Peptide Measurement Guide: Converting mg, mcg, mL, IU, and Syringe Units

Disclaimer: This guide is for research and educational purposes only. It is not medical advice. Research peptides are not approved by the FDA for human use. Consult a licensed healthcare professional before using any injectable compound.

Peptide measurement involves multiple overlapping unit systems. Vials are labeled in milligrams. Doses are expressed in micrograms. Syringes are marked in units or milliliters. Growth hormone introduces International Units. Getting these conversions wrong by even one decimal place can mean a 10x or 1,000x dosing error.

This guide is a complete reference for all units used in peptide research and how to convert between them.

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The Measurement Problem

When you purchase a research peptide, you might encounter a vial labeled "5 mg BPC-157." Your protocol might specify a dose of "250 mcg." Your syringe is marked in units. These three numbers exist in three different unit systems, and you must correctly convert between all of them to draw the right amount.

A researcher who confuses mg with mcg will draw 1,000 times the intended dose. A researcher who uses a U-40 syringe while calculating for U-100 will deliver 2.5 times the intended dose. These are not small rounding errors — they are the kind of mistakes the calculator was built to prevent.

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The Metric System for Peptides

Peptide mass is measured in metric weight units:

Unit	Symbol	Equivalence
Gram	g	Base unit
Milligram	mg	1 mg = 0.001 g = 1/1,000 g
Microgram	mcg (or µg)	1 mcg = 0.001 mg = 1/1,000,000 g
Nanogram	ng	1 ng = 0.001 mcg (rarely used in dosing)

The relationship you will use constantly:

1 mg = 1,000 mcg

This means a 5 mg vial contains 5,000 mcg of peptide. A 2 mg vial contains 2,000 mcg. If your dose is 250 mcg, a 5 mg vial provides 20 doses.

Converting mcg to mg and back

• To convert mg to mcg: multiply by 1,000
  • 5 mg x 1,000 = 5,000 mcg
• To convert mcg to mg: divide by 1,000
  • 250 mcg / 1,000 = 0.25 mg

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Volume: Milliliters (mL)

Volume is measured in milliliters for liquid measurements:

Unit	Equivalence
1 mL	1 cc (cubic centimeter) — these are identical
0.1 mL	100 microliters (µL)
0.01 mL	10 microliters

When you reconstitute a peptide vial, you add a specific volume of BAC water. This volume, combined with the peptide mass, determines the concentration of the solution.

Concentration formula: Concentration (mcg/mL) = Total peptide (mcg) / Volume of diluent added (mL)

Example: 5 mg (5,000 mcg) BPC-157 + 2 mL BAC water = 2,500 mcg/mL

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Syringe Unit Systems: U-100 and U-40

Insulin syringes do not display milliliters on most scales — they display units. The unit scale depends on which syringe type you have.

U-100 (standard for peptide research)

A U-100 syringe holds 100 units per mL. Therefore:

• 1 unit = 1/100 mL = 0.01 mL
• 10 units = 0.10 mL
• 50 units = 0.50 mL
• 100 units = 1.00 mL

U-40 (avoid unless protocol specifies)

A U-40 syringe holds 40 units per mL. Therefore:

• 1 unit = 1/40 mL = 0.025 mL
• 10 units = 0.25 mL
• 40 units = 1.00 mL

If you use a U-40 syringe but calculate assuming U-100, you will draw 2.5 times more liquid than intended. All PepComputer calculators and reference materials assume U-100 unless stated otherwise.

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International Units (IU): The HGH Context

International Units (IU) are a measurement of biological activity rather than mass. They are not directly equivalent to mcg without a compound-specific conversion factor.

IU is primarily used for Human Growth Hormone (HGH)

The relationship for synthetic HGH is: 1 IU of HGH = approximately 333 mcg = 0.333 mg

Or equivalently: 1 mg of HGH = approximately 3 IU

This conversion is specific to HGH and does not apply to other peptides. It exists because HGH potency was historically measured by biological effect before mass-based measurements became standard.

