How to Calculate Peptide Dosages: Complete Guide
Peptide dosing trips up more people than reconstitution, injection technique, or storage combined. The math itself is simple — basic division and multiplication — but the units are confusing. Milligrams, micrograms, milliliters, units on a syringe.
Peptide dosing trips up more people than reconstitution, injection technique, or storage combined. The math itself is simple — basic division and multiplication — but the units are confusing. Milligrams, micrograms, milliliters, units on a syringe. These are four different measurement systems converging at the tip of a needle, and mixing them up means either underdosing (wasting peptide) or overdosing (unnecessary risk).
The confusion gets worse because peptides arrive as dry powder. You choose how much water to add, which sets the concentration, which determines how much liquid to draw for each dose. There is no fixed standard — two people with identical peptide vials can end up with completely different concentrations depending on their reconstitution choices. One is not wrong and the other right; they just need different volumes per dose.
This guide breaks down every calculation you need, from the basic concentration formula to body-weight-based dosing, complete with worked examples for common peptides. By the end, you will be able to convert between any unit, calculate any concentration, and draw the correct volume on any syringe.
Table of Contents
- The Units You Need to Know
- The Core Formulas
- Step 1: Calculate Your Concentration
- Step 2: Calculate Your Dose Volume
- Step 3: Convert to Syringe Units
- Worked Examples by Peptide
- Body-Weight-Based Dosing
- Concentration Reference Tables
- Understanding Insulin Syringes
- How Water Volume Affects Dosing
- Choosing the Right Water Volume
- Calculating Total Doses per Vial
- Common Calculation Mistakes
- Frequently Asked Questions
- The Bottom Line
- References
The Units You Need to Know
Before touching the math, you need to speak the language. Peptide dosing uses four measurement systems simultaneously. Here is what each one means and how they relate.
Weight Units
| Unit | Abbreviation | Relationship |
|---|---|---|
| Milligram | mg | 1 mg = 1,000 mcg |
| Microgram | mcg (or μg) | 1 mcg = 0.001 mg |
Peptide vial sizes are stated in milligrams (e.g., "5 mg BPC-157"). Individual doses are usually stated in micrograms (e.g., "250 mcg"). The conversion is straightforward: multiply milligrams by 1,000 to get micrograms.
- 5 mg = 5,000 mcg
- 2 mg = 2,000 mcg
- 10 mg = 10,000 mcg
Volume Units
| Unit | Abbreviation | Relationship |
|---|---|---|
| Milliliter | mL | 1 mL = 1 cc |
| Cubic centimeter | cc | 1 cc = 1 mL |
These are the same thing with different names. You will see both on syringes and vials. They are interchangeable.
Syringe Units (Insulin Syringes)
This is where the confusion lives. Insulin syringes are marked in "units" (abbreviated IU or U), not milliliters. On a standard U-100 insulin syringe:
100 units = 1 mL
This means:
- 10 units = 0.10 mL
- 25 units = 0.25 mL
- 50 units = 0.50 mL
- 5 units = 0.05 mL
These "units" have nothing to do with the potency of your peptide. They are purely a volume measurement on the syringe. A unit on a U-100 syringe is simply 0.01 mL — one hundredth of a milliliter.
Warning about U-40 syringes: Some insulin syringes are marked U-40 (40 units per mL). These are less common but still available. If you accidentally use a U-40 syringe and think in U-100 terms, your dose will be 2.5 times larger than intended. Always verify your syringe type before drawing.
The Core Formulas
You need three formulas. All three are simple division.
Formula 1: Concentration
Concentration (mg/mL) = Peptide Amount (mg) ÷ Water Volume (mL)
This tells you how much peptide is dissolved in each milliliter of your solution.
Formula 2: Dose Volume
Volume to Draw (mL) = Desired Dose (mg) ÷ Concentration (mg/mL)
This tells you how many milliliters of solution contain your desired dose.
