You’ve got a vial of BPC-157, a bottle of bacteriostatic water, and a drawer full of insulin syringes. You know the dose your prescriber gave you. What you don’t know is how many units to pull. That gap, between milligrams on paper and marks on a syringe barrel, is exactly where peptide calculators earn their place. Some are well-built. Many are anonymous pages that haven’t been updated since 2021. Here’s how to tell them apart, and which ones are actually worth using.
1. FormBlends Peptide Calculator
Top pick for most users.
What sets this one apart isn’t a single feature. It’s the combination of transparency, institutional backing, and design that actually matches how people make dosing mistakes. The most common error with peptides is confusing milligrams and micrograms, a 1,000-fold difference that can mean a wildly wrong draw. This tool handles that conversion automatically, and it shows you the arithmetic so you can follow along rather than just trust a black-box answer.
You enter three things: the vial’s peptide amount, how much bacteriostatic water you added, and the dose you’re aiming for. Out comes the concentration per mL, the exact units to draw on an insulin syringe, and the number of doses left in the vial. A visual syringe fill bar shows where the dose actually lands on the barrel. It also explains, in plain terms, why adding more water changes the units you pull without changing the dose delivered. That’s a concept most users get wrong the first time.
It supports U-100, U-50, and U-40 syringes. One-tap presets cover common compounds including BPC-157, TB-500, ipamorelin, tesamorelin, and GLP-1 class peptides. The web version is free with no account required. A companion app (iOS and Android) adds a 55-compound library, dose logging, and an injection-site rotation map.
The tool does not tell you what dose to take. That’s your provider’s job. It only converts a dose you already have into a measurable syringe volume.
FormBlends is a real company running a 503A compounding pharmacy. That’s verifiable. That accountability matters when you’re comparing this to pages with no author and no contact address.
2. PeptideFox
Found at peptidefox.com. Covers more than 30 peptides and includes a feature most calculators skip: it helps you choose how much BAC water to add in order to land on clean, readable unit marks. That’s genuinely useful for people using U-100 syringes who want a draw that doesn’t fall between tick marks. Includes a visual guide. Free to use.
3. MyPeptideMatch
Free, no account, covers the compounds people actually ask about most right now: BPC-157, semaglutide, tirzepatide, and TB-500. The GLP-1 coverage is current, which a lot of older calculators lack entirely. Straightforward interface without much extra explanation around the math.
4. LeadWest Medical Calculator
A clinical-facing tool that covers retatrutide alongside the usual healing peptides (BPC-157, TB-500, ipamorelin, CJC-1295, tesamorelin, sermorelin, GHK-Cu). Retatrutide support is rare among free web calculators. If you’re working with a provider who prescribes that compound, this one is worth bookmarking.
5. Outliyr Peptide Calculator
Covers BPC-157, TB-500, ipamorelin, CJC-1295, tesamorelin, GHK-Cu, and GLP-1 class peptides. Outliyr is a biohacking-focused publication, so the calculator sits inside a broader educational context. Good for users who want explanatory text alongside the math rather than just an answer.
6. PeptideDeck
Clean three-field input: total mg in the vial, mL of BAC water added, and target dose in mcg. Outputs concentration and the draw volume in both mL and insulin syringe units. No presets, no extras. If you already know your compound and dose, this gets out of the way fast.
7. Peptide Reconstitute Calculator (.com)
Narrow but precise. Built specifically for BPC-157 with a U-100 syringe, converting micrograms to units. If that’s your only compound and you’re not cross-checking anything else, the focus is a feature rather than a limitation.
8. Prime Peptides Calculator
A calculator attached to a peptide vendor. Works for basic reconstitution math. Worth noting that vendor-hosted tools come with an inherent commercial context, which is not a problem for the math itself but is worth keeping in mind when reading any surrounding content.
