Something shifted in the past year or so. Peptide calculators went from being rough Reddit-linked spreadsheets to actual products someone thought carefully about. That’s partly because GLP-1 compounds brought a wave of new users who had never touched a syringe before, and partly because the math errors that happen when you confuse milligrams with micrograms are genuinely dangerous. The space got more serious. Some tools deserve your trust. A lot still don’t.
Here’s what I actually use, what I’ve tested, and what I’d skip.
1. FormBlends Peptide Calculator
The one I come back to most. It’s a free web tool, no account required, and it solves the exact problem that trips up new users: you enter what’s in the vial, how much bacteriostatic water you added, and the dose you’re aiming for, and it tells you exactly which unit mark to draw to on your syringe.
What makes it worth recommending over the others is that it shows the underlying math. You can see how it got to 18 units. That matters when you’re second-guessing yourself at midnight with a $200 vial on the counter.
It also handles U-100, U-50, and U-40 syringes, which almost no other free tool does. Most assume U-100. If you’ve ever used a U-40 and been off by 2.5x, you know why that matters.
The mg-to-mcg conversion is automatic. Mixing those up by a factor of 1,000 is the single most common serious peptide dosing error, and the tool is clearly built around preventing it. One-tap presets cover BPC-157 (5mg and 10mg vials), TB-500, ipamorelin, tesamorelin, and GLP-1 compounds at 50mg. A visual fill bar shows where your dose sits on the syringe barrel. The same calculator lives inside the FormBlends mobile app, which adds dose logging and an injection-site rotation map.
FormBlends is an actual telehealth and pharmacy company, not a GitHub project someone abandoned. That’s not nothing.
2. PeptideFox
Covers more than 30 named peptides and is one of the cleaner interfaces I’ve used. Its standout feature is BAC water volume optimization. It suggests how much water to add based on your target dose and syringe type, so you get a clean unit draw instead of squinting at 7.3 units. The visual guide helps beginners orient to a real syringe.
3. PeptideDeck
Simple and honest about what it is. Enter your vial size in mg, the water you added in mL, and your target dose in mcg. It spits out the concentration and exactly how many units to pull. No presets, no extras. That simplicity is sometimes exactly what you want.
4. MyPeptideMatch
Free and covers a wider category mix than most: BPC-157, TB-500, semaglutide, tirzepatide, and other injectables. Good for someone managing multiple compounds who wants one tab open instead of four.
*Quick honest note: none of these tools prescribe anything. They’re measurement aids. Your provider sets the dose. These tools just tell you where the line is on the syringe.*
5. LeadWest Medical Calculator
Has the most specific peptide list I’ve seen from a medical-adjacent site. Retatrutide, BPC-157, TB-500, ipamorelin, CJC-1295, tesamorelin, sermorelin, GHK-Cu. If your compound is on that list, the output is clean and credible.
6. Outliyr Peptide Tool
Covers a solid overlap with LeadWest: BPC-157, TB-500, ipamorelin, CJC-1295, tesamorelin, GHK-Cu, plus GLP-1 class compounds. Good educational framing around the math. Slightly more text-heavy than some users want, but the explanations are genuinely useful for first-timers.
7. peptidereconstitutecalculator.com
Narrow scope, BPC-157 only, U-100 syringe only. But within that lane it’s clean and fast. If BPC-157 is all you’re working with, this gets the job done in ten seconds.
8. peptides.org Dosage Charts
Static reference tables, not a live calculation tool. Useful for sanity-checking a protocol you’ve already mapped out, less useful for doing live reconstitution math.
9. Prime Peptides Calculator
Basic reconstitution math, straightforward inputs and outputs. Works fine for common lyophilized peptides. Fewer features than the top options, but it’s accessible and loads quickly.
10. DIY Spreadsheet (Google Sheets or Excel)
Unglamorous but worth including. The reconstitution formula is fixed: (desired dose in mcg / total mcg in vial) multiplied by total mL of water, multiplied by 100 for U-100 units. Any spreadsheet can do this. You own the math, nothing breaks, and you can add your own compound names. The tradeoff is zero error-checking on unit confusion.
What I’d Tell a Friend
Start with the FormBlends tool. Show the math, check your units, confirm the syringe type before you draw. The fundamental reconstitution formula is the same for every lyophilized peptide, so any of these tools can technically work. The difference is whether you can verify what the tool is actually doing, and whether someone real built it or not.
Common Questions
Does the FormBlends calculator work if my syringe isn’t U-100?
Yes, and that’s genuinely rare among free tools. FormBlends explicitly supports U-100, U-50, and U-40 syringes. You select the type before calculating. Using the wrong syringe setting without that correction produces a 2.5x error on U-40, which is the kind of mistake that ruins an expensive vial.
What’s the actual math behind any mcg-to-units conversion, and can I check these calculators against it?
The formula is: (dose in mcg divided by total mcg in vial) multiplied by total water added in mL, multiplied by 100 for a U-100 syringe. Run that in a spreadsheet and compare it to whatever tool you’re using. FormBlends and PeptideDeck both show their work, so verification is straightforward.
PeptideFox suggests how much BAC water to add. Is that actually useful or just a gimmick?
It’s useful. The amount of water you add determines your concentration, which determines whether your dose lands on a clean unit mark or an awkward fraction. PeptideFox optimizes that starting point based on your target dose and syringe type, which reduces rounding guesswork and makes drawing more repeatable.
If I only use BPC-157, is there any reason to use something more complex than peptidereconstitutecalculator.com?
Not really, as long as you’re using a U-100 syringe. That tool is BPC-157 and U-100 only, and within those constraints it’s fast and accurate. The reason to step up to FormBlends or PeptideFox would be if you add a second compound, switch syringe types, or want the calculation explained rather than just stated.
Do any of these tools work for GLP-1 compounds like semaglutide or tirzepatide, or are they peptide-specific?
MyPeptideMatch covers semaglutide and tirzepatide directly. FormBlends includes GLP-1 compound presets at 50mg. Outliyr also covers GLP-1 class compounds. The underlying math is identical to other lyophilized peptides, but having the correct vial size preset matters because GLP-1 vials are typically much larger than BPC-157 or ipamorelin vials.
Sources
- U-100 insulin syringe standard (100 units per mL): FDA syringe labeling guidance, verified
- mg to mcg conversion (1 mg = 1,000 mcg): NIST unit reference
- PeptideFox features: peptidefox.com, reviewed January 2026
- PeptideDeck features: public tool, verified 2026
- MyPeptideMatch features: public tool, verified 2026
- LeadWest Medical calculator: leadwest.com, verified 2026
- Outliyr peptide calculator: outliyr.com, verified 2026
- peptidereconstitutecalculator.com: public tool, verified 2026
- peptides.org dosage charts: peptides.org, verified 2026
