Dose-volume conversion: mg, mcg, mL, units
Converting between mg, mcg, mL, and insulin syringe units — the mcg vs mg trap, conversion table, and why writing units explicitly prevents 1000x errors.
Updated May 7, 2026 · 6 min read
Peptide dose conversion is where the most dangerous reconstitution errors happen. The units are small, similar-looking, and shift between mg and mcg depending on the peptide. A confusion between "0.25 mg" and "250 mg" is a 1000-fold dose error — the most consequential mistake possible in self-administered peptide use. This page is the reference for converting between mg, mcg, mL, and insulin syringe units, and a worked argument for why writing units explicitly is the only reliable safeguard.
The four units you need to know
| Unit | Definition | Used for |
|---|---|---|
| mg (milligram) | 1/1000 of a gram | Vial size; larger doses (BPC-157, TB-500, MOTS-c) |
| mcg (microgram) | 1/1000 of a mg | Smaller doses (ipamorelin, CJC, IGF-1 LR3) |
| mL (milliliter) | 1/1000 of a liter | Volume of solution after reconstitution |
| Unit | 0.01 mL on a U-100 syringe | What you read on the insulin syringe |
The relationships:
1 mg = 1000 mcg
1 mL = 1000 mcL = 100 units (on U-100 syringe)
1 unit = 0.01 mL = 10 mcL
Memorize these three. Every conversion is some combination of them.
The mcg vs mg trap
This is the single most-important safety distinction in peptide use. Different peptides are dosed at different scales:
| Peptide | Typical dose | Scale |
|---|---|---|
| BPC-157 | 250 mcg = 0.25 mg | mcg-scale (sometimes written in mg) |
| TB-500 | 2.5 mg | mg-scale |
| Ipamorelin | 200 mcg | mcg-scale |
| CJC-1295 (no DAC) | 100 mcg | mcg-scale |
| CJC-1295 with DAC | 1 mg = 1000 mcg | mg-scale |
| IGF-1 LR3 | 30 mcg | mcg-scale |
| MOTS-c | 5 mg | mg-scale |
| Tesamorelin | 1–2 mg | mg-scale |
| Sermorelin | 100–300 mcg | mcg-scale |
A user reading "250" without units could think:
- 250 mcg (correct for BPC-157)
- 250 mg (1000x overdose — would empty an entire 5 mg vial more than 50 times over)
The dose math reveals the absurdity, but only if you check it. A 250 mg dose at 2.5 mg/mL concentration would require 100 mL — 100 entire syringes. That's a clear "math doesn't work" signal. But intermediate confusions — say, 2.5 mg vs 0.25 mg — are 10x errors that don't trigger the same sanity check.
The safeguard: always write units explicitly. "Take your peptide" is ambiguous. "Take 250 mcg of BPC-157" is not.
Conversion table for common doses
| Dose | mg | mcg | mL at 2.5 mg/mL | Units (U-100) |
|---|---|---|---|---|
| 50 mcg | 0.05 mg | 50 mcg | 0.02 mL | 2 units |
| 100 mcg | 0.1 mg | 100 mcg | 0.04 mL | 4 units |
| 200 mcg | 0.2 mg | 200 mcg | 0.08 mL | 8 units |
| 250 mcg | 0.25 mg | 250 mcg | 0.1 mL | 10 units |
| 500 mcg | 0.5 mg | 500 mcg | 0.2 mL | 20 units |
| 1 mg | 1 mg | 1000 mcg | 0.4 mL | 40 units |
| 2.5 mg | 2.5 mg | 2500 mcg | 1.0 mL | 100 units |
| 5 mg | 5 mg | 5000 mcg | 2.0 mL | 200 units (2 syringes) |
The table assumes the standard reconstitution: 5 mg vial in 2 mL BAC water = 2.5 mg/mL. At different concentrations, the volume and unit columns shift proportionally.
Worked conversion examples
Example 1: dose stated in mcg, vial in mg
You have a 10 mg ipamorelin vial reconstituted in 2 mL BAC water. The protocol calls for 200 mcg twice daily.
Concentration: 10 mg ÷ 2 mL = 5 mg/mL
Convert dose to mg: 200 mcg = 0.2 mg
Volume: 0.2 mg ÷ 5 mg/mL = 0.04 mL
Units: 0.04 mL × 100 = 4 units on a U-100 syringe
Use a 30-unit syringe — 4 units is too small to read accurately on a 100-unit barrel.
Example 2: dose stated in mg, vial in mg
You have a 5 mg TB-500 vial reconstituted in 2 mL BAC water. The protocol calls for 2.5 mg twice weekly.
Concentration: 5 mg ÷ 2 mL = 2.5 mg/mL
Volume: 2.5 mg ÷ 2.5 mg/mL = 1.0 mL
Units: 1.0 mL × 100 = 100 units
That fills a 100-unit syringe completely. Reconstituting with 1 mL of BAC water instead would give 5 mg/mL, making the dose 0.5 mL = 50 units on a 50-unit syringe.
Example 3: very small dose
You have a 1 mg IGF-1 LR3 vial reconstituted in 2 mL BAC water. The protocol calls for 30 mcg.
Concentration: 1 mg ÷ 2 mL = 0.5 mg/mL
Convert dose: 30 mcg = 0.03 mg
Volume: 0.03 mg ÷ 0.5 mg/mL = 0.06 mL
Units: 0.06 mL × 100 = 6 units
Use a 30-unit syringe — 6 units is readable. If you wanted more volume per dose for accuracy, reconstitute with more water (3 mL → 0.33 mg/mL → 9 units; 4 mL → 0.25 mg/mL → 12 units).
Common conversion errors
| Error | What happens |
|---|---|
| Confusing mcg and mg | 1000x dose error — most dangerous |
| Misplacing a decimal | 10x dose error — still dangerous |
| Forgetting the ×100 in the units step | 100x under-dose — dose has no effect |
| Reading mL as units | 100x over-dose if you mistake "0.1 mL" for "0.1 units" |
| Calculating with wrong concentration | Off by whatever the concentration is wrong by |
The pattern: most errors are powers of 10. That's because the units are all power-of-10 relationships, so a slip moves the decimal. The defense is the same in every case — write units explicitly, sanity-check against the calculator, and verify volume falls in a reasonable range (5–100 units) before drawing.
The "always write units" rule
The single most-effective error-prevention practice:
| Don't write | Do write |
|---|---|
| "0.25" | "0.25 mg" or "250 mcg" |
| "Take 250" | "Take 250 mcg" |
| "2 mL water" → "200 mcg dose" | "2 mL water" → "200 mcg dose = 0.08 mL = 8 units" |
| "TB-500 dose: 2.5" | "TB-500 dose: 2.5 mg" |
In your protocol notes, your fridge label, your phone reminder, and your verbal protocol descriptions — write the unit every time. The five extra characters cost nothing. The error they prevent could be a 1000x overdose.
When the calculator is the answer
The reconstitution calculator handles all of this automatically:
- Enter vial size in mg
- Enter water volume in mL
- Enter target dose (in mg or mcg — the calculator handles either)
- Read concentration, volume, and unit count
- Validation flags catch unreasonable values (under 5 units, over 100 units, dose larger than vial)
For any dose you're not 100% confident on, run it through the calculator. The cost is 30 seconds. The benefit is eliminating an entire category of arithmetic error.