Codon Translation Calculator
This calculator translates an mRNA nucleotide sequence into an amino acid sequence using the standard genetic code as defined by NCBI. Enter an mRNA sequence (A, U, G, C; T is treated as U) and the reading frame offset (0, 1, or 2 bases to skip at the start). The calculator reads triplet codons from left to right and maps each to its amino acid using the standard 64-codon table. Stop codons are displayed as asterisks. The output shows the full amino acid sequence in single-letter code, the number of codons, and the protein length in amino acids before the first stop codon.
Standard genetic code
64 codons (4^3) map to 20 amino acids + 3 stop codons.
Start codon: AUG (Met, M)
Stop codons: UAA (*), UAG (*), UGA (*)
The genetic code is nearly universal across life on Earth. Mitochondrial genomes use a slightly modified code (e.g., UGA encodes Trp instead of stop). This calculator uses the standard nuclear genetic code (NCBI translation table 1).
Reading the output
- Single-letter amino acid codes: M = Met, F = Phe, K = Lys, E = Glu, etc.
- An asterisk (*) marks a stop codon.
- Protein length counts amino acids before the first stop codon.
- If the sequence length is not divisible by 3 after frame offset, the last incomplete codon is ignored.
Frequently asked questions
What is a codon?
A codon is a sequence of three consecutive nucleotides in mRNA that encodes a specific amino acid (or a stop signal). The standard genetic code maps 64 codons (4^3 combinations of A, U, G, C) to 20 amino acids and 3 stop codons.
What are stop codons?
Stop codons signal the end of translation. The three standard stop codons in mRNA are UAA, UAG, and UGA. When a ribosome encounters a stop codon, it releases the polypeptide chain. This calculator marks stop codons as '*' in the output.
Does this calculator use DNA or mRNA sequence?
This calculator accepts mRNA sequence (A, U, G, C). If you enter a DNA template strand (with T instead of U), replace T with U before pasting, or use the DNA sense strand directly as the calculator automatically substitutes T for U.
What is the start codon?
The start codon AUG encodes methionine and marks the beginning of translation in most organisms. Translation begins at the first AUG in a suitable Kozak context. This calculator translates from the first base entered; select the correct reading frame.
What is reading frame?
A reading frame is one of three possible ways to divide an mRNA sequence into codons: starting at position 1, 2, or 3. A frameshift mutation shifts the reading frame, causing misreading of all downstream codons. This calculator reads from the start of your input in one frame.
Official sources
- NCBI: NCBI Genetic Codes (translation tables).
- NIH NCBI Bookshelf: The genetic code and protein synthesis.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.