Amino Acid Chart: All 20 Standard Amino Acids
Name, 3-letter and 1-letter codes, side-chain classification, and molecular weight for every standard amino acid, grouped by side-chain property.
| Amino Acid | 3-letter | 1-letter | Classification | Formula | MW (g/mol) |
|---|---|---|---|---|---|
| Glycine | Gly | G | Nonpolar (aliphatic) | C2H5NO2 | 75.07 |
| Alanine | Ala | A | Nonpolar (aliphatic) | C3H7NO2 | 89.09 |
| Valineessential | Val | V | Nonpolar (aliphatic) | C5H11NO2 | 117.15 |
| Leucineessential | Leu | L | Nonpolar (aliphatic) | C6H13NO2 | 131.18 |
| Isoleucineessential | Ile | I | Nonpolar (aliphatic) | C6H13NO2 | 131.18 |
| Proline | Pro | P | Nonpolar (aliphatic) | C5H9NO2 | 115.13 |
| Methionineessential | Met | M | Nonpolar (aliphatic) | C5H11NO2S | 149.21 |
| Phenylalanineessential | Phe | F | Aromatic | C9H11NO2 | 165.19 |
| Tyrosine | Tyr | Y | Aromatic | C9H11NO3 | 181.19 |
| Tryptophanessential | Trp | W | Aromatic | C11H12N2O2 | 204.23 |
| Serine | Ser | S | Polar (uncharged) | C3H7NO3 | 105.09 |
| Threonineessential | Thr | T | Polar (uncharged) | C4H9NO3 | 119.12 |
| Cysteine | Cys | C | Polar (uncharged) | C3H7NO2S | 121.15 |
| Asparagine | Asn | N | Polar (uncharged) | C4H8N2O3 | 132.12 |
| Glutamine | Gln | Q | Polar (uncharged) | C5H10N2O3 | 146.15 |
| Aspartic acid | Asp | D | Acidic (negative) | C4H7NO4 | 133.10 |
| Glutamic acid | Glu | E | Acidic (negative) | C5H9NO4 | 147.13 |
| Lysineessential | Lys | K | Basic (positive) | C6H14N2O2 | 146.19 |
| Arginine | Arg | R | Basic (positive) | C6H14N4O2 | 174.20 |
| Histidineessential | His | H | Basic (positive) | C6H9N3O2 | 155.16 |
What This Chart Shows
Every protein in every living thing is built from some combination of these 20 amino acids, each linked to the next by a peptide bond. What makes each one different -- and gives a folded protein its shape and function -- is its side chain (R group): the part of the molecule that varies from one amino acid to the next while the backbone (amino group, carboxyl group, central carbon) stays the same.
The classification column groups amino acids by that side chain's chemistry: nonpolar aliphatic chains stay buried away from water inside a folded protein; aromatic side chains carry a ring structure; polar uncharged chains can hydrogen-bond with water but carry no net charge; and acidic and basic side chains are negatively or positively charged at physiological pH.
Worked example: verifying a molecular weight
Glycine, the simplest amino acid, has the formula C2H5NO2.
Paste C2H5NO2 into the Molar Mass Calculator and it breaks the formula down atom by atom -- 2 carbon, 5 hydrogen, 1 nitrogen, 2 oxygen -- and sums to the same 75.07 g/mol listed above, since both use the same IUPAC atomic weights.
Common mistake
Assuming every amino acid with an -OH or -NH2 group in its side chain is charged. Serine and threonine have a hydroxyl group and asparagine and glutamine have an amide group, but none of the four carry a net charge at physiological pH -- they're polar, not charged. Only aspartate, glutamate (negative) and lysine, arginine, histidine (positive) actually carry charge.
Keep going
- Every amino acid above is encoded by one or more mRNA triplets during translation. See exactly which codons map to which amino acid, plus the start and stop codons, in the Codon Chart
- A side chain's polarity or charge ultimately comes down to how strongly its atoms pull on shared electrons -- oxygen and nitrogen (common in polar, acidic and basic side chains) are both far more electronegative than carbon and hydrogen. Compare every element's pull with the Electronegativity Chart
- Every molecular weight above was cross-checked by re-deriving it from the amino acid's formula with this site's own Molar Mass Calculator
- Once you know an amino acid's molecular weight, you can convert a mass of it into moles and then into a solution concentration with the Molarity Calculator
Frequently Asked Questions
What are the 20 standard amino acids?
They're the 20 amino acids directly encoded by the genetic code (each has at least one mRNA codon) and used to build essentially every protein in every living organism. They're also called proteinogenic amino acids, to distinguish them from other amino acids (like ornithine or GABA) that exist in biochemistry but aren't used to build proteins from a codon.
What's the difference between the 3-letter and 1-letter codes?
Both are shorthand for the full amino acid name. The 3-letter code (like Gly or Trp) is easier to read and is common in biochemistry writing; the 1-letter code (like G or W) is used almost everywhere protein sequences are written out in full, since spelling a 300-amino-acid protein with 3-letter codes would be unwieldy.
Why does this chart classify amino acids into 5 groups instead of just acidic/basic/neutral?
The 5-group scheme (nonpolar aliphatic, aromatic, polar uncharged, acidic, basic) is the standard classification from Lehninger's Principles of Biochemistry, and it captures more than charge alone -- it also separates out the aromatic, ring-containing side chains (Phe, Tyr, Trp), which behave differently in a protein's structure than a plain nonpolar chain does even though none of the three carry a charge.
Is histidine acidic or basic?
Basic, by convention -- but a weak one. Histidine's imidazole side chain has a pKa near 6, close to physiological pH, so it's only partially protonated (positively charged) inside a cell, unlike lysine and arginine, which are essentially always protonated. It's still grouped with the basic amino acids because its side chain can accept a proton, just less reliably than the other two.
What does 'essential' mean in the amino acid table?
An essential amino acid is one the human body can't synthesize on its own in adequate amounts, so it has to come from food. There are 9: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. The other 11 are 'nonessential' only in the dietary sense -- your body can still make them, usually from other amino acids or metabolic intermediates.
Where do these molecular weights come from?
Each amino acid's molecular weight is computed directly from its molecular formula (cross-checked against NCBI PubChem) using the same IUPAC Standard Atomic Weights this site's Molar Mass Calculator uses -- so every number here is independently reproducible, not copied from an outside table.
Sources: NCBI PubChem (per-amino-acid compound records, for each standard amino acid's molecular formula) (https://pubchem.ncbi.nlm.nih.gov/, fetched 2026-09-25); Classification scheme: Lehninger Principles of Biochemistry, side-chain property groups (nonpolar aliphatic / aromatic / polar uncharged / acidic / basic) (https://www.ncbi.nlm.nih.gov/books/NBK21154/, fetched 2026-09-25).
Related Calculators
- Molarity Calculator — Solutions & Concentration
- Dilution Calculator — Solutions & Concentration
- Molality Calculator — Solutions & Concentration
- Molar Mass Calculator — Atomic & Molecular