Calculating a peptide dose requires exactly 2 numbers — the total peptide in the vial (in mcg) and the total bacteriostatic water you added (in units) — and one division: Total peptide (mcg) ÷ Total BAC water (units) = mcg per syringe unit, which tells you how much peptide each tick mark on your insulin syringe delivers.
The formula is simple, but the unit conversions trip people up. Milligrams vs micrograms is a 1,000× difference. Millilitres vs syringe units requires knowing that 100 units = 1 mL. Concentration, dose, and volume are three different numbers that are easily confused. Getting any of these wrong means every dose from that vial is wrong — underdosing wastes peptide and time, overdosing wastes peptide faster and may increase side effects. This guide covers the 3 core concepts, the 2-step formula with unit conversions, 4 complete worked examples for specific compounds, syringe selection, how to calculate a full protocol's supply, and the 7 most common dosing mistakes. Peptigrity's dosage calculator automates the maths, but understanding the formula lets you verify calculator output and catch input errors. For the companion guide on mixing the peptide with BAC water before dosing, see how to reconstitute peptides.
The 3 Numbers You Need to Know — Concentration, Dose, and Volume
Every peptide dose calculation involves 3 numbers — concentration (how much peptide per mL of solution), dose (how much peptide per injection), and volume (how much liquid to draw into the syringe) — and confusing any one of them with another is how dosing errors happen.
Concentration is the amount of peptide dissolved per unit of liquid, expressed as mcg/mL or mg/mL. It is determined entirely by the reconstitution step: Total peptide (mcg) ÷ Total BAC water (mL) = Concentration (mcg/mL). For example: 5,000 mcg ÷ 2 mL = 2,500 mcg/mL. This number is fixed the moment you reconstitute and does not change until the vial is empty.
Dose is the amount of active peptide you want per injection, measured in mcg (or mg for larger doses). This comes from your protocol — not from the vial label. The vial label tells you the total peptide; your protocol tells you how much to use per injection. Example: 250 mcg of BPC-157 per injection.
Volume is the amount of liquid you draw into the syringe to deliver that dose, measured in mL or units. It is calculated by dividing your desired dose by the concentration: 250 mcg ÷ 2,500 mcg/mL = 0.1 mL = 10 units. Volume is what your syringe shows; dose is what the peptide delivers. The same dose requires different volumes depending on how much BAC water you added during reconstitution.
The most important concept to internalise: adding more BAC water does not change the total peptide in the vial — it only changes the concentration. A 5 mg vial reconstituted with 1 mL and a 5 mg vial reconstituted with 5 mL both contain exactly 5,000 mcg of peptide. The first has a concentration of 5,000 mcg/mL (50 mcg per unit); the second has 1,000 mcg/mL (10 mcg per unit). Different concentration, different volume per dose, identical total peptide. The bacteriostatic water used for reconstitution — sterile water with 0.9% benzyl alcohol, prepared to USP pharmaceutical compounding standards — is the standard solvent; its volume is the only variable you control in the concentration equation. Peptigrity's dosage calculator computes all three numbers from your vial size, BAC water volume, and target dose. For how storage affects concentration over time, see the how to store peptides guide.
The 2-Step Dosing Formula — With Unit Conversions
The dosing formula has 2 steps — first calculate how many mcg each syringe unit delivers, then calculate how many units to draw for your dose — and the entire calculation takes less than 30 seconds once you know the conversion factors.
Prerequisite Conversions
Before calculating, convert everything to compatible units:
mg to mcg: Multiply by 1,000. A 5 mg vial = 5,000 mcg. A 10 mg vial = 10,000 mcg. A 2 mg vial = 2,000 mcg.
mL to units: Multiply by 100 (on a U-100 insulin syringe). 1 mL = 100 units. 2 mL = 200 units. 0.5 mL = 50 units.
Unit Conversion Reference:
From | To | Multiply by | Example |
|---|---|---|---|
mg | mcg | × 1,000 | 5 mg = 5,000 mcg |
mcg | mg | ÷ 1,000 | 250 mcg = 0.25 mg |
mL | Units (U-100) | × 100 | 2 mL = 200 units |
Units (U-100) | mL | ÷ 100 | 10 units = 0.1 mL |
Step 1 — Calculate mcg per Unit
mcg per unit = Total peptide in vial (mcg) ÷ Total BAC water added (units)
Example: 5,000 mcg ÷ 200 units (2 mL) = 25 mcg per unit. This means each tick mark on your insulin syringe delivers 25 mcg of peptide.