Formula 3: Syringe Units
Units on Syringe = Volume to Draw (mL) × 100
This converts milliliters to units on a U-100 insulin syringe.
You can chain all three together into one master formula:
Units to Draw = [Desired Dose (mcg) ÷ (Peptide Amount (mcg) ÷ Water Volume (mL))] × 100
Or, simplified:
Units to Draw = (Desired Dose × Water Volume × 100) ÷ Peptide Amount
(where Desired Dose and Peptide Amount are in the same units — both mg or both mcg)
Step 1: Calculate Your Concentration
You have a vial of peptide (stated in mg) and you are going to add a chosen volume of bacteriostatic water (in mL). Dividing one by the other gives your concentration.
Example: 5 mg vial + 2 mL BAC water
Concentration = 5 mg ÷ 2 mL = 2.5 mg/mL
This means every milliliter of your solution contains 2.5 mg of peptide.
To express this in micrograms: 2.5 mg/mL = 2,500 mcg/mL.
Step 2: Calculate Your Dose Volume
Now that you know the concentration, you can calculate how much liquid contains your desired dose.
Example: You want a 250 mcg dose from a solution that is 2,500 mcg/mL.
Volume = 250 mcg ÷ 2,500 mcg/mL = 0.10 mL
You need to draw 0.10 mL from the vial.
Step 3: Convert to Syringe Units
On a U-100 insulin syringe, multiply milliliters by 100 to get units.
Example: 0.10 mL × 100 = 10 units
Draw to the 10-unit mark on your insulin syringe. That is 250 mcg of your peptide.
Worked Examples by Peptide
BPC-157 (5 mg vial)
Reconstitution: 5 mg vial + 2 mL BAC water = 2.5 mg/mL (2,500 mcg/mL)
| Desired Dose | Volume to Draw | Syringe Units (U-100) |
|---|---|---|
| 150 mcg | 0.06 mL | 6 units |
| 200 mcg | 0.08 mL | 8 units |
| 250 mcg | 0.10 mL | 10 units |
| 300 mcg | 0.12 mL | 12 units |
| 500 mcg | 0.20 mL | 20 units |
At 250 mcg/day, a 5 mg vial provides 20 doses (20 days of use).
Research dosing context: Animal studies on BPC-157 have primarily used 10 mcg/kg body weight. For a 75 kg person, that translates to approximately 750 mcg using a direct weight conversion, though human-equivalent dosing after allometric scaling from rats yields roughly 100–200 mcg. Clinical protocols typically range from 200–500 mcg per day.
Semaglutide (3 mg vial)
Reconstitution: 3 mg vial + 1.5 mL BAC water = 2 mg/mL (2,000 mcg/mL)
| Desired Dose | Volume to Draw | Syringe Units (U-100) |
|---|---|---|
| 250 mcg (0.25 mg) | 0.125 mL | 12.5 units |
| 500 mcg (0.5 mg) | 0.25 mL | 25 units |
| 1,000 mcg (1.0 mg) | 0.50 mL | 50 units |
| 1,700 mcg (1.7 mg) | 0.85 mL | 85 units |
| 2,400 mcg (2.4 mg) | 1.20 mL | 120 units (use 1 mL + 0.2 mL draws) |
Semaglutide is typically dosed once weekly with a gradual titration schedule: 0.25 mg for weeks 1–4, 0.5 mg for weeks 5–8, then increasing by 0.5 mg every 4 weeks to a maintenance dose of 1.7–2.4 mg weekly for weight management protocols.
At 0.25 mg weekly (starting dose), a 3 mg vial provides 12 weeks of use.
CJC-1295 (2 mg vial)
Reconstitution: 2 mg vial + 2 mL BAC water = 1 mg/mL (1,000 mcg/mL)
| Desired Dose | Volume to Draw | Syringe Units (U-100) |
|---|---|---|
| 100 mcg | 0.10 mL | 10 units |
| 150 mcg | 0.15 mL | 15 units |
| 200 mcg | 0.20 mL | 20 units |
CJC-1295 is often used at 100–200 mcg, 2–3 times per week. At 100 mcg three times weekly, a 2 mg vial lasts about 6–7 weeks.
