Peptide Molecular Weight Calculator
Calculate the molecular weight (Da and kDa), net charge at pH 7.4, and sequence length for any peptide using single-letter amino acid codes.
Use single-letter amino acid codes (A, C, D, E, F, G, H, I, K, L, M, N, P, Q, R, S, T, V, W, Y). Spaces and line breaks are ignored.
— Molecular Weight (Da)
— Molecular Weight (kDa)
— Net Charge (pH 7.4)
— Amino Acids
Amino Acid Single-Letter Reference
Standard IUPAC single-letter codes for the 20 standard amino acids and their average molecular weights.
| Code | Amino Acid | Avg MW (Da) |
|---|---|---|
| A | Alanine | 89.09 |
| R | Arginine | 174.2 |
| N | Asparagine | 132.12 |
| D | Aspartic acid | 133.1 |
| C | Cysteine | 121.16 |
| E | Glutamic acid | 147.13 |
| Q | Glutamine | 146.15 |
| G | Glycine | 75.03 |
| H | Histidine | 155.16 |
| I | Isoleucine | 131.17 |
| L | Leucine | 131.17 |
| K | Lysine | 146.19 |
| M | Methionine | 149.21 |
| F | Phenylalanine | 165.19 |
| P | Proline | 115.13 |
| S | Serine | 105.09 |
| T | Threonine | 119.12 |
| W | Tryptophan | 204.23 |
| Y | Tyrosine | 181.19 |
| V | Valine | 117.15 |
Frequently Asked Questions
Molecular weight (MW) of a peptide is the sum of atomic masses of all atoms in the molecule, expressed in Daltons (Da) or kilodaltons (kDa). It is calculated from the amino acid residue masses minus water for each peptide bond.
Sum the average residue masses of each amino acid, subtract 18.02 Da per peptide bond (n-1 bonds for n residues), then add 18.02 Da for the terminal water. Our calculator handles all of this automatically.
Net charge is the sum of all ionizable group charges at a given pH. At pH 7.4, basic residues (K, R, H) contribute positive charge and acidic residues (D, E, C, Y) contribute negative charge.
kDa refers to molecular weight, not charge. A "negatively charged" peptide means it has more acidic residues than basic ones at the pH being measured. This is independent of molecular size.
kDa = kilodalton = 1000 Daltons. BPC-157 is approximately 1.42 kDa. Most research peptides are 0.5–5 kDa. Larger proteins are typically described in kDa for convenience.