Understanding Peptide Units: mg, mcg, mL, IU — How to Convert Without Mistakes

The single most common peptide mistake isn't medical — it's mathematical. People drop a decimal, confuse milligrams with micrograms, or misread an insulin syringe and end up with a dose that's off by 10x. This guide is the unit reference you should keep open the first ten times you reconstitute a vial.

The four units you'll meet

Unit	What it measures	Where it shows up
mg (milligram)	Mass of peptide	Vial labelling (e.g., "5 mg BPC-157")
mcg (microgram)	Mass of peptide	Research dosing (e.g., "250 mcg")
mL (milliliter)	Volume of solution	Bacteriostatic water and reconstituted solution
IU (International Unit)	Biological activity	HGH, HCG, insulin

The conversion you'll do constantly

1 mg = 1,000 mcg

Memorize this. It's the conversion that catches most people because the difference between 250 mcg and 0.25 mg is just notation, but the difference between 250 mcg and 2.5 mg is a 10x overdose.

Examples:

• 5 mg vial = 5,000 mcg
• 250 mcg dose = 0.25 mg
• 0.1 mg = 100 mcg

Volume vs mass: the role of mL

mg and mcg measure mass (how much peptide). mL measures volume (how much liquid). They are not interchangeable.

A vial labelled "5 mg BPC-157, 2 mL" has 5 mg of peptide dissolved in 2 mL of liquid. The concentration is 5 mg ÷ 2 mL = 2.5 mg/mL = 2,500 mcg/mL.

Concentration is the bridge between mass and volume. The reconstitution math always works the same way:

concentration (mcg/mL) = vial size (mcg) ÷ diluent volume (mL)
volume to draw (mL)    = dose (mcg) ÷ concentration (mcg/mL)

The PeptideHub calculator does this automatically — but you should be able to do it in your head.

Insulin syringe units: the practical unit you draw

Insulin syringes are calibrated in units, not mL. The relationship depends on the syringe type:

Syringe	Units per mL	Total units (1 mL)	Total units (0.5 mL)
U-100	100	100	50
U-40 (less common)	40	40	—

So on a U-100 syringe:

• 1 unit = 0.01 mL
• 10 units = 0.10 mL
• 100 units = 1.00 mL

When the calculator says "draw 10 units," it means fill the syringe to the 10-unit mark — equivalent to 0.10 mL.

IU: when it applies, when it doesn't

International Units (IU) measure biological activity, not mass. Different compounds have different IU-to-mass relationships:

• HGH (human growth hormone): approximately 333 mcg = 1 IU (1 mg ≈ 3 IU)
• HCG (human chorionic gonadotropin): IU is the standard unit
• Insulin: 1 IU ≈ 36 mcg (different definition, derived from biological standard)
• Most research peptides (BPC-157, TB-500, CJC-1295, etc.): do not use IU

For peptides that don't have a defined IU standard, dosing is always in mg or mcg. If you see "IU" on a peptide that isn't HGH, HCG, or insulin, double-check the source — it may be incorrect labeling.

The PeptideHub calculator lets you input dose in mcg, mg, or IU, and asks for the mcg-per-IU ratio when you switch to IU, since that ratio is compound-specific.

The worked example

You have a 5 mg vial of BPC-157. You reconstitute with 2 mL of bacteriostatic water. You want to dose 250 mcg twice daily.

1. Total peptide mass: 5 mg × 1000 = 5,000 mcg
2. Concentration: 5,000 mcg ÷ 2 mL = 2,500 mcg/mL
3. Per unit (U-100 syringe): 2,500 mcg/mL ÷ 100 units/mL = 25 mcg/unit
4. Units to draw for 250 mcg: 250 ÷ 25 = 10 units
5. Doses per vial: 5,000 mcg ÷ 250 mcg = 20 doses
6. Days per vial (at 2× daily): 20 ÷ 2 = 10 days

The calculator runs all six lines in real-time.

Common unit mistakes

Mixing mg and mcg

Calling a 250 mcg dose "250 mg" — or vice versa — is a 1000x error. Always write mcg (microgram) or mg (milligram) explicitly. Never abbreviate μg to ug or mg casually.

Reading the wrong syringe line

A U-100 1 mL syringe has 100 unit marks. Some users confuse the 10-unit mark with the 100-unit mark when the syringe is at arm's length. Solution: use 0.5 mL syringes when possible — fewer marks, less confusion.

Confusing diluent volume with dose volume

The 2 mL you added to the vial is the diluent volume. The 0.1 mL you draw for a dose is the dose volume. They aren't the same number.

Forgetting to convert vial mg to mcg

The vial says "5 mg" but research doses are in mcg. The calculator handles this for you, but if you're doing it by hand: always multiply vial mg by 1000 first.

Wrong syringe type

A U-40 syringe reads units differently from U-100. If you mix them up, your "20-unit" dose could be either 0.20 mL or 0.50 mL — a 2.5x error. Always verify your syringe type.

Quick reference table

For a 5 mg vial at different reconstitution volumes, on a U-100 syringe:

Diluent	Concentration	100 mcg	250 mcg	500 mcg	1 mg
1 mL	5,000 mcg/mL	2 u	5 u	10 u	20 u
2 mL	2,500 mcg/mL	4 u	10 u	20 u	40 u
3 mL	1,667 mcg/mL	6 u	15 u	30 u	60 u
5 mL	1,000 mcg/mL	10 u	25 u	50 u	100 u

For other vial sizes or doses, use the calculator.

Next steps

• Open the calculator — practice with your actual vial and dose.
• Read the reconstitution guide for the mixing process.
• Bookmark the peptide profiles for per-peptide dose ranges.