Instantly convert between micrograms (mcg) and milligrams (mg). Essential for accurate peptide dosing.
MCG to MG: Divide by 1,000. Example: 250 mcg ÷ 1,000 = 0.25 mg
MG to MCG: Multiply by 1,000. Example: 0.5 mg × 1,000 = 500 mcg
There is only one number to remember: 1 mg = 1,000 mcg. Everything else is moving a decimal point three places. Going from micrograms to milligrams moves it three places left, and going from milligrams to micrograms moves it three places right. If you can shift a decimal, you can do this conversion without the calculator above.
The confusion is not mathematical, it is a labeling mismatch. Research peptide vials are almost always labeled in milligrams, because that is how the lyophilized powder is weighed and sold. A vial says 5mg or 10mg. But published protocols, study literature, and dosing charts are frequently written in micrograms, because the amounts involved are small enough that milligrams produce awkward decimals. A protocol will say 250 mcg, not 0.25 mg.
So a single calculation routinely crosses two units. You are holding a vial labeled in mg, reading a protocol written in mcg, and drawing into a syringe marked in insulin units. Three different scales for one measurement. The conversion itself is trivial, but the opportunity to misplace a decimal is real, and the failure mode is not subtle: a decimal error here is a 1,000x error, not a 10% one.
This is also why the mcg and mg figures for the same dose look so different at a glance. A 250 mcg dose and a 0.25 mg dose are identical. If one of those numbers looks alarming and the other looks reasonable, that is a sign the units are worth double checking before anything else.
Example 1: protocol in mcg, vial in mg. A protocol lists 500 mcg. The vial is labeled 5 mg. Convert the dose first: 500 mcg ÷ 1,000 = 0.5 mg. Now both numbers are in the same unit, so the vial holds 5 ÷ 0.5 = 10 doses.
Example 2: converting to a syringe reading. A 5 mg vial reconstituted with 2 mL of bacteriostatic water gives 2.5 mg/mL. A 250 mcg target becomes 0.25 mg. Then 0.25 ÷ 2.5 = 0.1 mL, which is 10 units on a 1 mL insulin syringe, since 100 units = 1 mL.
Example 3: the decimal check. A protocol lists 1,500 mcg. That is 1.5 mg, not 15 mg and not 0.15 mg. A useful sanity check is that the mg figure should always be the smaller of the two numbers. If your milligram result came out larger than your microgram figure, the decimal moved the wrong way.
Confusing mcg with mg on the vial label. Some labels abbreviate micrograms as µg rather than mcg. They mean the same thing. The Greek letter mu is the formal symbol, and mcg is the plain-text substitute used to avoid character issues.
Confusing milligrams with milliliters. These are different kinds of measurement entirely. Milligrams are mass, the amount of peptide. Milliliters are volume, the amount of liquid. A 5 mg vial does not contain 5 mL of anything until you add water, and the relationship between the two is set by how much water you add.
Treating syringe units as a dose. Insulin syringe units measure volume, not peptide. On a 1 mL syringe, 1 unit is 0.01 mL. What that volume contains depends entirely on your concentration, which is why the same 10 unit draw can be 250 mcg in one vial and 500 mcg in another.
Rounding too early. Convert first, then round at the end. Rounding a concentration before dividing compounds the error into the final syringe reading.
Related tools: reconstitution calculator, insulin syringe units to mL, and the peptide half-life chart.
Need to calculate a full peptide dose? Use our reconstitution calculator →