Biology · Genetic code

Codon table chart and lookup.

Look up what a codon codes for, or which codons code for an amino acid, using the standard genetic code (NCBI table 1) in RNA or DNA letters.

64 codonsRNA or DNA lettersNCBI standard codeChecked 8 October 2026

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The standard genetic code, all 64 codons

Codon chart (NCBI table 1, Standard Code)
1st	2nd U	2nd C	2nd A	2nd G	3rd
U	UUU Phe	UCU Ser	UAU Tyr	UGU Cys	U
	UUC Phe	UCC Ser	UAC Tyr	UGC Cys	C
	UUA Leu	UCA Ser	UAA Ter	UGA Ter	A
	UUG Leu	UCG Ser	UAG Ter	UGG Trp	G
C	CUU Leu	CCU Pro	CAU His	CGU Arg	U
	CUC Leu	CCC Pro	CAC His	CGC Arg	C
	CUA Leu	CCA Pro	CAA Gln	CGA Arg	A
	CUG Leu	CCG Pro	CAG Gln	CGG Arg	G
A	AUU Ile	ACU Thr	AAU Asn	AGU Ser	U
	AUC Ile	ACC Thr	AAC Asn	AGC Ser	C
	AUA Ile	ACA Thr	AAA Lys	AGA Arg	A
	AUG Met start	ACG Thr	AAG Lys	AGG Arg	G
G	GUU Val	GCU Ala	GAU Asp	GGU Gly	U
	GUC Val	GCC Ala	GAC Asp	GGC Gly	C
	GUA Val	GCA Ala	GAA Glu	GGA Gly	A
	GUG Val	GCG Ala	GAG Glu	GGG Gly	G

Amino acids and their codons

Amino acid	Letter	3-letter	Codons	Which codons
Alanine	A	Ala	4	GCU GCC GCA GCG
Arginine	R	Arg	6	CGU CGC CGA CGG AGA AGG
Asparagine	N	Asn	2	AAU AAC
Aspartic acid	D	Asp	2	GAU GAC
Cysteine	C	Cys	2	UGU UGC
Glutamic acid	E	Glu	2	GAA GAG
Glutamine	Q	Gln	2	CAA CAG
Glycine	G	Gly	4	GGU GGC GGA GGG
Histidine	H	His	2	CAU CAC
Isoleucine	I	Ile	3	AUU AUC AUA
Leucine	L	Leu	6	UUA UUG CUU CUC CUA CUG
Lysine	K	Lys	2	AAA AAG
Methionine	M	Met	1	AUG
Phenylalanine	F	Phe	2	UUU UUC
Proline	P	Pro	4	CCU CCC CCA CCG
Serine	S	Ser	6	UCU UCC UCA UCG AGU AGC
Threonine	T	Thr	4	ACU ACC ACA ACG
Tryptophan	W	Trp	1	UGG
Tyrosine	Y	Tyr	2	UAU UAC
Valine	V	Val	4	GUU GUC GUA GUG
Stop	-	Ter	3	UAA UAG UGA

How to read the codon chart

A codon is a group of three bases in messenger RNA that specifies one amino acid or a signal to stop. The standard genetic code has 64 codons: 61 specify the 20 amino acids and three (UAA, UAG, UGA) are stop codons (NCBI Taxonomy, The Genetic Codes, table 1; Wikipedia). Most amino acids have more than one codon, which is why the code is called degenerate. Read the chart by first base (left), second base (column) and third base (right). DNA letters show the coding strand, with T in place of U.

Worked example. AUG codes for Methionine and is the usual start codon; NCBI's standard code also allows UUG and CUG as alternative initiation codons. UGG is the only codon for Tryptophan. Leucine has 6 codons (UUA, UUG, CUU, CUC, CUA, CUG), so the lookup for "Leu" lists all of them. To translate a whole pasted sequence, use the DNA translator linked on this page.

Frequently asked questions

How many codons are there?

There are 64 possible three-base codons. In the standard code, 61 specify amino acids and 3 are stop codons: UAA, UAG and UGA.

What is the start codon?

AUG, which codes for methionine. The NCBI standard code also lists UUG and CUG as alternative initiation codons in some cases.

Why do some amino acids have several codons?

The code is degenerate: leucine, serine and arginine each have six codons, while methionine and tryptophan have one each.

What is the difference between the DNA and RNA codon table?

Only the letters: RNA uses U where DNA uses T. The tool can show either, and the DNA letters here are for the coding strand.

Does this cover mitochondrial or other genetic codes?

No. This is the Standard Code (NCBI table 1). NCBI lists other codes, such as the vertebrate mitochondrial code, that differ for a few codons.

Sources

Checked8 October 2026

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Teaching model, not advice

Reference for the standard nuclear genetic code. Other organisms and organelles can use variant codes.