Step 2 — Calculate Units to Draw
Units to draw = Desired dose (mcg) ÷ mcg per unit
Example: 250 mcg ÷ 25 mcg/unit = 10 units. Draw to the 10-unit mark on your insulin syringe.
The One-Step Shortcut
The same maths combined into a single formula: Units to draw = (Desired dose ÷ Total peptide) × Total BAC water (in units). Example: (250 ÷ 5,000) × 200 = 10 units.
Doses per Vial
Total peptide (mcg) ÷ Dose per injection (mcg) = Number of doses. Example: 5,000 mcg ÷ 250 mcg = 20 doses per vial.
Pro tip: Choose your BAC water volume so that the resulting mcg-per-unit number produces round syringe markings for your target dose. If your dose is 250 mcg from a 5 mg vial, adding 2 mL (200 units) gives exactly 10 units per dose — clean and easy to read. Adding 1.5 mL would give 7.5 units per dose — harder to measure precisely on most syringes.
4 Worked Examples — Compound-Specific Dose Calculations
The dosing formula is the same for every peptide, but the practical application differs by compound — a 250 mcg BPC-157 dose draws only 10 units while a 2.5 mg TB-500 dose draws 50 units from the same size syringe, and a titrating semaglutide protocol changes draw volume every few weeks as the dose increases.
Example 1: BPC-157 — Standard Small-Dose Peptide
BPC-157, 5 mg vial, target dose 250 mcg per injection.
Reconstitute with 2 mL BAC water (200 units). Step 1: 5,000 mcg ÷ 200 units = 25 mcg/unit. Step 2: 250 mcg ÷ 25 = 10 units. Doses per vial: 5,000 ÷ 250 = 20 doses.
At 2 injections per day, this vial lasts 10 days — well within the 28-day reconstituted shelf life.
Example 2: CJC-1295 no DAC + Ipamorelin — Stacking Two Peptides
CJC-1295 without DAC, 2 mg vial, target dose 100 mcg. Ipamorelin, 5 mg vial, target dose 200 mcg. Both injected together 3× daily.
CJC-1295: Reconstitute with 1 mL (100 units). Step 1: 2,000 ÷ 100 = 20 mcg/unit. Step 2: 100 ÷ 20 = 5 units. Doses per vial: 2,000 ÷ 100 = 20 doses (~6.7 days at 3×/day).
Ipamorelin: Reconstitute with 2.5 mL (250 units). Step 1: 5,000 ÷ 250 = 20 mcg/unit. Step 2: 200 ÷ 20 = 10 units. Doses per vial: 5,000 ÷ 200 = 25 doses (~8.3 days at 3×/day).
To co-inject: draw 5 units from the CJC-1295 vial, then draw 10 units from the ipamorelin vial into the same syringe (total 15 units). Reconstitute each peptide in its own separate vial — never combine dry powders.
Example 3: Semaglutide — Titrating Dose Over Time
Semaglutide, 5 mg vial, titrating from 250 mcg to 1,000 mcg weekly.
Reconstitute with 2 mL (200 units). Concentration: 5,000 ÷ 200 = 25 mcg/unit.
Weeks 1–4 (250 mcg/week): 250 ÷ 25 = 10 units per injection, once weekly. Weeks 5–8 (500 mcg/week): 500 ÷ 25 = 20 units. Weeks 9+ (1,000 mcg/week): 1,000 ÷ 25 = 40 units.
Doses per vial change with dose: at 250 mcg = 20 weeks. At 500 mcg = 10 weeks. At 1,000 mcg = 5 weeks. A single 5 mg vial reconstituted at week 1 would expire at the 28-day mark — sufficient for the 250 mcg phase (4 doses used) with 16 doses remaining but expired. Plan to reconstitute a fresh vial at or before day 28.
Example 4: TB-500 — High-Dose Compound
TB-500, 5 mg vial, target dose 2.5 mg (2,500 mcg) per injection.
