Using the OHM dosing calculator: worked examples for five common peptides

Short answer: using the OHM dosing calculator worked well enough for me that I now default new clients to it instead of a cheat-sheet screenshot, because the calculator does the mg-to-unit math live off your actual vial and water volume instead of a generic table that assumes everyone reconstituted the same way. I built this piece around three peptides people ask about constantly, BPC-157, semaglutide, and retatrutide, because the same three inputs (vial strength, water volume, target dose) trip people up in three different ways depending on the compound.

I've walked probably a hundred people through their first reconstitution over the phone, and the fear is never the injection itself. It's the arithmetic. A vial says 10 mg. The water vial says nothing useful at all. And somewhere in the middle you're supposed to land on "10 units" and trust that number with a needle in your hand. Below are the actual worked examples, the ones I'd want in front of me the first time.

How the calculator actually works, in three inputs

The calculator only needs three things: total peptide in the vial (mg), water added (mL), and the dose you're targeting (mcg or mg). From those it computes concentration (mg/mL), then converts your target dose into both mL and syringe units, assuming a standard U-100 insulin syringe where 100 units equals 1 mL.

The formula underneath, if you ever want to check it by hand:

Concentration = total mg ÷ mL of water. Dose volume = target dose ÷ concentration. Units = dose volume in mL × 100.

That's it. Every "worked example" below is just that formula run with a different vial.

Worked example one: BPC-157

BPC-157 is the most common first peptide people reconstitute, and the community-standard protocol that's converged around it, 250 to 500 mcg once or twice daily, is well supported by a genuinely deep animal literature on tendon and gut repair, even though the human trial base is still thin.

Say you bought a 10 mg vial and add 2 mL of bacteriostatic water.

Concentration = 10 mg ÷ 2 mL = 5 mg/mL, which is 5,000 mcg/mL.

If your target dose is 500 mcg: dose volume = 500 ÷ 5,000 = 0.1 mL. Units = 0.1 mL × 100 = 10 units.

If you want the lower end of the range, 250 mcg, that's half the volume: 0.05 mL, or 5 units. Simple to double-check on an insulin syringe because the marks are already in units, not mL.

The mechanistic case for BPC-157 rests heavily on the FAK-paxillin pathway that lets fibroblasts migrate into a wound and rebuild it, plus a downstream ERK1/2 route that governs collagen gene expression once those cells arrive. Animal work on Achilles tendon-to-bone repair and ligament healing is what the human dose is extrapolated from, which is exactly why getting the reconstitution math right matters more here than with an FDA-labeled drug: there's no package insert doing the arithmetic for you.

Worked example two: semaglutide

Semaglutide is a prescription drug, dispensed either as brand-name or through a compounding pharmacy, and it starts at a much lower per-injection amount than BPC-157. A common compounded vial is 15 mg reconstituted with 6 mL of bacteriostatic water.

Concentration = 15 mg ÷ 6 mL = 2.5 mg/mL, or 2,500 mcg/mL.

The standard starting dose is 0.25 mg (250 mcg) weekly. Dose volume = 250 ÷ 2,500 = 0.1 mL. Units = 10 units.

Step up to 0.5 mg: dose volume doubles to 0.2 mL, or 20 units. At the full obesity maintenance dose of 2.4 mg: dose volume = 2.4 ÷ 2.5 = 0.96 mL, or 96 units, just under a full syringe. Running this ladder through the calculator instead of memorizing it matters because vial concentration varies by pharmacy. A 20 mg vial in 4 mL, for instance, gives you 5 mg/mL, twice the concentration above, and every unit count above would be cut in half for the same dose.

Worked example three: retatrutide

Retatrutide is the newest and most powerful of the three, a triple agonist still in Phase 3 trials, sold as a research compound rather than an approved drug. A 10 mg vial reconstituted with 2 mL of bacteriostatic water is the standard reference point.

Concentration = 10 mg ÷ 2 mL = 5 mg/mL.

Most weight-loss users start at 2 mg weekly and never go higher than 8 mg without a specific reason, since the Phase 3 TRIUMPH data shows the marginal gain from 8 mg to 12 mg is small while the side-effect dropout rate roughly triples. At 2 mg: dose volume = 2 ÷ 5 = 0.4 mL, or 40 units. At 8 mg, the sweet-spot ceiling for most users: dose volume = 8 ÷ 5 = 1.6 mL, which is more than a single standard insulin syringe holds, so this is typically split across two injections or drawn with a 3 mL syringe.

This is where the calculator earns its keep. Doing that math by hand while also trying to remember whether you're supposed to round up or down is exactly how people end up injecting double their intended dose.

Where people actually make mistakes

The error I see most isn't a wrong formula, it's applying last month's unit count to this month's vial. You switch pharmacies, the new vial is 20 mg instead of 10 mg, you reconstitute with the same 2 mL out of habit, and now every unit on your syringe is worth twice as much peptide. Rerun the calculator any time the vial size, water volume, or peptide changes. Don't carry a number in your head from one bottle to the next.

The second common mistake is treating "units" as a universal currency across peptides. Ten units of BPC-157 at 5 mg/mL is 500 mcg. Ten units of semaglutide at 2.5 mg/mL is 250 mcg. Same syringe mark, different drug, different dose entirely.

Before you write any of this down, the obligatory version my lawyer insists on, and he's right to: The doses and schedules here are for educational and informational purposes only. These peptides are sold for research use only and are not FDA-approved drugs. This is not medical advice. Consult a qualified physician before beginning any protocol.

If you're new to reconstitution generally, Bacteriostatic vs Sterile Water: Which One, and Why covers the water side of this equation, and Auto-Injector Pens for Peptides is worth a look once you're running more than one compound and want to simplify the daily routine. For the peptides themselves, the full BPC-157, semaglutide, and retatrutide pages carry the mechanism and evidence detail this piece deliberately kept out of the way.

Run the numbers once, check them against the calculator, and you stop having to trust a stranger's forum screenshot for something you're about to inject.