Research Terminology

Peptide Cheat Sheet: Every Number on One Page

The numbers people look up repeatedly, collected on one page — unit conversions, reconstitution math, storage windows and needle sizing.

Peptide Library Editorial · October 12, 2026 · 3 min read

This page collects the numbers that get looked up repeatedly. Nothing here is a protocol — these are conversions, limits and equipment specifications. Each section links to the full guide behind it.

1. Syringe units to millilitres

The single most common source of dosing errors. A U-100 insulin syringe is marked in insulin units, and 100 units is 1 mL.

Units on syringe	Volume	Fraction of 1 mL
5 units	0.05 mL	1/20
10 units	0.10 mL	1/10
20 units	0.20 mL	1/5
25 units	0.25 mL	1/4
50 units	0.50 mL	1/2
100 units	1.00 mL	Full syringe

Units are volume, not dose. The insulin unit is a volume marking that happens to correspond to an insulin activity unit — for every other peptide it means nothing except 0.01 mL. Full detail in the units-to-mL guide.

2. Reconstitution: concentration from vial and volume

Concentration = vial mass ÷ water added. Everything else follows from that one division.

Vial	Add 1 mL	Add 2 mL	Add 3 mL	Add 5 mL
2 mg	2000 mcg/mL	1000 mcg/mL	667 mcg/mL	400 mcg/mL
5 mg	5000 mcg/mL	2500 mcg/mL	1667 mcg/mL	1000 mcg/mL
10 mg	10 mg/mL	5 mg/mL	3.3 mg/mL	2 mg/mL
15 mg	15 mg/mL	7.5 mg/mL	5 mg/mL	3 mg/mL
50 mg	50 mg/mL	25 mg/mL	16.7 mg/mL	10 mg/mL

3. Volume to draw for a target amount

Volume = target ÷ concentration. Shown in syringe units, which is what you actually read.

Concentration	250 mcg	500 mcg	1 mg	2 mg
1000 mcg/mL	25 units	50 units	100 units	—
2500 mcg/mL	10 units	20 units	40 units	80 units
5000 mcg/mL	5 units	10 units	20 units	40 units
10 mg/mL	2.5 units	5 units	10 units	20 units

Aim for doses that land between 10 and 50 units. Below 5 units the marking error becomes a large fraction of the dose; above 50 you are wasting vial volume. If a dose falls outside that band, change the reconstitution volume rather than squinting at the barrel. The peptide calculator does this automatically.

4. Unit prefixes

Written	Means	In milligrams
1 g	gram	1000 mg
1 mg	milligram	1 mg
1 mcg / 1 µg	microgram	0.001 mg
1000 mcg	—	1 mg
250 mcg	—	0.25 mg

mcg and mg are a thousandfold apart and are the most consequential typo in this field. A protocol written in mcg and read as mg is a 1000× error.

5. Storage and stability

State	Temperature	Practical limit
Lyophilised, unopened	2–8 °C	Months to years per COA
Lyophilised, long term	−20 °C	Extends shelf life
Reconstituted	2–8 °C	Bounded by the 28-day BAC water limit
Reconstituted with sterile water	2–8 °C	Single use — no preservative
Any state	Room temperature	Minimise; hours not days
Reconstituted	Frozen	Avoid — freeze/thaw degrades peptides

The 28-day limit comes from the water, not the peptide. Benzyl alcohol at 0.9% is preserved for 28 days after first puncture. A peptide stable for longer is still bounded by its diluent. See the bacteriostatic water guide.

6. Needles

Gauge	Outer diameter	Typical use
18G	1.27 mm	Drawing diluent only — never for injection
21G	0.82 mm	Drawing from vials
25G	0.51 mm	Intramuscular
27G	0.41 mm	Subcutaneous
29G	0.34 mm	Subcutaneous, common on insulin syringes
30G	0.31 mm	Subcutaneous
31G	0.26 mm	Subcutaneous, shortest lengths

Higher gauge means thinner. Subcutaneous injection typically uses 29–31G at 4–8 mm. Full detail in the needle size guide and the injection sites guide.

7. Reported half-lives

Approximate, and the figure that determines whether a compound is dosed daily or weekly.

Peptide	Reported half-life	Implication
Semaglutide	~7 days	Once weekly
Tirzepatide	~5 days	Once weekly
Retatrutide	~6 days	Once weekly
Liraglutide	~13 hours	Once daily
Tesamorelin	~26–38 minutes	Daily; pulse-driven
Sermorelin	~11–12 minutes	Daily; very short
Ipamorelin	~2 hours	Pulse-driven
BPC-157	Not established in humans	No human PK data

Why half-life drives the schedule is covered in the peptide half-life guide.

8. Terms worth knowing

Term	Meaning
Lyophilised	Freeze-dried powder — the state peptides ship in
Reconstitution	Adding liquid to the powder
BAC water	Bacteriostatic water; 0.9% benzyl alcohol
COA	Certificate of analysis — purity and identity testing
HPLC	The chromatography method behind most purity figures
MS	Mass spectrometry — confirms identity, not just purity
RUO	Research use only — not for human or veterinary use
Subcutaneous (SC)	Into the fat layer under the skin
Intramuscular (IM)	Into muscle tissue

The full peptide terminology glossary expands on all of these, and the COA reading guide covers what an HPLC trace actually shows.

Research and educational use only. Peptide Library is an independent research and comparison platform and does not sell peptides. Nothing here is medical advice, dosing guidance, or a recommendation to administer any substance to a person or an animal. Consult a licensed clinician for anything concerning human health.

Sources

1. Bacteriostatic Water for Injection, USP — prescribing information (0.9% benzyl alcohol, multiple-dose use) — DailyMed / U.S. National Library of Medicine (2026) Source

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Peptide Library Editorial

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