Ipamorelin (5 mg vial)
Reconstitution: 5 mg vial + 2.5 mL BAC water = 2 mg/mL (2,000 mcg/mL)
| Desired Dose | Volume to Draw | Syringe Units (U-100) |
|---|---|---|
| 100 mcg | 0.05 mL | 5 units |
| 200 mcg | 0.10 mL | 10 units |
| 300 mcg | 0.15 mL | 15 units |
Ipamorelin is typically dosed at 200–300 mcg, 2–3 times daily. At 200 mcg three times daily, a 5 mg vial lasts approximately 8 days.
Body-Weight-Based Dosing
Some peptide protocols base the dose on body weight, expressed as micrograms per kilogram (mcg/kg). This is how most clinical research establishes dosing — it accounts for the fact that a 60 kg person and a 100 kg person have different distribution volumes.
The Body-Weight Formula
Dose (mcg) = Body Weight (kg) × Dose Rate (mcg/kg)
If your weight is in pounds, convert first: Weight (kg) = Weight (lbs) ÷ 2.205
Body-Weight Dosing Example: BPC-157 at 5 mcg/kg
| Body Weight (lbs) | Body Weight (kg) | Dose at 5 mcg/kg |
|---|---|---|
| 130 lbs | 59 kg | 295 mcg |
| 150 lbs | 68 kg | 340 mcg |
| 170 lbs | 77 kg | 385 mcg |
| 190 lbs | 86 kg | 430 mcg |
| 210 lbs | 95 kg | 475 mcg |
| 230 lbs | 104 kg | 520 mcg |
Allometric Scaling: From Animal Research to Human Doses
Most peptide dosing data comes from animal studies — primarily rats and mice. Converting an animal dose to a human-equivalent dose (HED) requires allometric scaling, which accounts for differences in body surface area and metabolism between species.
The FDA-accepted formula uses body surface area ratios:
Human Dose (mg/kg) = Animal Dose (mg/kg) × (Animal Km ÷ Human Km)
Where Km is a correction factor:
- Mouse Km = 3
- Rat Km = 6
- Human Km = 37
Practical example: A rat study uses BPC-157 at 10 mcg/kg. To convert to a human-equivalent dose:
Human Dose = 10 mcg/kg × (6 ÷ 37) = 1.62 mcg/kg
For an 80 kg person: 1.62 × 80 = ~130 mcg
This is why you often see clinical peptide doses that are dramatically lower than raw animal data might suggest. The scaling factor from rats to humans is roughly 1:6.2.
Important caveat: Allometric scaling provides estimates, not prescriptions. Only controlled human clinical trials can establish safe and effective doses.
Concentration Reference Tables
These tables show the resulting concentration and dose volumes for common vial sizes and water amounts. Use them as a quick reference when reconstituting your peptide.