Reconstitute with 1 mL (100 units). Step 1: 5,000 ÷ 100 = 50 mcg/unit. Step 2: 2,500 ÷ 50 = 50 units = 0.5 mL. Doses per vial: 5,000 ÷ 2,500 = 2 doses only.
TB-500 is a high-dose compound — 2 doses per 5 mg vial is normal, not a sign you did the maths wrong. The 0.5 mL injection volume is larger than most peptide doses. If you prefer a smaller injection volume, reconstitute with 0.5 mL (50 units) instead: 5,000 ÷ 50 = 100 mcg/unit, and 2,500 ÷ 100 = 25 units — a more comfortable volume.
Quick-Reference Dosing Chart — 5 mg Vial
BAC Water Added | mcg per Unit | 100 mcg = | 250 mcg = | 500 mcg = | 1,000 mcg = |
|---|---|---|---|---|---|
1 mL (100 units) | 50 mcg | 2 units | 5 units | 10 units | 20 units |
2 mL (200 units) | 25 mcg | 4 units | 10 units | 20 units | 40 units |
2.5 mL (250 units) | 20 mcg | 5 units | 12.5 units | 25 units | 50 units |
Quick-Reference Dosing Chart — 10 mg Vial
BAC Water Added | mcg per Unit | 250 mcg = | 500 mcg = | 1,000 mcg = | 2,500 mcg = |
|---|---|---|---|---|---|
1 mL (100 units) | 100 mcg | 2.5 units | 5 units | 10 units | 25 units |
2 mL (200 units) | 50 mcg | 5 units | 10 units | 20 units | 50 units |
3 mL (300 units) | 33.3 mcg | 7.5 units | 15 units | 30 units | 75 units |
Which Insulin Syringe Should You Use?
The insulin syringe you choose directly affects dosing precision — a 10-unit dose is 4× easier to measure accurately on a 0.3 mL (30-unit) syringe than on a 1.0 mL (100-unit) syringe, because the graduation marks are physically more spread out, and the general rule is to always use the smallest syringe that can hold your total dose volume.
U-100 insulin syringes are available in 3 standard sizes:
0.3 mL (30-unit) syringe: Finest graduation marks — each tick typically represents 0.5 units (0.005 mL). Best for doses under 30 units. Ideal for small, precise doses such as BPC-157 (10 units), CJC-1295 (5 units), or ipamorelin (10 units). This is the most precise option for most peptide dosing.
0.5 mL (50-unit) syringe: Good middle ground — each tick typically represents 1 unit (0.01 mL). Suitable for most peptide doses between 10 and 50 units. The best general-purpose choice.
1.0 mL (100-unit) syringe: Coarsest graduation marks — each tick represents 2 units (0.02 mL). Best for large doses such as TB-500 (50 units) or semaglutide at higher titration levels (40+ units). Less precise for very small doses under 10 units — the markings are too close together to read reliably.
Rule of thumb: Use the smallest syringe that can hold your dose volume. A 10-unit dose is easy to read on a 0.3 mL syringe but nearly impossible to distinguish from 8 or 12 units on a 1.0 mL syringe. Needle gauge is typically 29–31 gauge, ½ inch length — standard for subcutaneous injection.
Critical disambiguation: syringe "units" are NOT International Units (IU). The "units" marked on an insulin syringe are simply volume markings — each unit equals 0.01 mL. International Units (IU) are a measure of biological potency used for HGH and insulin, where the mass-to-activity ratio varies by compound. For research peptides measured in mcg or mg, syringe "units" represent volume only. Confusing the two is a genuine source of dosing errors.
Syringe dead space — the tiny amount of liquid retained in the needle hub after fully depressing the plunger — is typically less than 0.5 units on standard insulin syringes, as noted in Sigma-Aldrich's peptide handling guidelines. This is negligible for most dosing purposes and does not require compensation in your calculation.
How to Calculate a Full Protocol's Supply
Knowing the per-injection dose is only half the planning equation — calculating the total milligrams needed for a complete protocol determines how many vials to purchase, and factoring in the 28-day reconstituted shelf life prevents wasting partially used vials that expire before you finish them.
