Peptide Dosage Calculator: Units, mL and Vial Math

Fourteen calculators sit behind this page. Find the row that matches the question in your head, then go straight to that tool.

Most people arrive needing two of these in sequence. The reconstitution calculator turns a dry vial into a concentration and a unit count. A compound-specific calculator such as the BPC-157 dosage calculator or the tirzepatide dosage calculator tells you which dose to feed it.

The rest of this page teaches the arithmetic those tools run. Learn it once and you can check any calculator's output, including ours.

The peptide inside a lyophilized vial is a fixed quantity. A vial labeled 5 mg holds 5 mg of powder whether you dissolve it in 1 mL of water or in 5 mL.

Think of a spoonful of salt. Stir it into a shot glass and a single drop is brutally salty. Stir the same spoonful into a jug and a single drop barely registers. The salt never changed. The water did.

Concentration is the amount of peptide per unit of liquid, written as mg/mL. Adding more bacteriostatic water lowers the concentration, so each unit on the syringe carries less peptide, so you draw more units for the same dose. The dose stays constant. The volume that delivers it does not.

This is why "how many units is my dose" has no answer until someone names the vial strength and the water volume. Two people injecting the same 250 mcg can correctly draw 10 units and 25 units, because one reconstituted at 2.5 mg/mL and the other at 1 mg/mL.

Choosing the water volume is a convenience decision, not a safety one. More water means larger, easier-to-read unit counts and less rounding error. Less water means a smaller injection volume. The peptide reconstitution calculator will show you both, and how to reconstitute a peptide covers the physical technique.

Here is the chain end to end, using a 5 mg vial, 2 mL of bacteriostatic water, and a 250 mcg dose.

1. 1.Read the vial strength. The label says 5 mg. That is the total peptide in the vial, not a per-dose amount.

1. 1.Choose the water volume and add it. You add 2 mL of bacteriostatic water, aiming the stream at the glass wall rather than at the powder. Whether that solvent is the same thing as reconstitution solution is a fair question, answered in is reconstitution solution the same as bacteriostatic water.

1. 1.Calculate concentration. 5 mg ÷ 2 mL = 2.5 mg/mL. Write this on the vial with a marker. Six weeks later you will not remember it.

1. 1.Convert the dose to milligrams. 250 mcg ÷ 1000 = 0.25 mg. Micrograms and milligrams differ by a factor of 1,000, and this is where the largest errors enter. The peptide unit converter does this step if you want a second opinion.

1. 1.Calculate the volume to draw. 0.25 mg ÷ 2.5 mg/mL = 0.1 mL.

1. 1.Convert volume to units. A U-100 syringe reads 100 units per 1 mL, so one unit is 0.01 mL. 0.1 mL × 100 = 10 units.

1. 1.Sanity-check with the shortcut. On a U-100 syringe, one unit carries the concentration in mg/mL multiplied by 10, expressed in mcg. At 2.5 mg/mL, one unit is 25 mcg. 250 ÷ 25 = 10 units. The two routes agree.

1. 1.Check how many doses the vial holds. 5 mg ÷ 0.25 mg = 20 doses. If you draw the vial dry at 12 doses, one of your numbers was wrong.

That is the whole method. Every compound-specific tool on this site, from the semaglutide dosage calculator to the IGF-1 LR3 dosage calculator, runs exactly these eight lines with the dose pre-filled.

Scenario 1: a U-40 syringe read as a U-100 syringe. Your calculator says 10 units. On a U-100 barrel that is 0.1 mL. Pull to the 10 mark on a U-40 barrel and you have drawn 0.25 mL, because a U-40 syringe puts only 40 units in a milliliter. At 2.5 mg/mL that syringe now holds 625 mcg instead of 250 mcg, exactly 2.5 times the intended dose. The 5 mg vial that should have lasted 20 injections empties after 8. U-40 syringes exist for veterinary insulin and turn up in cheap online kits. The fix: read the barrel print. If it does not say U-100, do not use it for a U-100 calculation.

Scenario 2: 1 mL of bacteriostatic water instead of 2 mL. The 5 mg vial is now 5 mg/mL, not 2.5 mg/mL. Draw the 10 units your calculator gave you and you inject 0.1 mL of a double-strength solution: 500 mcg instead of 250 mcg. Nothing looks wrong. The liquid is clear, the syringe looks identical, the injection feels the same. Every dose for the life of that vial is doubled, and the vial runs dry after 10 injections rather than 20. The fix: measure the water into the syringe before you add it, and write the resulting mg/mL on the vial label.

Scenario 3: counting lines on a 1 mL barrel. A 0.5 mL insulin syringe is usually marked in 1-unit increments. A 1 mL insulin syringe is usually marked in 2-unit increments. Count ten lines up from zero on the 1 mL barrel and you are at 20 units, not 10. At 2.5 mg/mL that is 500 mcg instead of 250 mcg, a doubled dose from a single misread. The fix: read the printed numbers, never the line count, and check the increment before the first draw.

