PepEasyWiki

How Dosing Calculators Work

Once a vial is reconstituted, a dosing calculator handles the day-to-day question: given my concentration, how much liquid equals the dose I want? This page explains the concentration math and unit conversions behind that — purely educational, no live tool.

Concentration is the key number

After mixing, every peptide solution has a concentration — how much peptide sits in each millilitre of liquid:

concentration (mg/mL) = peptide amount (mg) ÷ liquid volume (mL)

A 10 mg vial in 2 mL water is 5 mg/mL. The same 10 mg vial in 1 mL is 10 mg/mL. The peptide amount is fixed; the water you chose sets the concentration, and the concentration is what every dosing calculation depends on.

mcg ↔ mg conversions

Doses for many peptides are quoted in micrograms, while vials are labelled in milligrams. The only conversion you need:

1 mg = 1000 mcg
mcg → mg : divide by 1000
mg → mcg : multiply by 1000

Examples: 250 mcg = 0.25 mg; 1.5 mg = 1500 mcg. Getting this wrong by a factor of 1000 is the single most dangerous error in peptide dosing, so always convert your dose and your concentration into the same unit before dividing.

Mapping a desired dose to volume drawn

With dose and concentration in matching units:

volume to draw (mL) = desired dose ÷ concentration

To express that on a U-100 insulin syringe (100 units = 1 mL):

units to draw = volume to draw (mL) × 100

Worked example

Vial 10 mg, reconstituted in 2 mL, desired dose 500 mcg.

  1. Concentration: 10 mg ÷ 2 mL = 5 mg/mL = 5000 mcg/mL
  2. Match units — work in mcg. Desired dose = 500 mcg.
  3. Volume: 500 mcg ÷ 5000 mcg/mL = 0.1 mL
  4. Units: 0.1 mL × 100 = 10 units

So a 500 mcg dose from this vial is 10 units, and the vial provides 10,000 ÷ 500 = 20 doses.

Changing the dose, not the vial

Because volume scales linearly with dose, once you know one point you can scale the rest. At 5000 mcg/mL: 250 mcg → 5 units, 500 mcg → 10 units, 1000 mcg → 20 units. Doubling the dose doubles the units.

GLP-1 and "click" pens are different

Branded GLP-1 products like Semaglutide and Tirzepatide often come in fixed-dose pens measured in mg per click or per injection, not insulin units. The concentration logic is the same, but read the device’s own instructions rather than applying U-100 unit math.

For the full reconstitution workflow and concentration charts, see Reconstitution & Dosing Math.

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Educational information only — not medical advice. See Disclaimer.

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