The math people get wrong most often is the swap between mg and mcg. A 5 mg vial reco'd with 1 mL of BAC water gives you 5,000 mcg/mL. Same vial with 2 mL? 2,500 mcg/mL. Pin the same units on the slin pin and you've just halved your dose without noticing. It looks obvious typed out. It is not obvious at 11pm on pin day with a new lyo vial in your hand and three unit systems running in your head at once.
The free Next Pep dosing calculator settles this in one screen, drop in vial mg, BAC water volume, target dose, and you get exact draw volume in mL plus the unit mark on a 100u slin pin. No signup. Works for anything in the library or any custom compound.
Key Takeaways
- —FDA enforcement data (2025) flagged up to 40% of online peptides as incorrectly dosed, the risk starts at the vendor and compounds at reco.
- —The reco formula isn't hard: concentration (mcg/mL) = vial mg × 1,000 ÷ BAC water mL. Where it goes wrong is execution.
- —100u slin pins measure volume (100 units = 1 mL), not mass, so "10 units" means nothing until you know your concentration.
- —BWFI / BAC water (0.9% benzyl alcohol) is the standard reco diluent. Reco'd vial holds 28 days at 2 to 8°C.
- —The Next Pep calculator is free, runs in the browser, and auto-loads sensible vial defaults for anything in the research library.
Research peptides ship as lyo powder, freeze-dried in vials at 1, 2, 5, or 10 mg, that's the standard line-up. Lyo strips out >99% of moisture, which is why a quality lyo vial holds at -20°C for 3 to 5 years untouched. The powder isn't usable as-is. You have to reco it in sterile diluent before you can pin anything.
The diluent is BAC water (BWFI), sterile water with 0.9% benzyl alcohol as the preservative. The benzyl alcohol is what gives a reco'd vial its 28-day shelf life at 4°C, it keeps bacteria out. Plain sterile water or saline works for one-and-done prep, but it doesn't preserve, so single-use only.
Reco is just volumetric dilution math. Two things make it bunk-prone in practice:
It's a three-step calc:
Step 1, concentration: mcg/mL = vial mg × 1,000 ÷ BAC water mL
Step 2, draw volume: mL = target dose mcg ÷ concentration mcg/mL
Step 3, slin pin units: units = mL × 100 (on a 100u slin pin, the standard)
Step 1: 5 × 1,000 ÷ 2 = 2,500 mcg/mL Step 2: 250 ÷ 2,500 = 0.1 mL Step 3: 0.1 × 100 = 10 units on the slin pin
Draw to the 10u mark, every time, on that vial.
Change any input and the answer moves with it. Same vial reco'd with 1 mL doubles concentration to 5,000 mcg/mL, your 250 mcg dose is now at the 5u mark. Reco the same vial with 4 mL and the concentration halves to 1,250 mcg/mL, putting your 250 mcg at the 20u mark. Nothing else moves the answer.
The newbie trap nobody flags: vial says 5 mg, that's TOTAL in the vial, not per dose. Plenty of people on r/Peptides have pinned their first ever 5 mg dose because they assumed "5 mg vial" meant "5 mg per pin". Don't be that person. The vial is a bulk amount you split across many doses.
Past unit-conversion errors, these are the five failure modes that come up over and over in newbie threads:
The Next Pep calculator at /dosing-calculator handles all of this in one screen. Three inputs:
Four outputs:
No signup. Runs in your browser. The calc auto-loads sensible vial size and dose defaults for any peptide in the research library, so if you're working BPC-157, TB-500, tirz, ipa, sermorelin, GHK-Cu, PT-141, or any of 60+ other compounds, the defaults are pre-filled.
Reco'd vials hold at 2 to 8°C (regular fridge temp) for 28 days. Two rules that actually matter on pin day:
Date the vial on first puncture. A sticker or a permanent marker on the cap. Past 28 days from that date, dump it, doesn't matter how clean it looks. The 28-day rule is chemistry, not vibes.
Most protocols go 2 mL into a 5 mg vial, which gets you 2,500 mcg/mL. That gives clean unit marks for common doses (250 mcg = 10u, 500 mcg = 20u). Some people run 1 mL for double concentration if they want smaller draw volumes. The Next Pep calculator shows both side-by-side so you can see which suits your dose.
For single-use only, sure. Any vial you'll touch more than once needs the 0.9% benzyl alcohol in BWFI as the preservative, without it your reco'd vial has a 24 to 72 hour shelf life, not 28 days. For research protocols where you're pinning out of the same vial across weeks, BAC water is the only call.
Depends entirely on the concentration in your vial. On a 100u slin pin, 10 units = 0.1 mL. A vial at 2,500 mcg/mL delivers 250 mcg in that 0.1 mL. A vial at 5,000 mcg/mL delivers 500 mcg. Recalculate every time the vial changes, the calculator tells you exactly what each unit mark is worth in mcg.
28 days refrigerated at 2 to 8°C is the standard rule. Stability varies by peptide, BPC-157 is unusually stable, others go faster, but the 28-day cutoff covers everything safely. Don't use a reco'd vial past 28 days even if it looks fine. Stability is chemistry, not eyeballs.
Yep, fully free, no signup, browser-based. The dosing calculator works with anything in the research library or any custom compound you enter. We don't sell peptides and we don't have any vendor affiliations, the calculator is a research tool, not a lead capture.
This article is for research and informational purposes only. Research peptides aren't FDA-approved for human clinical use.
Research Disclaimer. All content on Next Pep is for informational and educational purposes only. It does not constitute medical advice, diagnosis, or treatment. Consult a licensed healthcare professional before considering any peptide protocol.
CJC-1295 with DAC has a 6-8 DAY half-life; Modified GRF (1-29) clears in ~30 minutes. Same modified GHRH(1-29) backbone, one bolt-on linker, ~1,000x PK difference.
TB-500 is a 7-aa fragment of thymosin beta-4 (43 aa, ~4,963 Da), not the full protein. Cross-COA review: ~67% of "TB-500" vials are actually full Tβ4.