This is the question that decides whether a vial is worth what you paid for it — and it is the one most reconstitution charts skip. The answer is also the simplest calculation on this site: one division, no water involved, no syringe involved. But the simple answer comes with two honest caveats, and this page gives you both, because a number on paper is not the same thing as a number of draws you will actually get.
The formula
Doses (or amounts) in a vial = total peptide in the vial ÷ amount per injection. Both figures must be in the same unit — both in mcg, or both in mg.
- In micrograms: (vial mg × 1,000) ÷ dose mcg
- In milligrams: vial mg ÷ dose mg
The water volume does not change the count
This surprises people, so it is worth saying plainly: a 5 mg vial holds the same total peptide whether you add 1 mL, 2 mL or 3 mL of water. The water changes the concentration — and therefore how many units each dose measures — but the total amount of peptide in the vial was fixed when the vial was filled. A 5 mg vial at 250 mcg per amount holds 20 amounts at every water volume. What changes is the syringe reading: at 1 mL of water that amount is 5 units, at 2 mL it is 10 units, at 3 mL it is 15 units. Same count, different draw.
Worked examples
Worked example — 5 mg vial, example amount 250 mcg:
- Total in the vial: 5 × 1,000 = 5,000 mcg
- Amounts: 5,000 ÷ 250 = 20 amounts
Worked example — 10 mg vial, example amount 500 mcg:
- Total in the vial: 10 × 1,000 = 10,000 mcg
- Amounts: 10,000 ÷ 500 = 20 amounts
Worked example — 20 mg tirzepatide vial, example amount 2.5 mg:
- Work in milligrams: 20 ÷ 2.5 = 8 amounts
- Or in micrograms: 20,000 ÷ 2,500 = 8 amounts
The full table
Amounts per vial for common vial sizes and example amounts. Read across for your vial, down for your amount.
| Example amount | 2 mg vial | 3 mg vial | 5 mg vial | 10 mg vial | 20 mg vial | 30 mg vial | 50 mg vial |
|---|---|---|---|---|---|---|---|
| 100 mcg | 20 | 30 | 50 | 100 | 200 | 300 | 500 |
| 250 mcg | 8 | 12 | 20 | 40 | 80 | 120 | 200 |
| 500 mcg | 4 | 6 | 10 | 20 | 40 | 60 | 100 |
| 1 mg | 2 | 3 | 5 | 10 | 20 | 30 | 50 |
| 2 mg | 1 | 1.5 | 2.5 | 5 | 10 | 15 | 25 |
| 2.5 mg | 0.8 | 1.2 | 2 | 4 | 8 | 12 | 20 |
Check any cell yourself: 5 mg is 5,000 mcg, so at 500 mcg it is 5,000 ÷ 500 = 10. A 50 mg vial at 1 mg is 50,000 ÷ 1,000 = 50. The table is arithmetic, not a recommendation — the amounts are examples.
Caveat 1: fractional results
Some cells do not divide evenly. A 5 mg vial at an example amount of 2 mg gives 5,000 ÷ 2,000 = 2.5 amounts — two full amounts and a partial one that may not be drawable cleanly. A 2 mg vial at 2.5 mg gives 0.8 — less than one full amount, which means the vial does not hold that amount at all. Always round down when counting full amounts: 16.7 amounts means about 16 full amounts, not 17.
Caveat 2: the number on paper is a ceiling, not a promise
Liquid stays behind in the needle hub and in the shoulder of the vial, so the last amount on paper is frequently not recoverable. Sources that discuss this put it plainly: every figure here is a ceiling rather than a promise, because of dead space. If your calculation says 20 amounts, plan on 19 or 20 in practice — and do not stretch a vial past what you can draw cleanly. This is reported handling experience, not a measured figure, so no exact loss percentage is given here.
Worked examples across the site’s peptides
Same formula, different scales — which is why one table serves all nine calculator pages:
- BPC-157, 5 mg vial, 250 mcg: 5,000 ÷ 250 = 20 amounts
- TB-500, 5 mg vial, 2 mg: 5,000 ÷ 2,000 = 2.5 amounts
- CJC-1295, 2 mg vial, 100 mcg: 2,000 ÷ 100 = 20 amounts
- Ipamorelin, 5 mg vial, 300 mcg: 5,000 ÷ 300 = 16.7 amounts
- Semaglutide, 3 mg vial, 250 mcg: 3,000 ÷ 250 = 12 amounts
- Tirzepatide, 20 mg vial, 2.5 mg: 20,000 ÷ 2,500 = 8 amounts
- MOTS-C, 10 mg vial, 1 mg: 10,000 ÷ 1,000 = 10 amounts
- GHK-Cu, 50 mg vial, 1 mg: 50,000 ÷ 1,000 = 50 amounts
- Sermorelin, 5 mg vial, 250 mcg: 5,000 ÷ 250 = 20 amounts
A vial that outlasts its window
One more practical point, and it is not maths: a large vial can hold more amounts than fit inside the commonly cited storage window. A 50 mg GHK-Cu vial at 1 mg holds 50 amounts; a 30 mg tirzepatide vial at 2.5 mg holds 12. How long a mixed vial is said to keep is the least settled figure on this site — most sources cite around 28 days refrigerated with BAC water, and sources range from 7 days to 6 weeks. This page does not resolve that; it only notes that the count in the vial and the time the vial is said to keep are two different questions, and the smaller of the two decides how many amounts you actually get. Follow your product’s own label.
Frequently Asked Questions
Does adding more water give me more doses?
No. The water changes the concentration, not the total peptide. A 5 mg vial holds 20 amounts of 250 mcg whether you add 1 mL, 2 mL or 3 mL — only the units per amount change.
Why does my vial run out before the calculated count?
Most likely dead space: liquid left in the needle hub and the vial shoulder. The calculated count is a ceiling, not a promise. Small measuring errors across many draws add up the same way.
What does a fractional answer mean?
It means full amounts plus a partial one. 2.5 amounts is two full amounts and half of a third — round down when counting what you can actually draw.
Can I calculate this in milligrams instead of micrograms?
Yes, as long as both figures are in the same unit: vial mg ÷ amount mg. A 20 mg vial at 2.5 mg is 20 ÷ 2.5 = 8 amounts. Mixing units (mg vial ÷ mcg amount) without converting is a 1,000-fold error.
Does the calculator show this?
Yes — every calculator page on this site shows doses per vial next to the units, for whatever vial, water and amount you enter.
How long will one vial last me?
That depends on how often the amount is taken, which is a schedule question, not a maths question — and this site does not answer schedule questions. The count in the vial is the maths half; the rest belongs to your provider.
Try the calculator: Peptide Calculator
Related guides
- Reconstitution Guide
- How Much BAC Water Should You Add?
- Syringe Units Guide
- mg to mcg Conversion Guide
- BPC-157 vs TB-500: Reconstitution Maths Compared
Educational reference only — not medical advice. This guide describes maths and commonly reported handling steps only; it does not recommend any dose. Always confirm your dose and preparation with a licensed healthcare provider or pharmacist.