Most research peptides are NOT dosed in IU

BPC-157, TB-500, CJC-1295, ipamorelin, semaglutide, GHK-Cu, and virtually all other research peptides are dosed in mcg or mg. If you see an IU dose for one of these compounds in a protocol, question the source — it is likely an error.

The IU conversion calculator handles HGH-specific conversions.

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Complete Conversion Reference Table

Starting unit	Target unit	Operation
mg	mcg	Multiply by 1,000
mcg	mg	Divide by 1,000
mL	U-100 units	Multiply by 100
U-100 units	mL	Divide by 100
mL	U-40 units	Multiply by 40
U-40 units	mL	Divide by 40
IU (HGH)	mcg	Multiply by 333
mcg (HGH)	IU	Divide by 333
mg (HGH)	IU	Multiply by 3
IU (HGH)	mg	Divide by 3

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Step-by-Step Calculation Walkthrough

Here is the complete process for converting a vial and dose specification to syringe units.

Given information:

• Vial size: 5 mg
• BAC water added: 2 mL
• Desired dose: 300 mcg
• Syringe type: U-100

Step 1: Convert vial size to mcg 5 mg x 1,000 = 5,000 mcg in the vial

Step 2: Calculate concentration 5,000 mcg / 2 mL = 2,500 mcg/mL

Step 3: Convert dose to volume (mL) 300 mcg / 2,500 mcg/mL = 0.12 mL

Step 4: Convert volume to U-100 units 0.12 mL x 100 = 12 units

Draw to the 12-unit line on your U-100 syringe.

Verification: 12 units x 0.01 mL/unit = 0.12 mL. 0.12 mL x 2,500 mcg/mL = 300 mcg. Correct.

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Common Errors and How to Avoid Them

Error 1: Treating mg and mcg as the same

A dose of 0.25 mg equals 250 mcg — not 0.25 mcg. Always confirm which unit is being referenced. Protocols typically use mcg; vials are labeled in mg.

Error 2: Forgetting to convert vial size before calculating concentration

If your vial is 5 mg and you add 2 mL of BAC water, the concentration is 2,500 mcg/mL (not 5/2 = 2.5 with unclear units). Always work in consistent units throughout the calculation.

Error 3: Wrong syringe type

A 10-unit draw on a U-40 syringe delivers 0.25 mL, while a 10-unit draw on a U-100 syringe delivers 0.10 mL. These are not the same. Confirm syringe type before every calculation.

Error 4: Applying IU conversion to non-HGH peptides

IU is not a general unit for research peptides. If you see a "3 IU" dose for BPC-157, that is almost certainly an error in the source material.

The PepComputer calculator handles all of these conversions automatically and flags common input errors.

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Frequently Asked Questions

Q: Is mcg the same as µg? Yes. "mcg" and "µg" both mean microgram. "mcg" is the preferred notation in medical and research documentation because the µ symbol can be misread.

Q: My protocol lists the dose in mg, but the calculator asks for mcg. What do I enter? Convert first: multiply the mg value by 1,000 to get mcg. Then enter the mcg value. For example, 0.25 mg = 250 mcg.

Q: What if I do not know how much BAC water was added to my vial? You cannot accurately calculate a dose without knowing the concentration. If you added the BAC water yourself, use the volume you added. If you received a pre-reconstituted vial, contact the supplier for the concentration. Never estimate.

Q: Does water volume change when you add a small amount of peptide powder? The lyophilized powder displaces negligible volume. For practical purposes, the volume of the reconstituted solution equals the volume of BAC water added. This is the assumption used in all standard calculations.

Q: Can I use the unit conversion calculator for any peptide? Yes. The unit conversion calculator handles mg/mcg/mL/unit conversions for any compound. The IU calculator is specific to HGH.