The most common mistake I see people make with peptide dosing isn’t picking the wrong vial size or the wrong injection site. It’s the mg-vs-mcg confusion. Someone reads “0.5 mg” on their protocol, enters it as 500 into a calculator expecting mcg, and suddenly they’re calculating a dose that’s 1,000 times off. That’s not a rounding error. That’s a serious problem. Good tools catch it. Bad ones let it slide.
Here are the eight peptide dose calculators I actually looked at, ranked by how useful they are in practice.
1. FormBlends Peptide Calculator
Verdict: The most complete free tool I found, and the one I’d hand to a first-timer.
Most calculators give you a number. This one shows you the math behind it, which matters a lot when you’re learning. You enter three things: how many mg or mcg are in your vial, how much bacteriostatic water you added in mL, and your target dose per injection. Out comes the concentration per mL, the exact number of units to draw, and a visual bar showing where that dose sits on the syringe.
The mg-to-mcg auto-conversion is built in and explained. If you type 5 in the mg field, it doesn’t silently treat that as 5,000 mcg and let you move on. It handles the conversion and labels it clearly.
A few things set it apart from everything else on this list. First, it covers U-100, U-50, and U-40 syringes, not just the standard insulin syringe most calculators assume you’re using. Second, the one-tap presets for peptides like BPC-157, TB-500, ipamorelin, tesamorelin, and GLP-1 compounds save real time. Third, the same calculator lives inside the FormBlends mobile app (iOS and Android), which also includes a 55-compound reference library, dose logging, and an injection-site rotation tracker. That’s genuinely useful for anyone doing multi-peptide protocols over weeks.
FormBlends is an actual telehealth and 503A compounding pharmacy company, not an anonymous domain. The tool is free, requires no account, and makes clear it only tells you how to measure a dose your provider already gave you. It does not suggest what dose to take.
2. PeptideFox
Verdict: Strong visual presentation, good for 30-plus peptides.
PeptideFox at peptidefox.com covers more than 30 individual peptides and includes a visual guide alongside its output. One feature I appreciated: it optimizes the BAC water volume recommendation to give you clean unit draws on a standard insulin syringe, so you’re not trying to draw 37.8 units and squinting at a barrel. Practical thinking.
3. PeptideDeck
Verdict: Straightforward math, no extras, works fine.
Enter your vial’s mg, your BAC water in mL, and your target dose in mcg. PeptideDeck outputs concentration and the number of units to draw. That’s the whole loop. No presets, no visuals, no app. But the core calculation is there, and it’s clean.
4. MyPeptideMatch
Verdict: Free, covers GLP-1 compounds that most calculators ignore.
Free and no-login required. What makes it worth mentioning is the coverage: BPC-157, semaglutide, tirzepatide, TB-500, and other injectables. Most peptide calculators were built when GLP-1 compounds were barely on anyone’s radar. MyPeptideMatch includes them, which reflects where the space actually is right now.
5. LeadWest Medical
Verdict: Clinical framing, good peptide range, worth bookmarking.
LeadWest Medical’s calculator covers retatrutide, BPC-157, TB-500, ipamorelin, CJC-1295, tesamorelin, sermorelin, and GHK-Cu. The medical-company framing gives it a bit more context than a random page, though I’d still verify any output against your provider’s protocol. Retatrutide support is a differentiator.
6. Outliyr
Verdict: Biohacking-audience tool with solid peptide coverage.
Outliyr covers BPC-157, TB-500, ipamorelin, CJC-1295, tesamorelin, GHK-Cu, and the GLP-1 class. It’s aimed at the self-optimization crowd and is more editorial in tone than the pure-math tools. Good for someone who wants context alongside the conversion output.
7. peptidereconstitutecalculator.com
Verdict: BPC-157 only, but clean for that one use case.
This site does exactly one thing: BPC-157, mcg to units on a U-100 syringe. If that’s your only need, it’s fine. If you ever move to a different peptide or a different syringe, you’ll need something else. Narrow scope, decent execution.
8. peptides.org Dosage Charts
Verdict: Reference, not a calculator. Useful for context, not for drawing doses.
Peptides.org offers static dosage charts rather than an interactive tool. You won’t get a “draw X units” answer here. What you will get is a reasonably well-organized reference for typical dosing ranges across a range of compounds. I use it as background reading, not as the thing I consult while holding a syringe.
One Thing Every Tool Gets Right (and Why It Matters)
The math behind reconstituting any lyophilized peptide is the same regardless of what the peptide actually is. Add more water, and you draw more units to get the same dose. Add less water, and you draw fewer. The total dose doesn’t change. Every calculator here reflects that correctly, even if they differ in how clearly they explain it.
A U-100 insulin syringe holds 100 units per 1 mL. That’s fixed. What changes between protocols is concentration, and concentration changes every time someone reconstitutes a vial with a different water volume. Any tool that doesn’t account for variable water volume is incomplete.
Common Questions
Does it matter which syringe type I tell the calculator I’m using?
Yes, and it matters more than most people expect. A U-40 syringe and a U-100 syringe will show completely different unit markings for the same physical volume of liquid. FormBlends explicitly supports U-40, U-50, and U-100 options. Most other tools on this list assume U-100 only, so entering the wrong syringe type produces a wrong draw every time.
If I change how much BAC water I add to a vial, do I need to recalculate everything?
Every single time, yes. The peptide dose stays the same, but the concentration changes with every different water volume. Add 2 mL instead of 1 mL and your units-to-draw figure doubles. PeptideDeck, FormBlends, and PeptideFox all take BAC water volume as a direct input precisely because this variable is the one people most often get wrong after the first reconstitution.
Which calculators on this list actually handle semaglutide and tirzepatide, not just research peptides?
MyPeptideMatch and Outliyr both cover GLP-1 compounds including semaglutide and tirzepatide. FormBlends lists GLP-1 compounds among its presets as well. LeadWest Medical includes retatrutide, which is notable since that compound appears on very few other tools. peptidereconstitutecalculator.com covers only BPC-157 and is not useful for GLP-1 work.
Is the FormBlends calculator only useful if I buy from FormBlends?
No. The calculator is free, requires no account, and does not require any purchase. It works the same way regardless of where your peptides came from. The mobile app version adds logging and a compound reference library, also free. FormBlends being a pharmacy company means the tool has a named, verifiable owner, which is more than most anonymous calculator pages can say.
Why do some calculators recommend a specific BAC water volume instead of letting me enter my own?
PeptideFox does this deliberately: it back-calculates a water volume that produces a round unit number on a standard syringe, which reduces drawing errors. The tradeoff is that you’re working backward from a convenient unit draw rather than from a water volume you may have already used. If you’ve already reconstituted the vial with a different amount, you need a calculator that accepts your actual water volume as the input, not a suggested one.
*These tools calculate how to measure a dose, not what dose to take. Always get that from a qualified medical provider.*
Sources
- U.S. Pharmacopeial Convention (USP), insulin syringe unit standards
- peptidefox.com, feature descriptions, verified 2025
- FormBlends mobile app listing, iOS App Store and Google Play, verified 2025
- peptides.org, dosage reference charts, verified 2025
- LeadWest Medical online calculator, verified 2025
