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Research Peptide Calculator: Stock Concentration, Molarity, Dilution, Aliquot and Sequence Tools

Five connected calculators for preparing research peptide solutions. Start from the mass on the vial and the volume of diluent, then carry that stock through a molar conversion, a working dilution and an aliquot split. A sequence tool estimates molecular weight, pI and 280 nm absorbance. Every result recalculates as you type, and no input leaves your device.

Stock solution1 of 7

Step A — Make the stock

Stock Concentration & Draw Volume Calculator

Set the labeled peptide mass and the diluent volume you added. Enter a target mass in µg to see the draw volume that holds it on a graduated µL/mL gauge, plus how many draws one vial yields.

0 µL10 µL20 µL30 µL40 µL50 µL

50 µL

on a 50 µL scale

Research solution, pipette.

Concentration5mg/mL
Draw Volume50µL
Draws / Vial40draws
Per 100 µL500µg

C = 10 mg ÷ 2 mL = 5 mg/mL  ·  V = 250 µg ÷ 5000 µg/mL = 50 µL

Volume for Neighboring Masses

125 µg25 µL
250 µg50 µL
500 µg100 µL

Worked example: 5 mg vial, 2.5 mL diluent

  1. 5 mg ÷ 2.5 mL = 2 mg/mL (2,000 µg/mL)
  2. 150 µg ÷ 2,000 µg/mL = 0.075 mL = 75 µL
  3. Net content 104% → 5.2 mg ÷ 2.5 mL = 2.08 mg/mL → 72.1 µL

Draw volumes here describe pipetting a laboratory solution and nothing else. Swap the labeled mass for the measured figure on the lot’s certificate of analysis whenever you have it. For preparation technique, see the reconstitution lab guide.

Step B — Count the molecules

Mass-to-Molarity Converter (mg ↔ mM)

Turn a milligram figure in a known volume into a molar concentration, or work backward from a target molarity to the mass you need to weigh. 24 built-in compounds use free-peptide molecular weights.

moles = mass (g) ÷ MW (g/mol)  ·  molarity (M) = moles ÷ volume (L)

Prepared vial

2.50 mg/mL

2 mL fill

Molar concentration

1.761mM

Total substance

3.522µmol

Mass concentration

2.500mg/mL

Powder to weigh

5.000mg

Equal to peptide mass at 100 % net content.

Where this lands · log scale

1.761 mM
1 nM10 nM100 nM1 µM10 µM100 µM1 mM10 mM100 mM

Worked example: 5 mg Selank in 1 mL

  1. 5 mg = 0.005 g; MW 751.88 g/mol
  2. 0.005 g ÷ 751.88 g/mol = 6.65 µmol
  3. 6.65 µmol ÷ 0.001 L = 6.65 mM

Step C — Bring it to working strength

Working Dilution & Serial Series (C₁V₁ = C₂V₂)

Give the stock strength, the strength you want and the final volume; the planner returns how much stock to pipette and how much diluent makes up the rest. Serial mode repeats one factor down a row of tubes.

C₁ × V₁ = C₂ × V₂  →  V₁ = (C₂ × V₂) ÷ C₁

Transfer

Stock

10 mg/mL

Working

1 mg/mL

dashed line = stock aliquot

Stock to transfer

0.1mL

100 µL

Diluent to add

0.9mL

Dilution factor

1 : 10

Worked example: 2 mg/mL down to 0.25 mg/mL, 2 mL final

  1. V₁ = (0.25 mg/mL × 2 mL) ÷ 2 mg/mL = 0.25 mL
  2. Transfer 250 µL stock + 1,750 µL diluent
  3. Serial, factor 4: 2 → 0.5 → 0.125 → 0.031 mg/mL

Step D — Split before storing

Aliquot Split & Cold-Storage Planner

Divide one stock into equal tubes by count or by fixed volume. The planner subtracts the dead volume lost in every tube and lays out typical stability windows from the refrigerator to −80 °C.

mass per aliquot = (peptide ÷ reconstitution volume) × aliquot volume

Aliquot rack

10 × 200 µL

the vial divides evenly

Volume per aliquot

200µL

Peptide per aliquot

1.00mg

Concentration

5.00mg/mL

Recoverable per tube

975µg

2.5 % held back as dead volume

Why aliquot at allA stock that is thawed and refrozen for every experiment goes through that stress once per use; single-use aliquots go through it once, full stop. Label each tube with the compound, concentration and date, freeze upright, and thaw on ice rather than at room temperature.

