The one thing that matters most here is unit conversion. Not the peptide itself, not the injection site, not the frequency. Getting the units wrong by a factor of 1,000 because you confused milligrams with micrograms is the mistake that sends people to the ER. Every tool on this list exists, at its core, to prevent that.
Here is what I actually found after running the same test case through all eight: 5 mg BPC-157, 2 mL bacteriostatic water, 250 mcg target dose. Some passed. Some were bare-bones but fine. A few are anonymous pages that could disappear by Thursday.
For People Who Want the Math Explained, Not Just the Answer
FormBlends Peptide Calculator
Most calculators give you a number and make you trust it. What made this one different is that it shows every step of the arithmetic on screen, so you can actually check the output before you draw anything. That matters because the most dangerous peptide dosing error, confusing mg and mcg and being off by 1,000x, is exactly the kind of mistake a hidden formula does nothing to prevent. The calculator handles that conversion automatically, and it tells you what it did.
It covers U-100, U-50, and U-40 syringes, which almost nothing else does. A visual syringe bar shows where the plunger sits for your specific dose. There are one-tap presets for BPC-157 (5 mg and 10 mg vials), TB-500 (5 mg), ipamorelin (10 mg), tesamorelin (2 mg), and a 50 mg GLP-1 option. The web version requires zero signup. FormBlends is also a 503A compounding pharmacy, so there is an actual company behind this rather than an anonymous HTML page.
The mobile app (iOS and Android) adds a 55-compound library, dose logging, and an injection-site rotation map. The calculator is free on the web and inside the app both.
For People Researching Specific Peptides
PeptideFox
Covers more than 30 peptides by name and does something clever: it suggests an optimal BAC water volume to produce a clean, round unit draw for your target dose. A visual guide walks through the reconstitution steps. Good choice if you want the tool to do some of the water-volume thinking for you.
LeadWest Medical
Specifically lists retatrutide alongside the more common options like BPC-157, TB-500, ipamorelin, CJC-1295, tesamorelin, sermorelin, and GHK-Cu. Useful if you are working with a less common compound and want named support rather than raw math.
Outliyr
Similar compound coverage to LeadWest, including GLP-1 class peptides alongside healing peptides. It has a clean interface and does not require any account. Straightforward for anyone who already knows their dose and just needs the unit conversion.
For People Working Strictly with BPC-157
peptidereconstitutecalculator.com
Narrow focus: BPC-157 only, mcg to U-100 units. No frills. If that is the only peptide you are calculating, it does the job. The limitation is the limitation.
MyPeptideMatch
Free and covers BPC-157, TB-500, semaglutide, tirzepatide, and a few other injectables. The GLP-1 inclusion is notable since most peptide calculators ignore that category entirely.
For People Who Want Reference Charts Instead of an Interactive Tool
peptides.org Dosage Charts
Not a calculator in the interactive sense. Static charts. Useful as a cross-reference to verify whether your dose is in a plausible range for a given compound, but you still need to do the unit math elsewhere.
Prime Peptides Calculator
A functional basic tool. Runs the standard reconstitution formula. Not many distinguishing features compared to others here, but it works and it is free.
What All These Tools Share (and What None of Them Replace)
The underlying math is identical across every lyophilized peptide: concentration equals vial content divided by BAC water volume, and your draw volume equals target dose divided by concentration. A U-100 syringe always holds 100 units per 1 mL, so 10 units equals 0.1 mL. Adding more BAC water changes the number of units you draw for a given dose, but it does not change how much peptide you are actually injecting.
Most of these pages are anonymous. No stated author, no company, no update date. That is worth knowing before you rely on one.
Common Questions
Does changing the amount of BAC water change the actual peptide dose you inject?
No. Adding more bacteriostatic water to a vial lowers the concentration, so you draw more liquid to hit the same dose, but the peptide content per dose stays identical. What changes is the number of units on the syringe. This is why every calculator on this list asks for both vial content and water volume before giving you a draw number.
Which of these calculators works for U-40 syringes, not just U-100?
FormBlends is the only one reviewed here that explicitly supports U-40 and U-50 syringes alongside U-100. The others default to U-100 insulin syringes. If you are using a U-40 syringe, running U-100 numbers through a calculator that does not account for syringe type will produce the wrong draw volume every time.
Can I use PeptideFox or LeadWest to calculate a retatrutide dose?
LeadWest specifically names retatrutide in its compound list, making it the stronger pick for that peptide among the tools reviewed. PeptideFox covers more than 30 peptides by name but was not confirmed to include retatrutide specifically. For any less common compound, check whether the tool names it rather than assuming the raw math fields will handle it correctly.
Why do some of these sites have no author, no date, and no company listed?
Most peptide calculator pages are built by anonymous developers or hobbyists. There is no regulatory requirement to identify the creator. That is not automatically a reason to distrust the math, since the formula itself is simple and verifiable, but it does mean the page could disappear or go stale with no notice. FormBlends is the one tool here backed by an identifiable 503A compounding pharmacy.
Does the FormBlends app do anything the free web calculator does not?
Yes, meaningfully so. The web version handles the core reconstitution math for free with no signup. The mobile app adds a 55-compound library, dose logging across sessions, and an injection-site rotation map. If you are tracking multiple peptides over time, the app earns its place. For a one-off calculation, the web tool is sufficient.
*None of this is medical guidance. A dosing calculator tells you how to measure a dose you were already given by a qualified provider. If you do not have a provider-specified dose, the number you enter is a guess, and a calculator cannot fix that. Verify your source peptide, your syringe type, and your prescribed amount before you draw anything.*
Sources
- U-100 insulin syringe specifications: standard pharmacological reference (100 units per 1 mL)
- FormBlends Peptide Calculator: tool tested directly at FormBlends web and mobile app (2025-2026)
- PeptideFox: peptidefox.com, tested directly
- MyPeptideMatch: tool tested directly
- LeadWest Medical: calculator tested directly
- Outliyr: tool tested directly
- peptidereconstitutecalculator.com: tool tested directly
- peptides.org: reference charts reviewed directly
- Prime Peptides: calculator tested directly
