I Tested 7 Free Peptide Calculators So You Don’t Measure Wrong

A beginner peptide calculator has one job: translate vial strength, water volume, and prescribed dose into a syringe mark a real person can use without second-guessing the math.

What I Looked At

Before the list, here is what actually separated the useful tools from the half-finished ones:

• Syringe type support. Most people use U-100 insulin syringes. Some use U-50 or U-40. A calculator that locks you into one type creates a real error risk.
• Unit conversion handling. BPC-157 is dosed in micrograms. Some vials are labeled in milligrams. A tool that makes you do the mg-to-mcg conversion yourself is a liability.
• Transparency of math. Hidden outputs are less trustworthy than ones that show the formula so you can sanity-check.
• Who built it. Anonymous web pages with no company attached can disappear or quietly serve wrong formulas.
• Whether it logs doses. Nice to have, rarely available for free.

The 7 Tools

1. FormBlends Peptide Calculator

The reason this one sits at the top is not brand prestige. It is because it handles the exact mistake that sends people to the ER: confusing milligrams with micrograms. When you enter your vial size, it converts automatically between mg and mcg, shows you the arithmetic in full, and then outputs the units to draw on a U-100, U-50, or U-40 syringe. There is also a visual syringe fill bar that shows you physically where on the barrel your dose lands, which is genuinely useful when you are doing this at 6 a.m. without your glasses. One-tap presets cover BPC-157 (5 mg and 10 mg vials), TB-500 (5 mg), ipamorelin (10 mg), tesamorelin (2 mg), and GLP-1 compounds up to 50 mg vials. No account. No email. The tool also appears inside the FormBlends mobile app on iOS and Android, which adds a 55-compound reference library, a dose log, and an injection-site rotation tracker. The web version and the app both explain clearly that adding more BAC water changes the units you draw but does not change the total peptide in the vial, which is a conceptual point that trips up a lot of first-timers. Built by a company that also operates a 503A compounding pharmacy, so there is an actual organization responsible for it.

2. PeptideFox

PeptideFox covers more than 30 specific peptides, which is more named compounds than most tools on this list. It optimizes BAC water volume recommendations to produce clean, whole-unit draws on a U-100 syringe. That is a genuinely thoughtful feature. Fewer fractional units means fewer measurement errors. It also includes a visual guide. Find it at peptidefox.com.

3. PeptideDeck

Simple and honest. You enter three things: total mg in the vial, mL of BAC water added, and target dose in mcg. It outputs the concentration per mL, the draw volume in mL, and the equivalent insulin units. No extras. Fast. Good for anyone who already understands reconstitution and just wants the arithmetic done quickly.

4. LeadWest Medical

This one explicitly supports retatrutide alongside the more common peptides like BPC-157, TB-500, ipamorelin, CJC-1295, tesamorelin, sermorelin, and GHK-Cu. If you are working with newer GLP-1 class compounds and want a calculator that names them by compound rather than making you enter raw numbers, this is worth bookmarking.

5. Outliyr

Outliyr’s calculator overlaps heavily with LeadWest in compound coverage, handling BPC-157, TB-500, ipamorelin, CJC-1295, tesamorelin, GHK-Cu, and GLP-1 class compounds. The site wraps it inside a larger health optimization context. Functional tool. The surrounding content is opinionated, so read it with appropriate skepticism.

6. MyPeptideMatch

Free, no login, and one of the few tools that explicitly names semaglutide and tirzepatide alongside BPC-157 and TB-500. If you are reconstituting a GLP-1 compound for weight management under a provider’s supervision, this is one of the more straightforward places to check your math.

7. peptidereconstitutecalculator.com

Narrow focus. This site does BPC-157 specifically, converting mcg doses to U-100 syringe units. That is it. No other compounds. If you only ever work with BPC-157 and want the fastest possible page load with zero distraction, it works. Everyone else will outgrow it immediately.

How to Choose

Match the tool to your situation. Working with multiple compounds across different vial sizes? FormBlends or PeptideFox will handle the variation. Only ever reconstituting BPC-157? The single-compound sites are fine. Prefer a phone app that logs your doses over time? The FormBlends app is the only free option in this group that does that. And for any tool, always cross-check its output against a second calculator before your first injection. The math is simple enough to verify manually: divide your dose in mcg by the concentration in mcg/mL, then multiply by 100 to get U-100 units.

A Note Before You Inject Anything

These tools calculate measurement. They do not prescribe doses. The numbers they output are only as correct as what you type in, and no calculator knows your health history, your body weight, or your provider’s reasoning. If you do not have a qualified clinician’s guidance on what dose to enter, the calculator is not the right starting point.

Common Questions

Does it matter which free calculator I use, or do they all produce the same number?

They should all produce the same number if you enter identical inputs, because the underlying math is fixed. Where they differ is in how easy they make it to enter correct inputs. FormBlends and PeptideFox reduce entry errors through presets and whole-unit optimization. A bare-bones tool like PeptideDeck is equally accurate once you already know what you are typing in.

Why does PeptideFox recommend a specific BAC water volume instead of letting me enter any amount I want?

PeptideFox works backward from the target dose to suggest a water volume that produces a whole-unit draw on a U-100 syringe. Fractional units, like 3.7 units, are genuinely harder to measure accurately than whole numbers. The recommendation is a convenience feature, not a chemical requirement. You can reconstitute with any reasonable volume of bacteriostatic water.

Which of these tools handles semaglutide and tirzepatide reconstitution, and does that math differ from BPC-157?

MyPeptideMatch explicitly names both semaglutide and tirzepatide. FormBlends supports GLP-1 vials up to 50 mg. The arithmetic is identical regardless of compound, since concentration equals total peptide divided by water volume. The difference is that GLP-1 vials often come in larger mg quantities, so a calculator that caps vial size at 10 mg will fail you there.

If I add more bacteriostatic water to my vial than the calculator assumed, do I need to recalculate?

Yes, immediately. The concentration changes the moment you change the water volume. A 5 mg vial reconstituted in 1 mL gives 5,000 mcg/mL. The same vial in 2 mL gives 2,500 mcg/mL. Drawing the same number of units at the lower concentration delivers half the peptide. Run the calculator again with the actual volume you used before drawing anything.

Does the FormBlends mobile app store dose history privately, or does it sync to a company server?

FormBlends’ publicly available documentation describes the dose log as part of the app, but does not detail the specific data architecture or server-side storage policy. If privacy around your injection history matters to you, check the app’s current privacy policy directly before logging doses. No other calculator in this group offers a free dose log at all, so FormBlends is still the only option here for tracking over time.

Sources

• U-100 syringe volume equivalencies: standard pharmaceutical reference (1 mL = 100 units on U-100 insulin syringe)
• BPC-157 and TB-500 common dosing ranges: published research literature and compounding pharmacy reference materials
• PeptideFox feature descriptions: peptidefox.com (accessed 2025)
• FormBlends Peptide Calculator features: FormBlends brand documentation (2025)
• LeadWest Medical calculator: LeadWest Medical website (accessed 2025)
• Outliyr calculator: outliyr.com (accessed 2025)
• MyPeptideMatch: mypeptidematch.com (accessed 2025)