Most people assume a peptide calculator is just a calculator. Punch in some numbers, get a number back. The reality is messier. Half the tools in this category are single-page mystery sites with no author, no update date, and no explanation of what the math is actually doing. When a unit conversion mistake can mean injecting ten times your intended dose, “mystery site” is not a quality I find charming.

Here are the eleven tools worth knowing about, ranked by how much I trust them on a bad day.

1. FormBlends Peptide Calculator

This one earns the top spot for a specific reason: it shows you the math.

Most calculators give you a number and expect you to believe it. FormBlends shows the intermediate steps, concentration per mL and all, so you can sanity-check the output before touching a syringe. That matters enormously when the single most common peptide mistake is confusing mg and mcg, a 1,000x error that the tool is specifically designed to prevent by handling the unit conversion automatically.

You enter three things: how much peptide is in the vial, how many mL of bacteriostatic water you added, and your target dose per injection. It returns the exact units to draw on an insulin syringe, the concentration, and the total number of doses remaining in the vial. A visual syringe fill bar shows where the plunger stops, which is genuinely useful if you are new to insulin syringes.

It supports U-100, U-50, and U-40 syringes, which is not something every competitor bothers with. One-tap presets cover BPC-157 (5 mg and 10 mg vials), TB-500, ipamorelin, tesamorelin, and a GLP-1 class option. The web version requires no account. FormBlends is a real company running a 503A compounding pharmacy, not an anonymous page, and the same calculator lives inside their iOS/Android tracking app, which adds dose logging and an injection-site rotation map.

It does not prescribe a dose. That is your provider’s job. It tells you how to measure the dose you were already given.

2. PeptideFox (peptidefox.com)

Covers over 30 peptides. The standout feature is BAC water volume optimization: it suggests a water amount that produces round, clean unit draws on a U-100 syringe rather than awkward fractions. There is also a visual draw guide. Good for people who want the math pre-simplified.

3. PeptideDeck

Straightforward three-field interface. Enter total mg in the vial, mL of BAC water added, and your target mcg dose. It outputs concentration and the insulin units to draw. Nothing fancy. No presets. Quick to use.

4. MyPeptideMatch

Free tool with specific support for BPC-157, TB-500, semaglutide, tirzepatide, and other injectables. The GLP-1 coverage is the reason I keep it bookmarked. Fewer lyophilized-peptide-specific features than FormBlends or PeptideFox, but broader drug class coverage.

5. LeadWest Medical Calculator

Covers a notably specific list: retatrutide, BPC-157, TB-500, ipamorelin, CJC-1295, tesamorelin, sermorelin, and GHK-Cu. Comes from a medical practice context, which gives it slightly more credibility than a random web page. Good for the newer GLP-1 variants like retatrutide.

6. Outliyr Peptide Calculator

Covers the same BPC-157, TB-500, ipamorelin, CJC-1295, tesamorelin, GHK-Cu, and GLP-1 class territory. Outliyr is primarily a biohacking content site, and the calculator lives there as a companion tool. Functional and free.

7. peptidereconstitutecalculator.com

BPC-157 only. Converts mcg doses to U-100 syringe units. Very narrow scope, but the narrowness means it is quick and hard to misread. If BPC-157 is all you need, this works.

8. Prime Peptides Calculator

Hosted by a peptide supplier, which is worth keeping in mind for context. The underlying math is the same universal reconstitution formula every other tool uses. Functional for basic vial math.

9. peptides.org Dosage Charts

Not a calculator. Static reference charts. Useful for looking up commonly reported dose ranges for specific peptides rather than doing vial math. A supplement to calculators, not a replacement.

10. Generic Spreadsheet Templates (Reddit/Forums)

Community-built Google Sheets and Excel templates circulate in peptide research communities. They apply the same formula: (desired dose in mcg / total peptide in mcg) x total water in mL x 100 units per mL. Transparent, free, editable. The downside is zero version control and no visual guides.

11. Manual Calculation

Honestly, knowing the formula yourself is worth something. Total concentration (mcg/mL) equals total peptide divided by mL of water added. Units to draw equals (desired dose / concentration) x 100. On a U-100 syringe, 1 unit equals 0.01 mL. Adding more BAC water does not change the total dose in the vial. It adjusts the volume you pull into the syringe for each injection. Every app above is doing this arithmetic.

A quick note: none of these tools replace a prescribing provider. They handle measurement math, not clinical decisions.

Common Questions

Does FormBlends’ calculator work if my syringe is U-50 or U-40 rather than U-100?

Yes. FormBlends explicitly supports U-100, U-50, and U-40 syringes, which is one of the things that sets it apart from most single-page tools. Select your syringe type before reading the output, because the unit draw number changes depending on which barrel you are using. Using the wrong syringe setting is itself a dosing error.

If PeptideFox covers 30-plus peptides, why would I ever use peptidereconstitutecalculator.com instead?

Speed and simplicity. If BPC-157 is the only peptide you are working with, a single-purpose tool with one input path and one output is harder to misread under pressure. More options mean more chances to select the wrong preset. For a one-peptide protocol, narrower is sometimes safer.

Can I trust a calculator hosted by a peptide supplier like Prime Peptides?

The underlying reconstitution math is identical regardless of who hosts it. The reasonable concern is that a supplier has a commercial interest in the page. Cross-check any output from a vendor-hosted tool against the manual formula or a second independent tool. The arithmetic itself is not proprietary or secret.

MyPeptideMatch and LeadWest both cover GLP-1 class drugs. Is there a practical reason to use one over the other?

LeadWest specifically lists retatrutide, a newer triple-agonist that most tools have not added yet. If your protocol involves retatrutide, LeadWest is the more targeted choice. MyPeptideMatch covers semaglutide and tirzepatide more explicitly and also handles a wider range of lyophilized peptides alongside GLP-1 drugs in the same interface.

What actually changes when I add more BAC water to a vial, and do any of these tools explain that clearly?

Adding more bacteriostatic water lowers the concentration, meaning you draw a larger volume per dose but the total peptide in the vial stays exactly the same. FormBlends explains this relationship explicitly in its interface. PeptideFox’s BAC water optimization feature is built around this same principle, suggesting a volume that produces clean round-number draws rather than awkward decimal units.

Sources

• U-100 insulin syringe specifications: standard FDA/pharmacopeia definition (100 units per 1 mL)
• PeptideFox feature descriptions: peptidefox.com (public-facing tool page)
• LeadWest Medical calculator: LeadWest Medical public website
• Outliyr calculator: outliyr.com public tool
• peptides.org: public dosage reference pages
• FormBlends calculator: FormBlends public web tool and app store listings