Last updated: June 2026 · Reviewed June 2026 · Built by the InjectBuddy team
Peptide Terms Glossary: 20 Words That Drive Dose Math
A peptide terms glossary defines the handful of words that decide how much liquid you actually draw: lyophilized, reconstitution, bacteriostatic water, concentration, mg, mcg and units. Get those seven straight and almost every peptide dosing question becomes simple arithmetic. This page defines each term in plain English, then proves the maths with worked examples so the numbers are never a mystery.
Key takeaways
- mg and mcg are mass (how much peptide); mL is volume (how much liquid); units are syringe marks (100 units = 1 mL on a U-100 barrel). These are three different things.
- Concentration ties them together: concentration (mcg/mL) = total peptide ÷ water added. Dose volume = dose ÷ concentration.
- 1 mg = 1,000 mcg. Most peptides are dosed in mcg, so a 5 mg vial holds 5,000 mcg.
- Run your own numbers in the peptide reconstitution calculator before you draw.
The glossary 20 peptide terms, defined plainly
Below is the working vocabulary of a peptide vial. Each term is defined in one sentence, with a concrete example so you can see it in numbers. A peptide itself is just a short chain of amino acids — a small fragment of a protein — usually supplied as a dry powder you mix yourself.
| Term | Plain definition | Example |
|---|---|---|
| Lyophilized | Freeze-dried into a dry powder or pellet so it stays stable in storage | A 5 mg pellet at the bottom of the vial |
| Reconstitution | Adding liquid to turn the dry powder back into an injectable solution | 5 mg powder + 2 mL water = solution |
| Bacteriostatic water (BAC) | Sterile water with 0.9% benzyl alcohol that slows bacterial growth in a punctured vial | Draw 2 mL of BAC water to mix the vial |
| Diluent | The general word for whatever liquid you add (here, BAC water) | 2 mL is the diluent volume |
| Concentration | How much peptide sits in each mL after mixing | 5 mg ÷ 2 mL = 2.5 mg/mL |
| mg (milligram) | A mass; the total peptide is usually printed in mg | Vial is labelled 5 mg |
| mcg (microgram) | A smaller mass; 1 mg = 1,000 mcg. Most peptide doses use mcg | 250 mcg = 0.25 mg |
| IU (international unit) | A potency-based dose unit used for some compounds (e.g. HCG), not interchangeable with mcg | 500 IU on an HCG vial |
| mL (milliliter) | A volume; how much liquid you draw into the syringe | Draw 0.10 mL |
| Unit (U-100) | A syringe mark where 100 units = 1 mL | 0.10 mL = 10 units |
| Dose | The amount of peptide you intend to inject (a mass) | Target dose 250 mcg |
| Volume | The amount of liquid that carries that dose | 0.10 mL carries 250 mcg here |
| Dead space | Liquid left in the needle hub after injecting, slightly wasted each time | ~0.05 mL in a typical hub |
| Beyond-use date (BUD) | The date after which a reconstituted vial should be discarded | Many fridge-stored vials: ~28 days |
Notice the three families: mass (mg, mcg, IU), volume (mL) and syringe marks (units). The whole job of peptide concentration is converting between them.
How this is calculated the only two equations you need
Every term above plugs into two lines of arithmetic. First, find concentration from how much peptide and water are in the vial. Second, divide your dose by that concentration to get the volume to draw, then multiply by 100 for the unit mark.
- Concentration = total peptide ÷ water added. Keep the mass unit consistent (work in mcg to match how doses are written).
- Volume (mL) = dose ÷ concentration.
- Units (U-100) = volume in mL × 100.
That is the entire engine. The peptide reconstitution calculator does these three steps for you, but doing them by hand once makes the glossary stick. Because peptides are measured in mcg, converting a vial's mg to mcg first (multiply by 1,000) avoids the most common decimal slip.
Worked examples the terms in action
Each block takes the glossary words and runs the arithmetic. Numbers are illustrative, not dose advice.
A vial holds 5 mg of peptide and you add 2 mL of BAC water. Concentration = 5 mg ÷ 2 mL = 2.5 mg/mL = 2,500 mcg/mL. That single number drives every draw from this vial.