None of these errors announces itself at the moment it happens. They surface later as an unexpectedly empty vial or a side-effect profile that does not match the protocol. Cross-check your volume against the peptide reconstitution calculator before the first injection, and read how to inject peptides for the handling steps around it.

The number printed on an insulin syringe is a unit count, not a volume. What that unit means depends entirely on the syringe's calibration, and the calibration is printed on the barrel or the wrapper.

U-100. 100 units per 1 mL. One unit is 0.01 mL. This is the standard for human insulin and the assumption behind every peptide calculator on this site, including the retatrutide dosage calculator and the TB-500 dosage calculator.

U-40. 40 units per 1 mL. One unit is 0.025 mL, two and a half times the U-100 unit. Sold for veterinary insulin. A U-100 unit count executed on a U-40 barrel delivers 2.5 times the dose.

U-500. 500 units per 1 mL. One unit is 0.002 mL, one fifth of the U-100 unit. Used for concentrated insulin. A U-100 unit count executed on a U-500 barrel delivers one fifth of the dose.

There is no such thing as a "U-50" calibration, and this is the single most common misunderstanding of the syringe. What people call a U-50 is a 50-unit barrel, a U-100 syringe with a 0.5 mL capacity. Barrel capacity and calibration are different properties. U-100 syringes are sold in three common sizes:

All three are U-100. All three make one unit equal 0.01 mL. The only thing that changes is how much they hold and how finely they are marked. For doses under 30 units, a 0.3 mL barrel gives you the most readable markings and the smallest rounding error.

Two habits make the reading reliable. Measure to the leading edge of the rubber stopper, the flat face nearest the needle, not the pointed tip behind it. And hold the barrel at eye level, because looking down at a syringe on a table introduces a parallax error of several units on a 1 mL barrel.

Find your vial strength in the left column and the water you plan to add across the top. The cell is your concentration in mg/mL.

Now convert that concentration into what one unit actually delivers on a U-100 syringe. Multiply the mg/mL by 10 and the answer is in micrograms.

And the table most people want: units to draw on a U-100 syringe for a given dose at a given concentration.

Cells reading "over 1 mL" mean the dose exceeds the capacity of a standard 1 mL insulin syringe at that concentration. Reconstitute with less water, or split the injection. For GLP-1 vials specifically, the semaglutide mixing chart and tirzepatide dosage chart in units carry the same math with the doses filled in.

Bacteriostatic water is sterile water with 0.9% benzyl alcohol added as a preservative, which is what allows repeated needle entries into the same vial. Sterile water has no preservative and is single-use once punctured. The difference is covered in bacteriostatic water vs sterile water.

Benzyl alcohol is not inert. It caused fatal metabolic acidosis and respiratory collapse in premature neonates exposed to benzyl alcohol-preserved flush solutions, the episode that named "gasping syndrome" (Gershanik et al., N Engl J Med, 1982). Adult exposures from a 2 mL vial are orders of magnitude smaller, but the preservative is a drug, not water.

It also interacts with the peptide. Benzyl alcohol increased aggregation of a reconstituted lyophilized protein formulation in a controlled study, an effect that scaled with alcohol concentration (Roy et al., J Pharm Sci, 2005). Aggregation removes active peptide from solution, which is one reason an old vial can feel weaker than a fresh one at the same calculated dose.

Peptides in aqueous solution degrade continuously through hydrolysis, deamidation, oxidation and aggregation, and the rate climbs with temperature (Manning et al., Pharm Res, 2010). Refrigeration slows the clock but does not stop it, which is the physical basis for the shelf-life numbers in how long do reconstituted peptides last and the handling rules in how to store peptides.

None of this changes the arithmetic. Concentration is still mg divided by mL on the day you mix. It changes how much of that calculated dose is still intact peptide eight weeks later.

Mistake 1: treating mcg and mg as interchangeable. A 1,000-fold error is the easiest one to make and the hardest to survive, since 0.25 mg and 250 mcg look nothing alike on paper but are identical. The fix: convert everything to milligrams before dividing, and verify with the peptide unit converter.

Mistake 2: recalculating from memory after a new vial. Vial strengths change between batches and suppliers. A 10 mg vial reconstituted with the 2 mL you used on a 5 mg vial gives 5 mg/mL, and your old unit count now delivers double. The fix: rerun the peptide reconstitution calculator for every new vial, then write the concentration on the label.

Mistake 3: over-correcting for the powder's volume. The lyophilized cake does occupy space, so 2 mL of water into a 5 mg vial yields marginally more than 2 mL of solution. At typical peptide masses that displacement is well under 1% of the total, smaller than the rounding error on a 1 mL barrel marked in 2-unit steps. The fix: add the full water volume the calculator specifies and never shave it down to "correct" for the powder.

Mistake 4: stacking two peptides in one syringe without checking. Combining compounds changes nothing about each one's concentration, but it does change compatibility and timing. The fix: verify the pairing in the peptide interaction checker, build the week in the peptide stack calculator, and read the peptide stacking guide before you draw anything.