The Planning Formula
Dose per injection (mcg) × Injections per day × Days per week × Number of weeks = Total mcg needed
Total mcg needed ÷ mcg per vial = Number of vials to purchase (always round up)
Worked Example 1: BPC-157 Healing Protocol
250 mcg × 2 injections/day × 7 days/week × 4 weeks = 14,000 mcg = 14 mg → 3 × 5 mg vials (round up from 2.8). At 2 doses/day from a 5 mg vial (20 doses), each vial lasts 10 days — comfortably within the 28-day shelf life.
Worked Example 2: CJC-1295 no DAC + Ipamorelin Stack
CJC-1295: 100 mcg × 3/day × 7 days × 12 weeks = 25,200 mcg ≈ 25.2 mg → 13 × 2 mg vials. Each vial provides ~6.7 days at 3×/day (20 doses), so you reconstitute a new vial approximately every week.
Ipamorelin: 200 mcg × 3/day × 7 days × 12 weeks = 50,400 mcg ≈ 50.4 mg → 11 × 5 mg vials. Each vial provides ~8.3 days at 3×/day (25 doses).
Worked Example 3: Semaglutide Titration
4 weeks at 250 mcg/week + 4 weeks at 500 mcg/week + 4 weeks at 1,000 mcg/week = 1,000 + 2,000 + 4,000 = 7,000 mcg = 7 mg → 2 × 5 mg vials (round up from 1.4).
Two Planning Factors Most People Miss
The 28-day shelf life constraint: If your dosing schedule produces 30 doses per vial but you only inject once daily, you will use only 28 doses before the vial's reconstituted shelf life expires — wasting 2 doses. For once-weekly protocols (like semaglutide), a 5 mg vial reconstituted at 250 mcg/week provides 20 weekly doses but expires after 4 weeks, meaning you use only 4 doses (1,000 mcg) and discard 4,000 mcg. In this scenario, purchasing smaller vials (2 mg) may reduce waste.
Dead space and vial retention loss: Assume approximately 5% loss over the life of a vial due to residual liquid you cannot extract — the last fraction of a millilitre that the needle cannot reach at the bottom of the vial. Budget one extra vial per 15–20 vials purchased to account for cumulative loss.
For sourcing, Peptigrity's reviewed peptide shops directory provides vendor-independent quality data to support the purchase decisions this planning informs.
7 Dosing Mistakes That Lead to Wrong Doses
The 7 most common peptide dosing mistakes — confusing mg with mcg, confusing units with mL, confusing IU with syringe units, using the wrong syringe, forgetting to recalculate after parameter changes, not tracking vial depletion, and rounding errors on fractional units — are all preventable with the formula and tools described above, and the single most dangerous is the mg/mcg confusion, which produces a 1,000-fold dosing error.
Mistake 1: Confusing mg with mcg. The single most dangerous dosing error. 250 mcg = 0.25 mg. If you calculate the syringe volume for "250 mg" instead of "250 mcg," you are attempting a dose 1,000 times too large — which would exceed the entire contents of most vials. Fix: Always convert the vial label from mg to mcg first, before any other calculation. Write both units down.
Mistake 2: Confusing units with mL. "10 units" on an insulin syringe = 0.1 mL, not 10 mL. A calculator output of "0.1 mL" is the same as "10 units" — they are the same volume expressed differently. Fix: Memorise the single conversion: 100 units = 1 mL for U-100 syringes.
Mistake 3: Confusing IU (International Units) with syringe "units." IU is a measure of biological potency used for HGH, insulin, and a few other compounds. Syringe "units" are volume markings (1 unit = 0.01 mL). They are not interchangeable. A protocol calling for "2 IU of HGH" requires a separate conversion based on the specific HGH product's IU-to-mg ratio. Fix: For research peptides measured in mcg, ignore IU entirely — use only mcg, mL, and syringe units.
Mistake 4: Using the wrong syringe size. Drawing a 5-unit dose on a 1.0 mL (100-unit) syringe is like trying to measure a teaspoon with a bucket — the graduation marks are too close together to read reliably. Fix: Match syringe size to dose volume. Under 30 units → 0.3 mL syringe. 30–50 units → 0.5 mL syringe. Over 50 units → 1.0 mL syringe.
Mistake 5: Forgetting to recalculate when changing vial size or BAC water volume. Switching from a 5 mg to a 10 mg vial — or changing from 2 mL to 1 mL of BAC water — changes the mcg-per-unit ratio. Drawing the same number of units delivers a different dose. Fix: Recalculate from scratch for every new vial reconstitution. Never assume the units-to-dose ratio carries over.