Storage temperature & expected stability

+20 °CAmbient
Lyophilized
Weeks — shipping window only
In solution
Hours — working session only
+4 °CRefrigerated
Lyophilized
Months
In solution
2–4 weeks in solution
−20 °CFreezer
Lyophilized
1–2 years
In solution
1–3 months as single-use aliquots
−80 °CUltra-low
Lyophilized
Several years
In solution
6–12 months as single-use aliquots

Ranges are general handling guidance for research peptides and are not a substitute for the stability data on a specific certificate of analysis. Peptides containing Met, Cys or Trp oxidize faster than the table suggests; protect those from light and headspace oxygen.

Worked example: 5 mg in 2.5 mL, 10 tubes, 15 µL dead volume

  1. 2.5 mL ÷ 10 = 250 µL per tube, 0.5 mg each
  2. Recoverable: 250 − 15 = 235 µL → 0.47 mg per tube
  3. Lost to dead volume across the set: 0.3 mg

Stability windows are typical ranges, not lot data. Thaw each tube once and discard the remainder. More detail is in the peptide storage guide.

Step E — Read the sequence

Sequence MW, pI & Hydropathy Estimator

Enter a one-letter amino acid sequence to estimate average molecular weight, isoelectric point, charge at pH 7, GRAVY score and the 280 nm extinction coefficient. It assumes linear L-residues, free termini and no disulfide bonds.

One-letter sequence

Residues — 15 total

GEPPPGKPADDAGLV

Composition

Basic (+)1 · 7%Acidic (−)3 · 20%Polar0 · 0%Hydrophobic4 · 27%Structural7 · 47%

Residues

15aa

Molecular weight

1419.55Da

Average mass, free acid, unmodified termini.

Isoelectric point

3.88pI

Estimated from side-chain pKa values.

Net charge · pH 7

-2.02

GRAVY

-0.693

Negative — net hydrophilic.

ε₂₈₀ (reduced)

0M⁻¹cm⁻¹

Buffer pH

pH 7.4 · net charge -2.06
0714

Net charge vs pH

pH 7.4 → -2.06
pI 3.88
pH 7.4 · -2.06

x: pH · y: net charge · drag or hover to read the curve

Solvent selectionAcidic peptide — dissolve in a slightly basic aqueous bufferWith an estimated pI below 6 the peptide carries net negative charge at neutral pH and is most soluble above its pI. Sterile water or a dilute basic buffer (e.g. 0.1 M ammonium bicarbonate) is the usual first attempt. Add solvent slowly down the vial wall and swirl — never vortex or shake.Avoid buffers between pH 2.9 and 4.9.

Concentration check by A₂₈₀

No tryptophan or tyrosine, so this peptide has essentially no absorbance at 280 nm and A₂₈₀ cannot be used to check its concentration. Use a colorimetric assay (BCA) or quantitative amino-acid analysis instead — a reading at 205–214 nm on the peptide bond is possible but far more sensitive to buffer interference.

Values are computed from the primary sequence assuming free (unmodified) N- and C-termini, all cysteines reduced, and standard L-amino acids. Acetylation, amidation, cyclisation, non-standard residues and counter-ions all shift the real figures — treat these as a starting point, not as a certificate of analysis.

Worked example: Kisspeptin-10 (YNWNSFGLRF)

  1. 10 residues, average MW 1,302.5 g/mol
  2. One Trp (5,500) + one Tyr (1,490) → ε₂₈₀ = 6,990 M⁻¹cm⁻¹
  3. A₂₈₀ of a 1 mg/mL solution ≈ 6,990 ÷ 1,302.5 ≈ 5.37

Reference

Molecular Weights Used by the Converter

Average masses for the free peptide, without counter-ions. Acetate or TFA salt forms weigh more per mole of peptide, which is exactly what the net content input corrects for.

