How are N bases handled?

They are counted separately and included in the total length, but excluded from both GC and AT percentages, so a sequence with many Ns can show GC% + AT% below 100%.

How is this different from the GC content tool?

The GC content tool focuses on the GC percentage; this one gives the full per-base breakdown (A, C, G, T, N counts) plus both GC% and AT% in one view.

Base composition calculator

Count each base (A, C, G, T, N) in a DNA sequence and report length, GC% and AT%. A quick compositional profile for any sequence.

How it works

Formula

Count each of A, C, G, T and N. GC% = (G + C) ÷ length × 100; AT% = (A + T) ÷ length × 100. N bases are counted in the length but are neither GC nor AT.

Worked example

ATGCGC (6 nt): A 1, T 1, G 2, C 2, N 0. GC% = 4 ÷ 6 × 100 = 66.7%; AT% = 2 ÷ 6 × 100 = 33.3%.

When to use it

For a quick compositional summary of a sequence — checking GC/AT balance, spotting an N-rich (low-quality) stretch, or getting exact base counts before primer or probe design.

Sensible defaults

The default ATGCGC is 66.7% GC. Paste any sequence, including Ns, to profile it.

FAQ

How are N bases handled?: They are counted separately and included in the total length, but excluded from both GC and AT percentages, so a sequence with many Ns can show GC% + AT% below 100%.
How is this different from the GC content tool?: The GC content tool focuses on the GC percentage; this one gives the full per-base breakdown (A, C, G, T, N counts) plus both GC% and AT% in one view.