Peptipedia

Peptide Injection Calculator

This free calculator helps you reconstitute (mix) a peptide correctly and find the right draw amount for your U100 insulin syringe - concentration, marks (IU), millilitres to draw and doses per vial. Pick the peptide, vial size and your desired dose; it computes the rest live and suggests a suitable amount of BAC water. The full procedure is in the step-by-step reconstitution guide. A calculation aid only, no sign-up - nothing is stored.

Note: a calculation aid only, not medical advice and not a dosing recommendation. When in doubt, consult a physician.

Work clean: disinfect the rubber stopper with an alcohol swab, use a new sterile needle, and check the solution. Full procedure in the Guide.

Calculation aid, not a dosing recommendation.

Free registered users also get the Injection Manager: it stores the mixes and reconstitutions you create, calculates the doses from them, lets you log your injections and tracks along. You always keep the full picture!

How does the peptide injection calculator work?

The calculator takes three values - the vial size in milligrams of powder, the amount of bacteriostatic water you add in millilitres, and your desired dose - and works out the concentration, the amount to draw, the marks (units, IU) on the insulin syringe, and the number of injections per vial. So you don't have to do the maths yourself.

Reconstituting means mixing the freeze-dried peptide powder in the vial with bacteriostatic water into a ready injection solution. The calculator steps in exactly here: it turns the abstract milligrams on the label into the concrete number you later read off the syringe. It also suggests a water amount that puts your dose on marks that are easy to read.

How much bacteriostatic water should I use?

The water amount alone decides how finely you can read your dose - it does not change the amount of active ingredient in the vial. More water lowers the concentration (mg per ml), so one dose is spread over more marks and is easier to read. Less water concentrates the solution and you draw less.

Concentration is simply mg of powder divided by ml of water. The calculator's suggestion aims to land your dose on a round, comfortably readable number of marks, so you don't misjudge when drawing. As a comfort note: smaller injection volumes are usually felt as more pleasant subcutaneously.

How do I convert the dose into marks on the insulin syringe?

On a U100 insulin syringe, 100 units (IU) equal exactly 1 ml, so a single mark is 0.01 ml. The units to draw come from your desired dose divided by the amount of active ingredient per mark, which in turn depends on the concentration. The calculator does this conversion automatically.

Almost all common insulin syringes are U100; the packaging says "U-100" or "100 IU/ml". Check that briefly, because rare U-40 syringes carry a different scale and would distort the reading. Go by the syringe's unit scale, not by millilitre markings of other syringe types.

What if I would need to draw more than 1 ml?

If the calculated amount is clearly above roughly 1 ml, that is often a sign the solution is mixed very thin for your dose - then it's worth looking at a more concentrated mix with less water. Up to about 1 ml most people find a subcutaneous injection unproblematic.

From around 1.5 ml some report a more uncomfortable feeling and then split the volume across two injection sites. That is purely an experience and comfort note, not a medical rule. The calculator helps you pick a water amount up front that keeps you in a volume range that is comfortable for you.

Frequently asked questions

What is a peptide calculator?

A peptide calculator works out the exact liquid volume you need to draw up to inject a given dose. Because peptides ship as a freeze-dried powder (the technical term is lyophilisate), you first mix them with bacteriostatic water (BAC - a sterile water with a preservative that stops bacteria from growing, keeping it usable for several withdrawals). The calculator removes the guesswork from converting milligrams of powder into millilitres on the syringe.

Why is the calculation so important?

Peptides are highly potent - meaning they work extremely strongly even in the tiniest amounts. Because even the smallest measuring error with the liquid leads to a large over- or underdose, a wrong dose can reduce effectiveness or cause side effects. The calculation matters because tiny volume differences translate into large dose differences. The calculator removes the risk of human arithmetic errors and ensures you get the exact right dose every time.

What is BAC water?

BAC stands for 'bacteriostatic water' - literally 'bacteria-inhibiting water'. It contains about 0.9% benzyl alcohol (the preservative that does the bacteria-inhibiting job), which stops bacteria from multiplying in an opened vial (small glass bottle). You need it to dissolve freeze-dried peptide powder in the vial so you can inject it over several days. It matters because it lets you store a vial of dissolved peptide in the fridge and draw from it several times without bacteria growing in it. Never use tap water or boiled water for injections.

How do I calculate the right peptide dose?

The peptide comes as a powder in the vial. You add a measured amount of water to dissolve it, then draw up only part of that liquid, exactly the part that contains your target dose. Here's how to calculate that part:

Volume to draw up (ml) = (target dose ÷ vial strength) × BAC water (bacteriostatic water, sterile water used to dissolve the powder) added. Example: 250 mcg target (1 mg = 1,000 mcg), 5 mg (5,000 mcg) vial, 2 ml water → (250 ÷ 5,000) × 2 = 0.1 ml. On a U100 insulin syringe (where 1 ml = 100 units), 0.1 ml = 10 units (IU, International Units). This formula always converts your target dose into a volume you can read on the syringe.

Units (IU) or ml - what counts on the syringe (U-100, U-40, 50-unit syringe)?

What matters is the syringe's scale (U-100 or U-40), not its size. On the common U-100 insulin syringe: 100 units (IU) = 1 ml. So 50 IU = 0.5 ml, 20 IU = 0.2 ml, 10 IU = 0.1 ml.

