + 2 mL, 350 IU dose

units = dose IU × water mL × 100 ÷ vial IU = 350 × 2 × 100 ÷ 5,000 = 70,000 ÷ 5,000 = 14 units. The one-line formula matches the two-step method.

Reverse: how much HCG is 8 units?

5,000 IU in 2 mL is 2,500 IU/mL, so each unit holds 2,500 ÷ 100 = 25 IU. 8 units × 25 IU = 200 IU. Multiply units by "IU per unit" to read any mark back as a dose.

Picking a water volume

Within whatever your prescriber specifies, the water volume is a readability decision, not a dose decision. Less water gives a tiny, precise draw that is easy to misread by a unit; more water spreads the dose over more units, which reads easily but fills more of the syringe. Many people pick a volume that puts their usual dose between 10 and 40 units, where a U-100 syringe is easiest to read.

Whatever you choose, keep clean technique: a fresh sterile needle and syringe each time, an alcohol wipe on the stopper, and the product's storage instructions. Reusing needles is a documented infection risk even when the maths is perfect (CDC; Manchikanti et al.). The reconstituted 10,000 USP unit label permits refrigerated use within 60 days (DailyMed) — defer to your own product's expiry rules.

Common mistakes

The biggest error is copying someone else's unit number without matching their water volume. Ten units only equals 250 IU if their vial-to-water ratio matches yours; on a different concentration, 10 units could be 100 IU or 500 IU. Always re-derive units from your vial and your water.

A second error is changing the water volume and assuming the dose changed too — it did not, only the unit mark moved. A third is ignoring the fluid left in the needle hub (dead space) when doses are tiny. When in doubt, re-enter the exact inputs in the calculator rather than reusing an old number.

So, how do you reconstitute HCG?

You reconstitute HCG by dissolving the freeze-dried powder in bacteriostatic water: divide the vial IU by the milliliters of water you add to get the concentration in IU/mL, then divide your prescribed dose by that concentration to find the draw volume in mL, and multiply by 100 to read the mark on a U-100 syringe. For a 5,000 IU vial mixed with 2 mL, that is 2,500 IU/mL — a 250 IU dose draws to 0.10 mL, or 10 units. Enter your exact vial and dose in the HCG dosage calculator to get the syringe units instantly.

FAQs

How do you reconstitute HCG?

Divide the vial IU by the milliliters of bacteriostatic water you add to get IU/mL, then divide your dose by that concentration for mL, and multiply mL by 100 for U-100 syringe units. A 5,000 IU vial in 2 mL is 2,500 IU/mL, so 250 IU draws to 10 units.

How much bacteriostatic water do I add to an HCG vial?

There is no single correct volume. The amount you add sets the concentration in IU/mL, which sets your syringe units. Common choices for a 5,000 IU vial are 1, 2, 3 or 5 mL, giving 5,000, 2,500, 1,667 or 1,000 IU/mL. Follow the volume your prescriber specifies.

How do I convert HCG IU to syringe units?

Divide vial IU by water mL to get IU/mL, divide your dose IU by that to get mL, then multiply mL by 100 for U-100 units. A 5,000 IU vial in 2 mL is 2,500 IU/mL, so 250 IU is 0.10 mL = 10 units.

Does the vial strength change my dose?

No. Your dose stays whatever was prescribed in IU. Vial strength and water volume only change the concentration, which changes how many units that fixed IU dose occupies.

How long does reconstituted HCG last?

The manufacturer label for the 10,000 USP unit powder states the reconstituted solution may be used within 60 days under refrigeration. Always follow your own product's instructions and discard if it looks cloudy or discolored.

Sources

DailyMed (U.S. National Library of Medicine). Chorionic Gonadotropin for Injection, 10,000 USP units — label (lyophilized powder, bacteriostatic water diluent, 60-day refrigerated use). DailyMed HCG label.
DailyMed (U.S. National Library of Medicine). Bacteriostatic Water for Injection, USP — label (0.9% benzyl alcohol as bacteriostatic preservative). DailyMed bacteriostatic water label.
Centers for Disease Control and Prevention. Safe Injection Practices to Prevent Transmission of Infections to Patients. CDC injection safety guidance.
Manchikanti L, Falco FJE, Benyamin RM, et al. Assessment of infection control practices for interventional techniques: a best evidence synthesis of safe injection practices and use of single-dose medication vials. Pain Physician. 2012;15(5):E573-E614. PubMed PMID: 22996856.

This guide is a maths and measurement reference, not medical advice. HCG dose, schedule, route, and diluent choice must come from your prescriber. Always follow your product's specific label and storage instructions.