Same 2,500 mcg/mL vial, dose 250 mcg. Volume = 250 ÷ 2,500 = 0.10 mL. On a U-100 syringe that is 0.10 × 100 = 10 units.
Take the same 5 mg vial but add 1 mL instead. Concentration = 5,000 mcg/mL, so a 250 mcg dose = 250 ÷ 5,000 = 0.05 mL = 5 units. Same dose, half the water, half the units. The mark moved because the concentration did.
A protocol says 0.5 mg. Convert: 0.5 × 1,000 = 500 mcg. On the 2,500 mcg/mL vial, volume = 500 ÷ 2,500 = 0.20 mL = 20 units. Skipping the mg→mcg step is the classic ten-fold error.
Vial 10 mg = 10,000 mcg, water 3 mL. Concentration = 10,000 ÷ 3 ≈ 3,333 mcg/mL. A 500 mcg dose = 500 ÷ 3,333 ≈ 0.15 mL ≈ 15 units.
That 10 mg (10,000 mcg) vial at a 500 mcg dose yields 10,000 ÷ 500 = 20 doses — before accounting for dead space. Useful for working out how long a vial lasts and its cost per dose.
If ~0.05 mL stays in the needle hub each time and your dose is 0.10 mL, you lose roughly a third of the liquid per injection unless you account for it. On tiny peptide draws, dead space matters more than on a 1 mL draw.
Someone says “I draw 8 units.” On the 2,500 mcg/mL vial that is 8 ÷ 100 = 0.08 mL, × 2,500 = 200 mcg. On a 5,000 mcg/mL vial the same 8 units would be 400 mcg. The unit number alone never tells you the dose — you need the concentration too. See mg vs mcg vs mL vs units.
Honest caveats what this glossary is not
InjectBuddy is a maths tool, not a medical service. It does not validate a peptide's identity, purity, or whether using it is appropriate for you — it only converts between mass, volume and syringe units. Many research peptides such as BPC-157 and TB-500 are investigational and have no established human dose, so any number here is arithmetic for illustration, never a recommendation.
Correct maths can still be unsafe if handling is poor. Use clean technique, a fresh sterile needle and syringe, and the product's storage instructions. Bacteriostatic water carries benzyl alcohol and is not for use in neonates. Discard any vial that is cloudy, leaking, expired, or mislabelled.
So, what are the key peptide terms you need to know?
The handful of words that drive every peptide dose are lyophilized (freeze-dried powder), reconstitution (adding bacteriostatic water), concentration (mcg/mL after mixing), and the three measurement families: mass (mg and mcg), volume (mL), and syringe marks (U-100 units where 100 units = 1 mL). Once those are clear, the arithmetic reduces to two steps: concentration = total peptide divided by water added, then volume = dose divided by concentration, multiplied by 100 for the unit mark. Run your own numbers through the peptide reconstitution calculator to convert any vial and dose into the exact units to draw.
FAQs
What are the key peptide terms I need to understand dose math?
What does lyophilized mean on a peptide vial?
Is mcg the same as a syringe unit?
Does the glossary tell me what dose to take?
Why does more bacteriostatic water mean more units per dose?
Sources
- Hospira, Inc. Bacteriostatic Water for Injection, USP — prescribing information (0.9%–1.1% benzyl alcohol; not for use in neonates). DailyMed, FDA. DailyMed label.
- U.S. Pharmacopeia. General Chapter <797> Pharmaceutical Compounding — Sterile Preparations (beyond-use dating for reconstituted preparations). USP <797>.
- Centers for Disease Control and Prevention. Safe Injection Practices to Prevent Transmission of Infections to Patients. CDC injection safety guidance.
- Manchikanti L, et al. Assessment of infection control practices for interventional techniques: safe injection practices and single-dose vials. Pain Physician. 2012;15(5):E573–E614. PubMed PMID 22996856.
This guide is for general educational purposes only and does not constitute medical advice. InjectBuddy performs standard volume and ratio calculations from your inputs. Always follow your prescriber's specific instructions and confirm dosing with a qualified professional.