Don't confuse the scale with the barrel size: U-100 syringes come in different capacities. The most common for peptides is the "50-unit" (0.5 ml) - it holds at most 50 IU = 0.5 ml. A full millilitre does not fit; 1 ml equals 100 IU, i.e. a full 1-ml/100-unit syringe. Common U-100 sizes:

  • 0.3 ml = 30 IU (U-100)
  • 0.5 ml = 50 IU (U-100) - the most common
  • 1.0 ml = 100 IU (U-100)

Less common is the U-40 scale (40 IU = 1 ml, i.e. 10 IU = 0.25 ml), typical for some veterinary insulins. Always read the "U-100" or "U-40" marking on the syringe and convert accordingly. The injection calculator gives you the right volume.

How much BAC water should I use?

Choose a practical amount: not too little (dissolves poorly, stings) and not too much (the injection volume becomes too large). For standard vials (5-10 mg, the small peptide vials with a rubber stopper), 2-3 ml is a proven default. Use BAC water (bacteriostatic water - sterile water with a preservative, the standard diluent for peptides). In short: more water lowers the concentration, so you need to pull more liquid into the syringe for the same dose.

Can I change the concentration?

Yes. More water lowers the concentration, so you draw up a larger volume for the same dose; less water does the opposite. You don't have to calculate yourself: once you change the water volume in the calculator, it automatically adjusts the volume for you.

My vial has less BAC water than planned - how do I recalculate the dose correctly?
Think of cordial: add less water and each sip is stronger. That is exactly what happened when too little BAC water (bacteriostatic water - sterile water with a small amount of preservative that inhibits bacterial growth; the standard for mixing peptides) went into your vial - the peptide sits more concentrated, so every unit on your syringe now carries more active ingredient than planned. Peptides such as tirzepatide (a GLP-1/GIP peptide hormone - a lab-made hormone that mimics your body's natural GLP-1 and GIP signals for satiety and blood sugar) and other GLP-1 analogues (peptides with a similar mode of action) become more concentrated than planned when less BAC water is in the vial than intended. Every unit on the syringe then contains more mg of active ingredient than your calculator assumed. Here is what to do:
  1. Recalculate the concentration
    What you do: work out the actual concentration.
    Formula: concentration (mg/ml) = peptide in the vial (mg) ÷ water actually added (ml).
    Help: run it through the dose guide.
  2. Find the volume per dose
    What you do: figure out how many ml to draw up.
    Formula: volume per dose (ml) = desired dose (mg) ÷ actual concentration.
    Convert for the syringe: on a U-100 syringe (the standard insulin syringe - 100 units equal exactly 1 ml) multiply by 100 to get insulin units. Or use the shortcut: units (IU - International Units, the markings on the syringe) × 0.01 ml = ml per dose.
  3. Work out remaining doses
    Formula: remaining doses = leftover volume in vial ÷ volume per dose.
  4. Use up the vial, then start fresh
    What you do: finish the remaining vial, then mix a new one correctly.
Important hindsight: if you dosed by units based on the planned (lower) concentration, you actually drew up more mg per syringe than intended - that explains the stronger effect per dose. The vial running out early, on the other hand, came down to the total volume: there was simply less liquid in the vial. For the next vial, plan the water amount with the peptide calculator first: more water gives a larger, easier-to-read volume and reduces measurement error when drawing up.

Work it out: if your vial already came up short, the reverse dose calculator reconstructs how many mg you really had per injection.

What's the difference between research peptides and approved peptide drugs?

Short version: "Research peptides" are lab chemicals, not approved medicines. Anyone who sells them as "for research only" but simultaneously advertises healing, weight loss, or anti-aging is operating in a legal gray zone.

Research peptides (usually labeled 'Research Use Only', or RUO) are chemicals intended for in-vitro laboratory work (i.e., in test tubes, outside a living body) - not approved for human use and with no marketing authorization from any health authority. Approved peptide medicines such as semaglutide (Ozempic/Wegovy) or tirzepatide (Mounjaro/Zepbound), by contrast, have completed a full, multi-year regulatory review (in the US via official approval filings such as an NDA or BLA - NDA stands for New Drug Application for chemical drugs, BLA for Biologics License Application for biologics; in the EU via the EMA), are produced under cGMP (current Good Manufacturing Practice - strict, regulator-audited manufacturing standards), carry a reviewed label with the approved medical use (indication), dose, and warnings, and are dispensed by prescription through licensed pharmacies.

A useful everyday analogy: cGMP and regulatory approval work a bit like a vehicle inspection sticker - without it, the car may still drive, but it is not legally allowed on the road.

The key principle: under the FD&C Act (Section 201(g)), a product is legally a drug based on its claimed 'intended use' - which means an 'RUO' sticker does not protect a vendor who simultaneously markets weight loss, diabetes cure, or anti-aging benefits. The FDA has been closing this gap with warning letters to peptide shops.

  • Approved drug: reviewed indication, dose, and manufacturing - verifiable in the Drugs@FDA database and the current DailyMed label.
  • RUO research peptide: no reviewed indication, no reviewed dose, no reviewed manufacturing - 'RUO' is a vendor sticker, not an official status.
  • Compounded peptide (a peptide prepared individually by a pharmacy): a preparation made individually by a specially licensed US pharmacy (registered under FDA rule 503A) against an individual prescription; only lawful with bulk substances (the approved raw active ingredients) on the FDA list, otherwise still legally an "unapproved new drug" - meaning it is treated by regulators like an illegally marketed medicine.

Which peptides are actually approved and what risks the gray market carries, I summarize in the FAQ on peptide quality and gray-market risks.

What this means for you: Peptides sold as "research" but marketed with anti-aging, weight loss, or diabetes-cure claims are legally unapproved medicines - stay away. Approved peptide medicines are only available through a doctor's prescription and a licensed pharmacy.