Retatrutide Dosage Calculator

Concerned about side effects? See Retatrutide side effects — what the research documents (honest, sourced, research-use-only).

The retatrutide dosage calculator on this page turns the two numbers you actually know — how many milligrams are in your vial and how many milliliters of bacteriostatic water you added — into the one number your syringe actually shows: units. Retatrutide is dosed in milligrams, but a U-100 insulin syringe is marked in units, so every reconstituted peptide requires a quick conversion before you can measure a dose accurately. The math is deterministic and universal, and this tool applies it the same way a pharmacist would. Enter your vial size, your water volume, and your target milligram dose, and you get the concentration, the exact draw volume, the retatrutide units per dose to pull to on the barrel, and how many doses the vial holds.

Why a retatrutide dosage calculator matters

Retatrutide ships as a lyophilized (freeze-dried) powder. In that form it has a mass but no volume you can draw — you cannot pull “2 mg” out of a dry vial. Reconstitution dissolves the powder into a known volume of bacteriostatic water, which creates a liquid of a specific concentration (milligrams per milliliter). Only then does a milligram target map onto a physical distance on the syringe. Because retatrutide is one of the more potent compounds in the incretin class and is titrated in small milligram steps, a rounding slip between milligrams, milliliters, and units is the single most common source of a mismeasured dose. The calculator removes the guesswork by doing the same four calculations every time, with no mental arithmetic.

How reconstitution works

Reconstitution is simply mixing a fixed mass of powder with a fixed volume of liquid. The powder amount is printed on the vial (for example, 10 mg). The liquid is bacteriostatic water — sterile water with a small amount of benzyl alcohol that inhibits microbial growth, which is what allows a multi-dose vial to be used over several weeks when refrigerated. You add the water slowly down the inside wall of the vial, let the powder dissolve without vigorous shaking, and the result is a clear solution. The mass never changes; you are only choosing how much liquid to spread it across. Add less water and the solution is more concentrated (fewer units per dose); add more water and it is more dilute (more units per dose, easier to read small steps). The reconstitution volume is a choice, and the calculator shows you the consequences of that choice instantly.

The math behind the retatrutide dosage calculator

Four formulas do all the work. They are exact, they never change, and you can check the tool against them by hand:

• Concentration (mg/mL) = vial mg ÷ bacteriostatic water mL
• Draw volume (mL) = target dose mg ÷ concentration
• Units on a U-100 syringe = draw volume mL × 100
• Doses per vial = floor(vial mg ÷ dose mg)

The only unit trick worth memorizing: a U-100 syringe has 100 units per milliliter, so 1 unit = 0.01 mL. That is why the “× 100” step converts a draw volume straight into the mark you pull to. And when a protocol is written in micrograms, convert first — 250 mcg is 0.25 mg, and 500 mcg is 0.5 mg — before putting it into the dose field.

Worked example: 10 mg vial, 2 mL water, 2 mg dose

Here is the calculation using real values from this site’s catalog — a 10 mg retatrutide vial reconstituted with 2 mL of bacteriostatic water, targeting a 2 mg dose, measured on a U-100 insulin syringe:

1. Concentration = 10 mg ÷ 2 mL = 5 mg/mL
2. Draw volume = 2 mg ÷ 5 mg/mL = 0.4 mL
3. Units = 0.4 mL × 100 = 40 units
4. Doses per vial = floor(10 mg ÷ 2 mg) = 5 doses

Notice how clean the reading is: at this concentration, every 0.5 mg of dose equals exactly 10 units, so the whole titration ladder lands on round marks. That is the practical reason many people choose 2 mL of water for a 10 mg vial — it makes the syringe easy to read.

How much bacteriostatic water should you add?

There is no single “correct” reconstitution volume — it is a trade-off, and the calculator lets you audition volumes in seconds. Two guardrails keep the choice sensible:

• The water has to physically fit the vial. Small peptide vials are typically 3 mL glass, so 1–2 mL of water is the practical ceiling for the smaller sizes. Do not plan a 5 mL fill for a vial that only holds 3 mL.
• Aim for round, readable units. If your dose lands on an awkward number like 33.3 units, the reading error at the syringe outweighs any theoretical benefit. Nudging the water volume to make doses land near 10, 20, 25, 40, or 50 units is worth doing.

A common, readable convention is to match water volume to the dose ladder so that low starting doses still register as a measurable number of units rather than a sliver near the needle. For a 10 mg vial, 1 mL gives 10 mg/mL (compact, small draws) while 2 mL gives 5 mg/mL (roomier, easier to read low doses) — same total drug either way.

