Codon Chart
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GENETIC CODE REFERENCE

Codon chart

64 codons. RNA, DNA and printable charts.

Read 5′ → 3′Download PDF
Standard code · Options

Exports use the selected code. CSV includes all 64 codons in RNA and DNA, with listed initiation and stop flags.

Genetic code reference

How to read this chart
Standard Code RNA codon chart. First base at left, second base across the top, third base at right. Read 5′ to 3′.
1stbaseSecond base3rdbase
UCAG
UU
C
A
G
CU
C
A
G
AU
C
A
G
GU
C
A
G
NonpolarPolarAcidicBasicStopStart initiation codon
3 listed initiation codons

Listed initiation codons · table 1

These are possible starts in NCBI table 1, not a prediction that a sequence starts there. The amino acids below are their internal assignments.

UUGInternal: LeuCUGInternal: LeuAUGInternal: Met

A chosen initiator is translated as methionine. Ordinary codon lookup keeps the internal assignment; initiation needs the appropriate organism and sequence context.

Standard code (NCBI table 1). Start-codon use depends on the organism and sequence context.

Read AUG: methionine

Practice
  1. 1. Left sideA
  2. 2. Top columnU
  3. 3. Right sideG

Find the first-base group, the second-base column and the third-base row. Their intersection is your codon.

Read 5′ to 3′. Use the mRNA codon, not its tRNA anticodon.

Practice reading a codon chartEight codons, two short sequences and an explained answer key.

Use the standard genetic code (NCBI table 1) for every question, independently of the chart options above. These are illustrative sequences.

Worksheet PDFAnswer key PDF

Read 5′ to 3′. For questions 1–8, use an amino acid’s name, three-letter or one-letter code, or “Stop”. For 9–10, start at the first base and give the peptide in one-letter codes; stop at the first stop codon and omit it.

Show answers and explanations
  1. Tryptophan (Trp, W)

    First base U, second G, third G: Tryptophan (Trp, W).

  2. Lysine (Lys, K)

    First base A, second A, third A: Lysine (Lys, K).

  3. Aspartic acid (Asp, D)

    First base G, second A, third C: Aspartic acid (Asp, D).

  4. Serine (Ser, S)

    First base U, second C, third U: Serine (Ser, S).

  5. Stop

    First base U, second A, third G: Stop.

  6. Methionine (Met, M)

    First base A, second U, third G: Methionine (Met, M).

  7. Proline (Pro, P)

    First base C, second C, third A: Proline (Pro, P).

  8. Valine (Val, V)

    First base G, second U, third U: Valine (Val, V).

  9. MAWKD

    AUG = Met; GCC = Ala; UGG = Trp; AAA = Lys; GAC = Asp; UAA = Stop. The stop adds no amino acid.

  10. MF

    AUG = Met; UUU = Phe; UGA = Stop. The stop adds no amino acid. Do not translate GGU after that stop.

Assignments follow NCBI’s standard code. A start codon alone does not establish where a real gene begins. More about starts and stops.

KEEP A REFERENCE

Printable RNA and DNA codon charts

Download a one-page PDF, an editable SVG or a high-resolution PNG. These sheets use the standard genetic code (NCBI table 1). For another code, use the chart’s download controls above.

Standard-code RNA codon table, with all 64 codons and their amino-acid or stop assignments

RNA codon table

PDF — RNA codon tableSVG — RNA codon tablePNG — RNA codon table
Standard-code DNA codon table, with all 64 codons and their amino-acid or stop assignments

DNA codon table

PDF — DNA codon tableSVG — DNA codon tablePNG — DNA codon table
Black-and-white RNA codon chart: all 64 standard-code assignments, with white cells, outlined rows and first, second and third base labels

RNA codon chart — black and white

PDF — RNA codon chart — black and whiteSVG — RNA codon chart — black and whitePNG — RNA codon chart — black and white
Black-and-white coding-DNA codon chart: all 64 standard-code assignments, with white cells, outlined rows and first, second and third base labels

DNA codon chart — black and white

PDF — DNA codon chart — black and whiteSVG — DNA codon chart — black and whitePNG — DNA codon chart — black and white

Download all 64 codon assignments (CSV) for a spreadsheet: coding DNA, RNA, one-letter and three-letter symbols, and full amino-acid or stop names. The CSV always uses NCBI table 1 and reads both alphabets 5′ to 3′.