5 mg Vial — Concentration by Water Volume
| BAC Water Added | Concentration (mg/mL) | Concentration (mcg/mL) |
|---|---|---|
| 0.5 mL | 10 mg/mL | 10,000 mcg/mL |
| 1.0 mL | 5 mg/mL | 5,000 mcg/mL |
| 1.5 mL | 3.33 mg/mL | 3,333 mcg/mL |
| 2.0 mL | 2.5 mg/mL | 2,500 mcg/mL |
| 2.5 mL | 2 mg/mL | 2,000 mcg/mL |
| 3.0 mL | 1.67 mg/mL | 1,667 mcg/mL |
10 mg Vial — Concentration by Water Volume
| BAC Water Added | Concentration (mg/mL) | Concentration (mcg/mL) |
|---|---|---|
| 1.0 mL | 10 mg/mL | 10,000 mcg/mL |
| 2.0 mL | 5 mg/mL | 5,000 mcg/mL |
| 2.5 mL | 4 mg/mL | 4,000 mcg/mL |
| 3.0 mL | 3.33 mg/mL | 3,333 mcg/mL |
| 5.0 mL | 2 mg/mL | 2,000 mcg/mL |
2 mg Vial — Concentration by Water Volume
| BAC Water Added | Concentration (mg/mL) | Concentration (mcg/mL) |
|---|---|---|
| 0.5 mL | 4 mg/mL | 4,000 mcg/mL |
| 1.0 mL | 2 mg/mL | 2,000 mcg/mL |
| 1.5 mL | 1.33 mg/mL | 1,333 mcg/mL |
| 2.0 mL | 1 mg/mL | 1,000 mcg/mL |
Quick Dose-Volume Lookup (U-100 Syringe)
For a 2.5 mg/mL solution (5 mg in 2 mL — one of the most common preparations):
| Dose | Volume | Syringe Units |
|---|---|---|
| 100 mcg | 0.04 mL | 4 units |
| 150 mcg | 0.06 mL | 6 units |
| 200 mcg | 0.08 mL | 8 units |
| 250 mcg | 0.10 mL | 10 units |
| 300 mcg | 0.12 mL | 12 units |
| 400 mcg | 0.16 mL | 16 units |
| 500 mcg | 0.20 mL | 20 units |
Understanding Insulin Syringes
Insulin syringes are the standard tool for peptide dosing. They are inexpensive, sterile, disposable, and marked in fine gradations that allow precise measurement of small volumes. But their unit markings can confuse anyone who is not already familiar with insulin injection.
U-100 Syringes (Standard)
The vast majority of insulin syringes sold today are U-100, meaning they are calibrated for insulin at 100 units per milliliter. For peptide users, the only thing that matters is the volume relationship: 100 units = 1 mL.
U-100 syringes come in three sizes:
| Syringe Size | Maximum Volume | Smallest Graduation | Best For |
|---|---|---|---|
| 0.3 mL (30 units) | 0.30 mL | 0.5 units (half-unit markings) | Very small doses; highest precision |
| 0.5 mL (50 units) | 0.50 mL | 1 unit | Most peptide doses |
| 1.0 mL (100 units) | 1.00 mL | 2 units | Larger doses or volumes |
Recommendation: For most peptide protocols, a 0.5 mL (50-unit) syringe offers the best balance of capacity and precision. If your dose is under 10 units, use a 0.3 mL syringe with half-unit markings for greater accuracy.
Reading the Syringe
Hold the syringe at eye level with the needle pointing up. The bottom of the plunger's rubber tip — not the top — marks your volume. This is called reading the "bottom of the meniscus" and is the standard method for all syringes.
Removing Air Bubbles
Air bubbles reduce the space available for your dose, meaning you draw less peptide than intended. After drawing your dose:
- Hold the syringe with the needle pointing up
- Tap the barrel firmly with your fingernail to dislodge bubbles
- Push the plunger up slowly until all air escapes and a small drop of liquid appears at the needle tip
- Verify the volume is still correct. If you pushed out too much, reinsert the needle into the vial and draw up to the correct mark
How Water Volume Affects Dosing
This is one of the most misunderstood aspects of peptide dosing. The amount of water you add does not change how much peptide is in the vial — it changes the concentration, which changes the volume you need to draw.
Same peptide. Same dose. Different water volumes. Different draw volumes.
| Scenario | Peptide | Water | Concentration | Dose (250 mcg) | Draw Volume |
|---|---|---|---|---|---|
| A | 5 mg | 1 mL | 5 mg/mL | 250 mcg | 0.05 mL (5 units) |
| B | 5 mg | 2 mL | 2.5 mg/mL | 250 mcg | 0.10 mL (10 units) |
| C | 5 mg | 5 mL | 1 mg/mL | 250 mcg | 0.25 mL (25 units) |
In all three scenarios, you receive exactly 250 mcg of peptide. The only difference is how much liquid you inject. More water = more dilute = larger injection volume for the same dose.