Reading retatrutide units per dose on a U-100 syringe

A U-100 insulin syringe is marked from 0 to 100 units over 1 mL. Each numbered line is usually 10 units; the small ticks between them are 1 or 2 units depending on the syringe. To measure a dose, pull the plunger until the top edge of the black stopper (the side nearest the needle) sits on your target unit line — 40 units in the worked example above. Read at eye level to avoid parallax. Because “units” already bakes in the concentration, you never convert at the bedside: the calculator gives you a unit number, and you pull to it. That is the entire benefit of thinking in retatrutide units per dose instead of milliliters.

Matching the syringe barrel to your unit reading

Insulin syringes come in more than one barrel size, and the unit figure from the calculator tells you which one to reach for. A 1 mL barrel reads 0 to 100 units, a 0.5 mL barrel reads 0 to 50 units, and a 0.3 mL barrel reads 0 to 30 units — all on the same U-100 scale, so a “40 units” result means the same physical volume of liquid on any of them. The narrower barrels simply spread those units over a longer plunger travel, so each printed tick sits farther apart and is easier to line up on. If your worked-example dose is 40 units, a 0.5 mL syringe would place it about four-fifths of the way up the barrel — well within range and clearly readable. If instead you were drawing only 13 units — the 2 mg reading from a 30 mg vial in the table below — a 0.3 mL barrel would render that small dose far more precisely than the crowded low end of a 1 mL barrel. The rule of thumb: pick the smallest barrel that still comfortably holds your unit number, and the same 100-units-per-mL math the calculator uses stays valid on all of them.

Vial-size reference at 2 mL of water

This site stocks retatrutide in several vial sizes. The table below shows what each size becomes when reconstituted with 2 mL of bacteriostatic water, using the same 2 mg reference dose so you can compare. Change the water volume in the calculator to see any other combination.

The pattern is worth internalizing: at a fixed water volume, a larger vial is more concentrated, so the same dose is drawn to a smaller unit number. Larger vials also stretch to more doses, but the smaller unit reading leaves less room for a precise low-dose measurement — which is exactly why some people pair a larger vial with more water.

A titration ladder for the worked-example vial

Retatrutide is a once-weekly subcutaneous compound that is titrated upward over time rather than started at a full dose. Using the worked example’s 5 mg/mL solution (10 mg vial in 2 mL), here is how a rising milligram ladder maps to units — every value confirmed against the four formulas:

This is a mapping table, not a schedule. For the documented titration steps, intervals, and ceilings actually used in the research, see the single-peptide dosage protocol page.

Mistakes the calculator catches

• Confusing milliliters with units. “Draw 0.4” is ambiguous at the syringe — 0.4 mL is 40 units, not 4. The calculator always returns the unit number so there is nothing to mistranslate.
• Forgetting the microgram-to-milligram step. A protocol quoted in mcg entered raw into a mg field is off by a factor of 1,000. Convert first (250 mcg = 0.25 mg).
• Assuming one water volume fits every vial. A concentration that reads cleanly on a 10 mg vial can produce an unreadable fractional unit on a 6 mg vial. Recompute whenever the vial or water changes.
• Overfilling a small vial. Planning more water than the glass holds is a physical impossibility the numbers won’t warn you about until you’re at the bench — check the vial capacity first.
• Mental-math rounding drift. Doing three conversions in your head invites small errors that compound. One deterministic calculation avoids it.

What retatrutide is studied for

Retatrutide is a triple agonist — it acts on the GLP-1, GIP, and glucagon receptors simultaneously — and is the newest entrant in the incretin class. It has been studied primarily for weight loss, and a Phase-2 trial reported roughly a 24% mean body-weight reduction at the highest dose, currently among the largest figures reported in the class. That headline is genuinely notable, but it deserves an honest asterisk: retatrutide’s long-term and safety dataset is smaller than what exists for semaglutide or tirzepatide, both of which have far more accumulated trial and real-world follow-up. It is administered once weekly by subcutaneous injection and is titrated upward over time. None of that is a recommendation — it is context for why the compound is discussed, framed around what the research has actually measured rather than what it promises.

Put it together

Enter your real vial size, your water volume, and your target dose above, and the calculator returns concentration, draw volume, units, and doses per vial in one step — the same four formulas shown here, applied without arithmetic risk. Before you reconstitute, walk through the full procedure in the peptide reconstitution guide, and check documented titration specifics on the retatrutide protocol page. If you want to sanity-check a number or ask how a different water volume changes your units, the OpenPeptide assistant can run the math with you.