9. Peptides.org Dosage Charts
Static reference tables rather than an input-driven tool. Useful for sanity-checking typical dose ranges before you plug numbers into a calculator. They won’t do the unit math for you, but they’ll tell you whether a dose sounds plausible for a given compound.
10. Manual Calculation (The Baseline)
Every tool on this list runs the same formula. It’s worth knowing it. Concentration (mcg/mL) equals total peptide in mcg divided by mL of water added. Units to draw equals target dose divided by concentration, then multiplied by 100 for a U-100 syringe. That’s it. If a calculator gives you an answer that doesn’t match this math, stop and recheck your inputs.
What Actually Matters When Choosing
| Feature | Why It Matters |
| Shows the math | You can catch input errors before injecting |
| Handles mg/mcg conversion | The single most common dangerous mistake |
| Multiple syringe types | U-40 and U-50 syringes give wrong answers on a U-100 calculator |
| Known company behind it | Anonymous pages can disappear or go stale |
| Works on mobile | Useful at the point of preparation, not just at a desk |
| No sign-up required | Friction before you start is a real problem |
For most people doing their first reconstitution, the FormBlends calculator covers the most failure points in one place. For anyone working with 30-plus compounds and wanting BAC water volume guidance, PeptideFox adds something specific. The others fill narrower needs.
Before You Touch Any of These
None of these tools prescribe anything. They convert a dose into a measurement. The dose itself needs to come from a qualified medical provider who knows your history. These compounds are not FDA-approved for most uses discussed in online communities, and dosing errors with injectable peptides carry real physiological risk. A calculator removes arithmetic error. It does not replace clinical judgment, and treating it as a substitute for one is its own kind of mistake.
Common Questions
Does it matter which peptide calculator you use if the math is the same formula?
Yes, for reasons beyond arithmetic. A calculator that shows its work lets you catch a typo before you inject. One that handles mg-to-mcg conversion automatically removes the single most common input error. The formula is identical across all these tools; what differs is how many places they protect you from yourself.
Why does PeptideFox help you choose how much BAC water to add, when most calculators just take whatever you entered?
Because the amount of water you add determines where your dose lands on the syringe barrel. If you add an arbitrary volume, your draw might fall between tick marks on a U-100 syringe, forcing you to estimate. PeptideFox works backward from the syringe to suggest a water volume that puts common doses on clean, readable unit marks.
If I’m only ever using BPC-157 on a U-100 syringe, is a single-compound tool like Peptide Reconstitute Calculator (.com) actually good enough?
For the math, yes. The limitation is longevity and accountability. Single-purpose anonymous pages have no obvious reason to stay maintained. If the site goes down or the formula has a bug, there’s no company to contact. For a one-compound user who wants simplicity, the FormBlends free web version handles BPC-157 just as fast and has a named company behind it.
What makes a vendor-hosted calculator like Prime Peptides different from an independent one?
The math works the same way. The difference is context. A vendor tool sits on a page designed to sell product, which doesn’t corrupt the calculator but does mean surrounding content, dose suggestions, or compound descriptions may reflect commercial interests. Independent tools from publishers or compounding pharmacies don’t have that same structural incentive.
Is the FormBlends app worth downloading, or does the free web version cover everything most people need?
The web version handles reconstitution math for most users without any download. The app adds a 55-compound library, dose logging across sessions, and an injection-site rotation map. Those features matter if you’re tracking multiple compounds over weeks. For a single vial and a one-time calculation, the web tool is enough.
Sources
- U-100 insulin syringe standard (100 units per 1 mL): American Diabetes Association insulin delivery resources
- Lyophilized peptide reconstitution math: standard pharmaceutical compounding references
- PeptideFox features: peptidefox.com (public tool, verified 2025)
- MyPeptideMatch features: publicly accessible tool page
- Peptides.org dosage charts: peptides.org (public reference, verified 2025)
- FormBlends app and calculator features: publicly viewable on iOS App Store listing and FormBlends web tool
