Research Tool
Peptide Calculator
A mathematical reference tool for calculating reconstitution concentrations, syringe volumes, and aliquots per vial. Select your parameters below to see computed results.
Below the reconstitution calculator you will find the rest of the bench maths — dilution series, mass-to-molarity conversion, aliquot and storage planning, and the sequence-derived properties that decide how a peptide has to be handled.
2 units
of 30 unit syringe
Quick Reference
Syringe Size
Select the total volume of your syringe.
Peptide Vial Quantity
Total amount of peptide in the vial (in milligrams).
Bacteriostatic Water
Volume of bacteriostatic water used for reconstitution (in milliliters).
Desired Amount per Aliquot
Amount of peptide per individual aliquot (in micrograms).
Syringe
2 units
of 30 unit syringe
Concentration
5mg/mL
Volume per Aliquot
0.02mL
Aliquots per Vial
50aliquots
Quick Reference
This calculator is an educational reference tool for standard unit conversions. It does not constitute medical advice or administration recommendations. All Eppix Labs products are sold strictly for in-vitro research and laboratory use.
Lab Tool
Dilution Planner
Work out a single working dilution from a stock, or lay out a full serial dilution series with the transfer and diluent volume for every tube. The planner flags transfers that fall below the volume a standard pipette can measure reliably — the most common silent source of error in a dilution series.
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
Lab Tool
Mass ↔ Molarity Converter
Vials are labelled in milligrams; assay protocols and published binding data are in molar units. Convert between them for any compound of known molecular weight, correct for net peptide content, and see where the resulting concentration lands on a log scale from nanomolar to millimolar.
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
Lab Tool
Aliquot & Storage Planner
Split one reconstituted vial into single-use aliquots so a stock is thawed once rather than a dozen times. The planner shows the mass in each tube, how much dead volume costs you across the whole set, and the temperature bands that govern how long the material stays intact.
mass per aliquot = (peptide ÷ reconstitution volume) × aliquot volume
Aliquot rack
10 × 200 µLthe vial divides evenly
Volume per aliquot
200µL
Peptide per aliquot
1.00mg
Concentration
5.00mg/mL
Recoverable per tube
975mcg
2.5 % held back as dead volume
Storage temperature & expected stability
- Lyophilised
- Weeks — shipping window only
- In solution
- Hours — working session only
- Lyophilised
- Months
- In solution
- 2–4 weeks in bacteriostatic water
- Lyophilised
- 1–2 years
- In solution
- 1–3 months as single-use aliquots
- Lyophilised
- 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 oxidise faster than the table suggests; protect those from light and headspace oxygen.
Lab Tool
Sequence Property Analyser
Paste a one-letter sequence to get molecular weight, isoelectric point, net charge across the whole pH range, hydropathy, and the 280 nm extinction coefficient. Together these answer the two questions that come up before any peptide goes into solution: which solvent, and which buffer pH to stay away from.
One-letter sequence
Residues — 15 total
Composition
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 -2.06Net charge vs pH
pH 7.4 → -2.06x: pH · y: net charge · drag or hover to read the curve
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.
Reference Information
Understanding Reconstitution Math
Concentration Formula
Concentration (mg/mL) = Peptide Amount (mg) ÷ Water Volume (mL). For example, 10 mg of peptide reconstituted in 2 mL of bacteriostatic water yields a concentration of 5 mg/mL.
Syringe Unit Conversion
Standard insulin syringes are marked in “units.” A 1 mL syringe has 100 units, a 0.5 mL syringe has 50 units, and a 0.3 mL syringe has 30 units. Each unit equals 0.01 mL regardless of syringe size.
Aliquots Per Vial
Total aliquots = Total Peptide (mcg) ÷ Desired Amount (mcg). This tells you how many equal measurements can be obtained from a single vial at the selected amount.
Dilution (C₁V₁ = C₂V₂)
The amount of compound in a sample does not change when you dilute it, only the volume it is spread through. Rearranged, V₁ = (C₂ × V₂) ÷ C₁ gives the volume of stock to transfer; the balance of the final volume is diluent. Units cancel, so the two concentrations only need to match each other.
Serial Dilution
Repeating a fixed-factor dilution down a row of tubes gives Cₙ = C₀ ÷ fⁿ, where f is the factor and n the step number. Each step transfers V ÷ f from the previous tube into V − (V ÷ f) of diluent. Because the error at each step multiplies rather than adds, a series is only as good as its smallest transfer.
Mass to Molarity
Moles = mass (g) ÷ molecular weight (g/mol), and molarity (M) = moles ÷ volume (L). Because peptide molecular weights range from a few hundred to several thousand daltons, two vials holding the same milligram figure can differ tenfold in molar concentration.
Net Peptide Content
A lyophilised powder is not pure peptide: counter-ions (acetate or TFA), residual water and salts make up part of the weight. Powder to weigh = required peptide mass ÷ net peptide content. At 80 % net content, 1 mg of peptide means weighing 1.25 mg of powder.