Assignments from NCBI’s genetic-code tables. Read the sequence 5′ to 3′. Switching to DNA letters replaces U with T; it does not complement a strand.

CODING STRAND

DNA codon table

The same 64 codons in DNA letters, with T in place of U. It reads the coding strand 5′ to 3′, the strand with the mRNA’s sequence: ATG is the start codon, and TAA, TAG and TGA are the stops.

Standard genetic code in DNA letters (NCBI table 1). First base at left, second base across the top; each cell is a codon and its amino acid.
First baseTCAG
TTTT PheTCT SerTAT TyrTGT Cys
TTC PheTCC SerTAC TyrTGC Cys
TTA LeuTCA SerTAA StopTGA Stop
TTG LeuTCG SerTAG StopTGG Trp
CCTT LeuCCT ProCAT HisCGT Arg
CTC LeuCCC ProCAC HisCGC Arg
CTA LeuCCA ProCAA GlnCGA Arg
CTG LeuCCG ProCAG GlnCGG Arg
AATT IleACT ThrAAT AsnAGT Ser
ATC IleACC ThrAAC AsnAGC Ser
ATA IleACA ThrAAA LysAGA Arg
ATG Met startACG ThrAAG LysAGG Arg
GGTT ValGCT AlaGAT AspGGT Gly
GTC ValGCC AlaGAC AspGGC Gly
GTA ValGCA AlaGAA GluGGA Gly
GTG ValGCG AlaGAG GluGGG Gly

First base at left, second base across the top, third base down each group. Assignments from NCBI table 1, the standard code.

BY AMINO ACID

Codons for each amino acid

The same 64 codons grouped by what they code for: each amino acid’s full name, its three- and one-letter codes, and every codon that specifies it, in RNA and in DNA letters. AUG, methionine’s only codon, is also the start codon.

Standard genetic code by amino acid (NCBI table 1): name, codes, RNA codons and DNA codons.
Amino acidCodesRNA codonsDNA codons
AlanineAla · AGCU GCC GCA GCGGCT GCC GCA GCG
ArginineArg · RCGU CGC CGA CGG AGA AGGCGT CGC CGA CGG AGA AGG
AsparagineAsn · NAAU AACAAT AAC
Aspartic acidAsp · DGAU GACGAT GAC
CysteineCys · CUGU UGCTGT TGC
Glutamic acidGlu · EGAA GAGGAA GAG
GlutamineGln · QCAA CAGCAA CAG
GlycineGly · GGGU GGC GGA GGGGGT GGC GGA GGG
HistidineHis · HCAU CACCAT CAC
IsoleucineIle · IAUU AUC AUAATT ATC ATA
LeucineLeu · LUUA UUG CUU CUC CUA CUGTTA TTG CTT CTC CTA CTG
LysineLys · KAAA AAGAAA AAG
MethionineMet · MAUGATG
PhenylalaninePhe · FUUU UUCTTT TTC
ProlinePro · PCCU CCC CCA CCGCCT CCC CCA CCG
SerineSer · SUCU UCC UCA UCG AGU AGCTCT TCC TCA TCG AGT AGC
ThreonineThr · TACU ACC ACA ACGACT ACC ACA ACG
TryptophanTrp · WUGGTGG
TyrosineTyr · YUAU UACTAT TAC
ValineVal · VGUU GUC GUA GUGGTT GTC GTA GTG
Stop—UAA UAG UGATAA TAG TGA

Assignments from NCBI table 1, the standard code. Each amino acid’s structure, charge and properties are on the amino acid chart.

How to read a codon chart

A codon is a group of three nucleotides read in the 5′ to 3′ direction. In an RNA codon chart the bases are U, C, A and G. DNA uses T in place of U. Find the first base at the left, the second base across the top, and the third base at the right. Their intersection gives the amino acid. For example, AUG encodes methionine in the standard code and is marked Start in the chart, while UUU encodes phenylalanine. Selecting a codon shows its full amino-acid name and abbreviations beside the chart, with its exact Watson–Crick anticodon pairing when an amino-acid assignment applies.

Use the search above the chart for an immediate answer: UGG shows tryptophan, Leu lists leucine’s codons, and GCN matches four alanine codons. Search accepts RNA or DNA letters.

The guided lookup follows the selected codon through the three table axes. Try ten practice questions, check your answers and explanations, or download the RNA or coding-DNA worksheet and its answer key.

