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Enter your values, then click Calculate result.How this calculator helps
This GC calculator counts guanine and cytosine in a DNA or RNA sequence and makes the denominator visible. Paste one plain sequence or one FASTA record, select the alphabet and decide whether unresolved N positions belong in the denominator. The result includes individual base counts, known positions and GC skew. It never assigns an unknown base a guessed identity. That distinction helps compare a resolved sequence with a partially assembled record without presenting missing information as measured composition.
How to use it
- 1
Read the input basis and the documented limits before entering values.
- 2
Enter the required values in the labeled units and choose the applicable mode.
- 3
Click Calculate result to evaluate the supplied inputs.
- 4
Keep the selected model and assumptions with your result; edited inputs require another calculation.
Formula and methodology
Known-base GC% = 100 × (G + C)/(A + C + G + T or U). All-position resolved GC% = 100 × (G + C)/total positions. GC skew = (G − C)/(G + C).
The calculator applies the displayed arithmetic to the values entered on this device. It does not silently load a local tax rate, currency conversion or commercial assumption.
Worked calculation example
ACGTNN has four known bases and six total positions. G+C is two: known-base GC content is 50%, while resolved G+C across all positions is 33.333333%. GC skew is zero.
How to interpret your result
GC percentage describes nucleotide composition on the selected denominator. The known-base result is conditional on resolved bases; the all-position result is a resolved lower bound when N is present. GC skew is a separate imbalance statistic, not a percentage or a diagnosis. Results follow the last submitted sequence, alphabet and denominator. A different denominator can change the percentage without changing any observed base counts.
For different inputs or formulas, use Molarity Calculator; Percent Calculator; Basic Calculator.
Related questions this calculator covers
- gc calculator
Scenario comparison
| Scenario | What it shows |
|---|---|
| GGCC: four known positions, 100% GC and zero skew. | |
| AATT: zero GC and undefined GC skew because G+C is zero. | |
| NNNN: known-base percentage is undefined; all-position resolved GC is zero. |
Common mistakes to avoid
- Do not treat unresolved N as a known low-GC base in a reported complete composition.
- A header containing letters is descriptive text, not sequence content; multiple FASTA records need separate handling.
- GC skew and GC content have different denominators and should retain their statistic names.
Verify each base count independently, then sum G and C. Calculate both denominators explicitly and compare the displayed percentages. Repeating a resolved sequence twice should double its counts while leaving GC content and skew unchanged. Reordering bases should also leave these whole-record statistics unchanged; the tool is not performing a position-dependent analysis.
Authoritative reference. IIT Guwahati Aptabase provides a nucleotide GC-content calculation. The ambiguity and denominator policies on this page are explicitly implemented by SolvePilot.What can affect the result?
Choose DNA or RNA before counting
DNA mode accepts A, C, G, T and N. RNA mode substitutes U for T. Lowercase letters are converted to uppercase, and whitespace between bases is removed. The selection prevents a mixed T/U record from passing silently. Other IUPAC ambiguity codes are deliberately unsupported rather than being counted as if they had a single identity. Correct the sequence or use an appropriate specialized ambiguity-aware program if your record contains R, Y or other codes.
What the known-base denominator means
Excluding N answers a conditional question: what fraction of the bases that have known identities are G or C? It does not reveal the identities of unresolved positions. If the missing positions have different composition from resolved positions, the conditional percentage may differ from the eventual complete-sequence percentage. Keep the selected denominator with your result whenever comparing records, reporting quality information or explaining why two applications produced different values for the same pasted text.
All-position GC is an observed lower bound
Including N in the denominator counts only resolved G and C in the numerator. For a sequence containing unresolved positions, that fraction is a lower bound on the complete sequence GC fraction. Every N could later resolve to A/T or to G/C. The tool does not assume a random equal distribution. An all-N sequence therefore gives zero resolved G+C among all positions, while its known-base GC percentage remains undefined because no known-base denominator exists.
Plain sequence and one FASTA record
A FASTA header begins with a greater-than sign and must be the first line. It is ignored for counting, so digits or descriptive words in the header do not become sequence bases. Only one record is supported. Pasting several records would otherwise make it unclear whether to concatenate them or average individual percentages. Sequence spaces and line breaks can be removed safely within the single record. Unsupported punctuation in the sequence is rejected instead of silently discarded.
Read counts before trusting a percentage
The percentage is only as reliable as the intended record. Compare total positions with the length expected from your source. Check N count and whether T or U appears on the correct alphabet basis. A surprising result can come from a truncated copy, an extra sequence line or the wrong record. Counts are integers and should reconcile exactly: known bases plus unresolved N equals total positions, and the sum of every displayed base count equals that same total.
GC skew answers a different question
GC percentage combines G and C, while skew compares their relative imbalance. The expression G minus C divided by G plus C ranges from minus one to plus one whenever at least one G or C is present. A balanced sequence has zero skew even when GC content is very high or low. A sequence containing only A and T has no G+C denominator, so skew is undefined. Do not confuse this whole-record skew with a sliding-window analysis.
Boundaries of a composition calculation
The browser accepts up to one hundred thousand sequence positions and two hundred thousand pasted characters. It does not identify species, calculate melting temperature, inspect primers, validate laboratory samples or interpret genetic disease. Such tasks require additional models and evidence. Short sequences can show extreme percentages simply because each base is a large fraction of the total. No uncertainty interval or experimental quality score is invented from the sequence string alone.
Privacy and browser processing
Values entered on this page are processed in the current browser session. SolvePilot does not require an account and does not receive the values entered into the calculator. Refreshing or closing the page clears the working values unless the browser itself restores a previous session. Avoid entering identifying or account information because the calculation needs summary values only.
Accuracy and verification
Accuracy depends first on input quality. Confirm definitions, scales, dates and source information before entering a value. Keep an independent record of any result used for planning because this page does not create an official statement or retain a calculation history.
Limits of this estimate
The browser accepts up to one hundred thousand sequence positions and two hundred thousand pasted characters. It does not identify species, calculate melting temperature, inspect primers, validate laboratory samples or interpret genetic disease. Such tasks require additional models and evidence. Short sequences can show extreme percentages simply because each base is a large fraction of the total. No uncertainty interval or experimental quality score is invented from the sequence string alone.
Sources and review information
Frequently asked questions
What does a GC calculator calculate?＋
It counts G and C and divides by the disclosed sequence denominator. This page supports DNA and RNA, with an explicit policy for unresolved N bases rather than a hidden assumption.
Can I paste a FASTA sequence?＋
Yes, one record with its header on the first line. The header is excluded, while sequence whitespace is removed. Multiple records must be calculated separately.
Why do known-base and all-position results differ?＋
N is excluded from the first denominator and included in the second. The all-position result counts only resolved G+C and is a lower bound when N is present.
Does GC content give melting temperature?＋
No. Melting-temperature models depend on factors such as sequence, length, salt conditions and concentration. A composition percentage alone is not that calculation.
How can I check the count by hand?＋
For ACGTNN, count one A, C, G and T and two N. The resolved fraction is two out of six; the known-base fraction is two out of four.