Choosing the Right Water Volume
Your goal is a concentration that makes your typical dose easy to measure on your chosen syringe.
Too Concentrated (Too Little Water)
If you add only 0.5 mL to a 5 mg vial, your concentration is 10 mg/mL. A 250 mcg dose would require 0.025 mL — just 2.5 units on a U-100 syringe. That is extremely difficult to measure accurately, especially on a standard 1 mL syringe where the smallest mark is 2 units.
Too Dilute (Too Much Water)
If you add 5 mL to a 5 mg vial, your concentration is 1 mg/mL. A 500 mcg dose would require 0.5 mL (50 units). That is a large injection volume for a subcutaneous shot — more liquid means more discomfort and more opportunity for the solution to pool under the skin.
The Sweet Spot
For most peptides and most dose ranges, adding 1–2 mL of BAC water to a standard vial hits the right balance. Your doses typically fall in the 5–30 unit range, which is easy to measure and produces a small, comfortable injection volume.
Quick guide:
| Typical Dose Range | Recommended Water Volume (5 mg vial) | Resulting Dose in Units |
|---|---|---|
| 100–200 mcg | 2–2.5 mL | 4–10 units |
| 200–500 mcg | 1.5–2 mL | 8–20 units |
| 500–1,000 mcg | 1–1.5 mL | 10–20 units |
Calculating Total Doses per Vial
Knowing how many doses you can extract from a single vial helps with planning and budgeting.
Total Doses = Peptide Amount (mcg) ÷ Dose Size (mcg)
Examples:
| Vial | Dose per Use | Total Doses | Duration (daily) | Duration (3x/week) |
|---|---|---|---|---|
| 5 mg BPC-157 | 250 mcg | 20 doses | 20 days | ~6.7 weeks |
| 5 mg BPC-157 | 500 mcg | 10 doses | 10 days | ~3.3 weeks |
| 3 mg semaglutide | 250 mcg weekly | 12 doses | — | 12 weeks |
| 3 mg semaglutide | 500 mcg weekly | 6 doses | — | 6 weeks |
| 2 mg CJC-1295 | 100 mcg | 20 doses | 20 days | ~6.7 weeks |
| 5 mg ipamorelin | 200 mcg | 25 doses | ~8 days (3x/day) | — |
Remember that reconstituted peptides should be used within 28 days (when mixed with bacteriostatic water and refrigerated). If your doses-per-vial math indicates the vial will last longer than 28 days, you have two choices:
- Use a smaller vial size
- Aliquot and freeze the surplus in single-use containers
Common Calculation Mistakes
Mistake 1: Confusing mg and mcg
A 500 mcg dose is 0.5 mg. A "500 mg dose" would be a thousand times larger — and potentially dangerous. Always double-check your units. Write them out in full (micrograms, milligrams) when doing calculations to avoid ambiguity.
Mistake 2: Using a U-40 Syringe and Thinking in U-100 Terms
If you accidentally use a U-40 syringe and draw to what you think is "10 units," you are actually drawing 0.25 mL (not 0.1 mL). That is 2.5 times your intended dose. Always check the syringe label: look for "U-100" printed on the barrel.
Mistake 3: Forgetting to Account for Water Volume
A 5 mg vial always contains 5 mg of peptide, but your concentration depends entirely on how much water you added. If you forget how much water went in, you cannot accurately dose. Write it on the vial label immediately after reconstitution.
Mistake 4: Not Accounting for Dead Space
Syringes have a small amount of "dead space" in the needle hub where liquid sits but does not get injected. For insulin syringes (especially low dead-space designs), this is minimal — usually less than 0.01 mL. For standard syringes with detachable needles, dead space can be 0.05–0.1 mL, which is significant for small doses. Insulin syringes with fixed needles minimize this problem.
