Here's the question almost everyone asks on their first vial, usually written down somewhere in a panic: "Is the total in mg the dose I'm taking, or the concentration?" It's the right question, because the whole problem lives in that one confusion. Three different scales are in play — milligrams, micrograms, and units — and they aren't even the same kind of measurement.

The number on the vial is the total, not your dose

A vial labelled 5 mg contains 5 mg of peptide in total. That is the whole supply, not one injection. Your dose is a small slice of it — maybe 250 mcg — which you'll draw over and over until the vial runs out. Reading the vial's total as your dose is a twenty-fold error waiting to happen.

A 5 mg vial is not a 5 mg dose. It's the source. If each dose is 250 mcg, that single vial holds twenty of them.

Milligrams and micrograms: a factor of 1000

These two are the easy pair — they measure the same thing (mass), just at different sizes:

1 mg = 1000 mcg

So 0.25 mg is 250 mcg, and 5 mg is 5000 mcg. The trap is that vials are labelled in mg while doses are often written in mcg, so you're constantly sliding the decimal point three places. Get that slide wrong and you're out by a thousand.

Units are a different animal entirely

Here's the part that catches people. A unit is not an amount of peptide. It's a mark on the syringe measuring volume. On a U-100 insulin syringe:

100 units = 1 ml, so 1 unit = 0.01 ml

A unit tells you how much liquid you've drawn — it says nothing about how much drug is in that liquid. What fills the gap is the concentration, which you set when you chose how much water to add. That's why the same dose can be a different number of units in two different vials.

So how many units is 250 mcg?

The honest answer is: it depends on your concentration, and anyone who gives you a fixed number without asking hasn't understood the question. Watch the same 250 mcg dose move as the water changes:

250 mcg, three different mixes:

  • 5 mg in 1 ml → 5 mg/ml → 5 units
  • 5 mg in 2 ml → 2.5 mg/ml → 10 units
  • 5 mg in 4 ml → 1.25 mg/ml → 20 units

Same peptide, same dose, three different marks on the barrel. This is exactly why you can't memorise "my dose is N units" — the moment you reconstitute a vial with a different amount of water, N changes.

The one order that always works

Whenever you're unsure, run the scales in this order and the confusion disappears:

  1. Put the vial total and your dose in the same unit (convert mcg ↔ mg).
  2. Divide the total by the water to get concentration (mg/ml).
  3. Divide your dose by the concentration to get volume (ml).
  4. Multiply the volume by 100 to get units on a U-100 syringe.
This article is general educational information about arithmetic. It is not medical advice and not a dosing recommendation. Vialog does not tell you what dose to take. Always consult a qualified healthcare professional.

Don't slide the decimal by hand.

Vialog keeps mg, mcg and units straight for you, shows every step, and refuses any number your syringe can't draw.

See Vialog — coming soon

Frequently asked

Is the number on the vial the dose I take?

No. It's the total in the whole vial — the source you draw many doses from. Your dose is a fraction of it.

How many mcg are in a milligram?

1000. So 250 mcg is 0.25 mg, and 5 mg is 5000 mcg.

Is 1 mg equal to 100 units?

Only if the concentration happens to be exactly 1 mg/ml. Units measure volume, not mass — the same milligram can be 50, 100 or 200 units depending on the water.

What is a unit on an insulin syringe?

A volume graduation. On a U-100 syringe, 100 units is 1 ml, so one unit is 0.01 ml. The concentration decides how much peptide sits in that volume.

Keep reading: How many units do I draw? A worked BPC-157 example.