MW (g/mol)CompoundSequence / note
1,419.53BPC-157GEPPPGKPADDAGLV
4,963.44TB-500 (Thymosin β4)SDKPDMAEIEKFDKSKLKKTETQEKNPLPSKETIEQEKQAGES
402.92GHK-CuCopper complex; GHK free tripeptide is 340.38 Da.
342.44KPVKPV
711.85IpamorelinContains non-standard residues (Aib, 2-Nal).
3,367.86CJC-1295 (no DAC)Also sold as Mod GRF 1-29.
5,135.87Tesamorelin—
813.93SemaxMEHFPGP
751.88SelankTKPRPGP
390.35EpitalonAEDG
1,024.18Melanotan IICyclic; contains D-Phe and Nle.
1,025.16PT-141 (Bremelanotide)—
2,174.56MOTS-cMRWQEMGYIFYPRKLR
639.79SS-31Contains D-Arg and Dmt.
3,108.33Thymosin α-1N-terminally acetylated in the native form.
1,817.09AOD-9604—
1,302.51Kisspeptin-10YNWNSFGLRF
848.81DSIPWAGGDASGE
9,117.50IGF-1 LR383-residue analogue.
4,813.45Tirzepatide—
4,731.32Retatrutide—
4,409.00Cagrilintide—
663.43NAD+Dinucleotide, not a peptide.
307.32Glutathione (reduced)γ-linked at Glu; sequence shown for composition only.

Where a compound contains modified or non-standard residues, a note replaces the sequence. For the lot in hand, rely on its certificate of analysis.

Before you pipette

Calculator FAQ

Solution arithmetic, not instructions for use.

These tools convert between µg, mg, mL and mM and balance volumes for laboratory work. Nothing on this page is medical advice or a protocol. Eppix Labs products are for in vitro research only; they are not FDA-approved and are not for human or veterinary use.

A microliter (µL) is a fixed SI volume: 1,000 µL is exactly 1 mL, and pipettes are calibrated against it. A "unit" is not a volume at all, and its meaning changes with whatever it is marked on. Reporting draw volume in µL or mL keeps every result traceable to a calibrated instrument.

Find the measured peptide mass reported for the lot and divide it by the labeled mass, then multiply by 100. A 10 mg vial measured at 10.6 mg is 106%; one measured at 9.4 mg is 94%. Always use the certificate of analysis for the specific lot in front of you, since the figure varies between lots.

No more than your least precise input supports. The calculator rounds concentration to 0.01 mg/mL and volume to 0.1 µL, but if the diluent was measured to ±0.05 mL, the last digit is not meaningful. Most air-displacement pipettes lose accuracy below about 10% of their rated range, so choose a stock concentration that keeps each draw volume well inside it.

Molarity counts molecules, and heavier molecules mean fewer of them per milligram. At 2 mg/mL, Epitalon (390.35 g/mol) is about 5.12 mM, while Tesamorelin (5,135.87 g/mol) is about 0.39 mM, roughly a thirteenfold gap at identical mass concentration.

Dead volume is the liquid left behind on tube walls and in pipette tips that is never recovered; the planner subtracts it so the mass per tube reflects what can actually be transferred. The page is not a guide to using peptides. It is solution arithmetic for laboratory work only: the products are not FDA-approved and are not for human or veterinary use.

Terms on This Page

Stock solution
The concentrated solution made directly from the vial, from which every working dilution is drawn.
Draw volume
The µL or mL of stock that contains a chosen mass of peptide at the current concentration.
Net content
Measured peptide mass as a percentage of the labeled mass, taken from the lot’s certificate of analysis.
Millimolar (mM)
One thousandth of a mole per liter. It depends on molecular weight, unlike mg/mL.
Dilution factor
Stock concentration divided by working concentration; a factor of 4 turns 2 mg/mL into 0.5 mg/mL.
Dead volume
Solution retained by tube walls and pipette tips that can never be transferred out.
Isoelectric point (pI)
The pH at which net charge is zero and a peptide is least soluble.
ε₂₈₀
How strongly a sequence absorbs 280 nm light, set by its tryptophan and tyrosine residues.

Replace the label mass with a measured one

Each lot’s certificate of analysis reports what the lab actually found in the vial. Enter that figure as net content and the stock math follows it.

Browse certificatesSee research peptides

Sold for in vitro laboratory research only. Not a drug, supplement or FDA-approved product, and not for human or veterinary use.