Isoelectric Point and Solubility
The pI is the pH at which a peptide’s positive and negative charges cancel. At that point there is no electrostatic repulsion between molecules, so solubility is at its minimum and aggregation at its most likely. Keeping the working buffer at least one pH unit away from the pI is the single most effective thing you can do to get a stubborn peptide into solution.
Concentration by A₂₈₀
Tryptophan and tyrosine absorb at 280 nm, with molar extinction coefficients of 5500 and 1490 M⁻¹cm⁻¹ respectively. Summing them gives ε₂₈₀ for the peptide, and A₂₈₀ ÷ (ε ÷ MW) returns mg/mL in a 1 cm path. A peptide with neither residue is effectively invisible at 280 nm and needs a different assay.
Glossary
Key Terms
Lyophilized Peptide
A freeze-dried peptide powder, stored in a sealed vial prior to reconstitution.
Bacteriostatic Water
Sterile water containing 0.9% benzyl alcohol as a preservative, commonly used for reconstitution.
Reconstitution
The process of adding a solvent (e.g. bacteriostatic water) to a lyophilized compound to return it to solution.
Concentration (mg/mL)
The amount of peptide per milliliter of solution after reconstitution.
mcg (Microgram)
One millionth of a gram (1/1000 of a milligram). A common unit for measuring peptide amounts.
IU / Units
Markings on insulin syringes. 100 units = 1 mL. Used to measure small volumes accurately.
Molarity (M)
Moles of solute per litre of solution. The unit assay protocols and binding data are written in, unlike the milligrams on a vial label.
Molecular Weight (Da)
Mass of one mole of the compound, in daltons (numerically identical to g/mol). The bridge between milligrams and moles.
Serial Dilution
A chain of fixed-factor dilutions, each made from the tube before it, used to span several orders of magnitude in concentration.
Dead Volume
Liquid that stays behind on tube walls and in pipette tips and is never recovered. Small per transfer, significant across a whole set of aliquots.
Net Peptide Content
The fraction of a lyophilised powder that is actually peptide, the rest being counter-ions, water and salts. Typically 70–90 % for acetate or TFA salts.
Isoelectric Point (pI)
The pH at which net charge is zero. Solubility is at its minimum here, so buffers within about one pH unit of the pI are best avoided.
GRAVY
Grand average of hydropathy — the mean Kyte–Doolittle score across the sequence. Positive values indicate a net hydrophobic peptide that may need an organic co-solvent.
ε₂₈₀ / A₂₈₀
Molar extinction coefficient at 280 nm and the absorbance it produces. Used to confirm a stock concentration without consuming the sample.
Freeze–Thaw Cycle
One round of freezing and thawing a stock. Each cycle is a chance for the peptide to aggregate or degrade, which is why single-use aliquots are preferred.
Reference Table
Molecular Weights
Average molecular weights for compounds commonly handled alongside this catalogue, given for the free (non-salt) form. Counter-ions add mass to the weighed powder — that difference is what the net peptide content field in the molarity converter accounts for.
| Compound | MW (Da) | Notes |
|---|---|---|
| BPC-157 | 1419.53 | Sequence: GEPPPGKPADDAGLV |
| TB-500 (Thymosin β4) | 4963.44 | Sequence: SDKPDMAEIEKFDKSKLKKTETQEKNPLPSKETIEQEKQAGES |
| GHK-Cu | 403.93 | Copper complex; GHK free tripeptide is 340.38 Da. |
| KPV | 342.44 | Sequence: KPV |
| Ipamorelin | 711.85 | Contains non-standard residues (Aib, 2-Nal). |
| CJC-1295 (no DAC) | 3367.86 | Also sold as Mod GRF 1-29. |
| Tesamorelin | 5135.87 | — |
| Semax | 813.93 | Sequence: MEHFPGP |
| Selank | 751.88 | Sequence: TKPRPGP |
| Epitalon | 390.35 | Sequence: AEDG |
| Melanotan II | 1024.18 | Cyclic; contains D-Phe and Nle. |
| PT-141 (Bremelanotide) | 1025.16 | — |
| MOTS-c | 2174.56 | Sequence: MRWQEMGYIFYPRKLR |
| SS-31 | 639.79 | Contains D-Arg and Dmt. |
| Thymosin α-1 | 3108.33 | N-terminally acetylated in the native form. |
| AOD-9604 | 1817.09 | — |
| Kisspeptin-10 | 1302.51 | Sequence: YNWNSFGLRF |
| DSIP | 848.81 | Sequence: WAGGDASGE |
| IGF-1 LR3 | 9117.50 | 83-residue analogue. |
| Tirzepatide | 4813.45 | — |
| Retatrutide | 4731.32 | — |
| Cagrilintide | 3748.20 | — |
| NAD+ | 663.43 | Dinucleotide, not a peptide. |
| Glutathione (reduced) | 307.32 | γ-linked at Glu; sequence shown for composition only. |
Figures are calculated or literature average masses for reference only. Where a compound contains non-standard residues or modifications, the sequence column is omitted because the one-letter code cannot represent it faithfully. Always confirm against the certificate of analysis for the specific lot in hand.