Start and stop codons

AUG (ATG in DNA) is the start codon. Translation begins there with methionine, formylmethionine in bacteria. UAA, UAG and UGA (TAA, TAG and TGA in DNA) are the three stop codons, historically named ochre, amber and opal. No tRNA reads them: a release factor ends translation instead. The other 61 codons specify the 20 amino acids, so most amino acids have several codons. Leucine, serine and arginine have six each, while methionine and tryptophan have one. That redundancy does not mean every base substitution leaves the protein unchanged. Explore all nine one-base changes to a codon to see which preserve its amino-acid assignment, change it or introduce a stop.

Some organisms also start at other codons, such as GUG and UUG in bacteria (NCBI table 11). A start codon in a sequence is not automatically where a protein begins; the genetic-code guide explains when one is used. The bases around it matter: check a eukaryotic start codon with the Kozak sequence checker and a bacterial one with the Shine-Dalgarno sequence finder.

RNA and DNA codons

Use an RNA chart for an mRNA codon. A DNA chart gives the corresponding coding-strand triplet, with T in place of U. Both are read 5′ to 3′. Changing the alphabet does not turn a template strand into a coding strand. The DNA codon table lists all 64 in DNA letters, and the RNA menu above the chart switches the chart itself to DNA. To go from an amino acid to its codons, use the codons for each amino acid table below it. To turn a whole strand into mRNA and amino acids, use DNA to mRNA.

RNA codon Coding DNA Standard-code assignment
AUG ATG Methionine (Met, M)
UGG TGG Tryptophan (Trp, W)
UAA TAA Stop
UAG TAG Stop
UGA TGA Stop

If your input is the template strand, check the coding- and template-strand example before using a codon chart. For start signals and exceptions, read how start and stop codons are interpreted. These assignments follow NCBI table 1; another table can change them.

Choose the code for your sequence

The default is NCBI translation table 1, the standard code. Mitochondria and some organisms use different assignments. Open Options beside the download button (the slider icon on phones) and select another table before interpreting a sequence from one of those systems. The chart follows the NCBI genetic-code tables, including context-dependent assignments. A codon listed as a possible start is not automatically an initiation site in a real sequence.

A genetic-code chart tells you which amino acid a codon specifies. For how often a host uses each codon, compare the human, E. coli and yeast codon usage tables, with all 64 codons and downloadable counts from the named reference annotations.

Switch to the codon wheel for a center-outward view or the amino acid chart to compare names and abbreviations. To translate an entire sequence, use DNA to protein; it lets you inspect all six reading frames.

The printable reference sheets are ready-made RNA and DNA versions of the standard code. Each has permanent PDF, SVG and PNG links, so you can download a one-page reference without configuring the tool or enabling JavaScript. The table and wheel show the same 64 assignments; choose the layout you find easier to follow.

For black-and-white printing, choose the RNA or DNA chart with white cells and outlined rows. All 64 codons, amino-acid abbreviations and the three base axes remain labeled; there is no color key to interpret. Each PDF fits on one A4 page. These sheets always use NCBI table 1, including when another genetic code is selected above.

In Options, Download SVG creates a vector chart that stays sharp when resized. Print uses a simplified page layout; your browser can also save that page as a PDF. SVG and PNG exports visibly label the selected RNA or DNA alphabet, full genetic-code name and NCBI table number. Code CSV saves all 64 codons of the selected table in both RNA and DNA, with internal assignments, listed initiation and stop flags, and source details. Search and display choices never shorten this file. Color groups make the chart easier to scan, while text labels keep every assignment readable without relying on color.

Inspect ambiguous codons and code differences

Type three IUPAC bases into the codon inspector to expand an ambiguous triplet. For example, GCN represents four codons that all encode alanine in the standard code. For TAN, TAA and TAG are stops while TAC and TAT encode tyrosine. The inspector lists both possible assignments instead of selecting one. The ambiguity examples in the genetic-code guide explain when a triplet can resolve. Context-dependent termination also remains unresolved.

For a nonstandard genetic code, marked codons and the differences panel identify internal assignments that differ from table 1. The panel also lists every possible initiation codon in the selected table, shows its internal amino-acid assignment, and compares the start list with table 1. Initiation markers remain separate from the count of changed internal assignments. Open Codons & context to see the selected codon's family and assignment notes. Ambiguous and context-dependent assignments open this explanation automatically. Download SVG for an editable vector reference, or PNG for a 2,400-pixel image; the amino-acid page exports its own amino-acid table.