Mistake 6: Not tracking vial depletion. As you draw doses, remaining volume decreases. The concentration stays the same, but you may draw air if you try to extract more than what remains — resulting in an underdose. Fix: Label each vial with the reconstitution date, concentration (mcg/unit), total doses, and a tick-off counter for each draw. Discard at the 28-day mark regardless of remaining volume.
Mistake 7: Rounding errors on fractional units. If the calculation yields 7.3 units, a standard 1.0 mL syringe with 2-unit tick marks cannot measure this precisely. Fix: Either round to the nearest whole or half unit (7 or 7.5 units — a minor ~3–4% variance, clinically insignificant for most research peptides), or adjust your BAC water volume during reconstitution to produce round numbers.
Peptigrity's dosage calculator eliminates arithmetic errors by computing the result automatically, and the platform's independent lab tests verify that the compound in the vial matches the label — because even perfect dose calculations are meaningless if the peptide itself is mislabelled or degraded. The peptide impurities literature documents how synthesis byproducts and degradation products can alter the effective dose even when the vial label and your maths are correct, which is why analytical verification complements accurate dosing.
Frequently Asked Questions
Does adding more bacteriostatic water change how much peptide is in the vial?
No. The total peptide is fixed by the manufacturer and does not change regardless of how much BAC water you add. A 5 mg vial contains 5,000 mcg whether you add 1 mL or 5 mL of water. What changes is the concentration (mcg/mL) and therefore the volume you need to draw per dose. More water = lower concentration = more units per dose. Less water = higher concentration = fewer units per dose. The total peptide delivered across all doses remains the same.
How do I adjust my dose when switching from a 5 mg vial to a 10 mg vial?
Recalculate from scratch. A 10 mg vial contains twice the peptide. If you add the same 2 mL of BAC water, the concentration doubles: from 25 mcg/unit (5 mg vial) to 50 mcg/unit (10 mg vial). What was 10 units for 250 mcg from the 5 mg vial becomes 5 units for the same 250 mcg from the 10 mg vial. The dose (250 mcg) stays identical — only the draw volume changes. Always recalculate mcg per unit whenever any input changes.
Can I pre-fill syringes for the week?
This is done by some practitioners for convenience, but it introduces risks. Pre-filled syringes expose the peptide to the syringe barrel (polypropylene) and needle hub for an extended period, potentially affecting stability. Insulin syringes are designed for single use and are not validated for multi-day storage. If you pre-fill, store syringes capped, needle-up, refrigerated at 2–8°C, and use within 48–72 hours maximum. Label each with the compound name, dose in mcg, and fill date.
What if my calculation gives a fraction like 7.3 units?
Fractional units are a syringe-reading problem, not a math problem. You have 2 options: round to the nearest whole or half unit (7 or 7.5 units), accepting a minor dose variance of ~3–4% that is clinically insignificant for most research peptides; or adjust your BAC water volume during reconstitution to produce a round number. For example, adding 2.5 mL instead of 2 mL to a 5 mg vial changes mcg per unit from 25 to 20, and a 200 mcg dose becomes exactly 10 units instead of 8.
Is the dosing formula different for semaglutide or tirzepatide?
The formula is identical for every peptide — total mcg ÷ total units = mcg per unit. What differs for semaglutide and tirzepatide is the dose range (typically 250–2,500 mcg per week vs the 100–500 mcg per injection used for most research peptides) and the frequency (once weekly vs 1–3× daily). The calculation mechanics are the same. The one nuance: pharmaceutical semaglutide (Ozempic) comes in pre-filled injection pens with pre-set doses — the dosing formula and Peptigrity's calculator are relevant only for compounded or research vials that require manual reconstitution and dosing. For the regulatory context on compounded vs pharmaceutical peptide products, the FDA's compounding guidance outlines the distinction.
This article is for educational and informational purposes only and does not constitute medical advice. Peptides discussed may be investigational compounds not approved by the FDA for human use. Always consult a qualified healthcare provider before using any peptide or research compound. Peptigrity is an independent review platform and does not sell, endorse, or recommend specific products or vendors.