Mistake 5: Rounding Too Aggressively
If your calculation says you need 7.5 units and you round to 10, you are overdosing by 33%. For small doses, precision matters. Use a syringe with fine-enough gradations for your dose — a 0.3 mL syringe with half-unit markings can measure 7.5 units exactly.
Frequently Asked Questions
Do I need to dose peptides based on body weight?
It depends on the peptide. Research protocols often use mcg/kg to normalize for body size. Prescribed peptides like semaglutide use fixed-dose titration schedules regardless of weight. If a protocol specifies mcg/kg, use the body-weight formula. If it specifies a flat dose (e.g., "250 mcg daily"), use that.
What if my dose falls between two marks on the syringe?
Get a more precise syringe. A 0.3 mL insulin syringe with half-unit markings lets you measure in 0.005 mL increments. If your dose still falls between marks, round to the nearest half-unit.
Can I use a tuberculin syringe instead of an insulin syringe?
Yes. Tuberculin syringes are marked directly in milliliters (mL) rather than units, which some people find more intuitive. They typically come in 1 mL size with 0.01 mL gradations. The only difference is the marking system.
What happens if I add the wrong amount of water?
The peptide still dissolves completely — you just end up with a different concentration than planned. Recalculate your concentration based on the actual water volume you added, then recalculate your dose volume accordingly. Everything still works; the numbers are just different.
How do I dose peptides that come in IU (International Units)?
Some peptides, particularly HGH and insulin, use International Units (IU). These are standardized biological activity units, not volume units. The conversion between IU and mg/mcg varies by peptide and manufacturer. Always check the product documentation for the specific conversion factor.
Should I use an online peptide calculator?
Online calculators are useful as a sanity check, but learn the formulas yourself first. Understanding the math means you can spot errors — including errors in the calculator. Several free tools exist at sites like OmniCalculator, PeptideCalculator.com, and others. Use them to verify your manual calculations, not as a replacement.
The Bottom Line
Peptide dosing math is three steps: calculate concentration, calculate dose volume, convert to syringe units. Every calculation flows from one formula: Concentration = Peptide Amount ÷ Water Volume. Once you know the concentration, everything else follows.
Write your concentration on the vial when you reconstitute. Use the right syringe for your dose range. Double-check your units — milligrams versus micrograms is a thousandfold difference. And when in doubt, recalculate. The 30 seconds it takes to verify your math is always worth it.
For the practical steps of reconstitution, see our reconstitution guide. For injection technique after drawing your dose, read the subcutaneous injection guide.
References
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Omni Calculator. "Peptide Dosage Calculator." Health Calculators. https://www.omnicalculator.com/health/peptide-dosage
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Reagan-Shaw, S., Nihal, M., & Ahmad, N. (2008). "Dose translation from animal to human studies revisited." FASEB Journal, 22(3), 659–661. https://pubmed.ncbi.nlm.nih.gov/17942826/
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U.S. Food and Drug Administration. "Guidance for Industry: Estimating the Maximum Safe Starting Dose in Initial Clinical Trials for Therapeutics in Adult Healthy Volunteers." FDA CDER, 2005.
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Bachem. "Handling and Storage Guidelines for Peptides." Bachem Knowledge Center. https://www.bachem.com/knowledge-center/peptide-guide/handling-and-storage-guidelines-for-peptides/
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Healthline. "Insulin Syringes Sizes and Lengths: Importance and How to Choose." https://www.healthline.com/health/diabetes/insulin-syringes-sizes
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Myco Medical. "Insulin Syringe Needle Sizes: A Complete Overview." https://www.mycomedical.com/post/insulin-syringe-needle-sizes
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United States Pharmacopeia. "Bacteriostatic Water for Injection, USP." USP Monograph. https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=ccadcf46-6a6f-436b-9bbc-17e2983a335f
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GenScript. "Peptide Storage and Handling Guidelines." GenScript Technical Resources. https://www.genscript.com/peptide_storage_and_handling.html