Read-Length Coverage - Physics for Biophysics Step by Step

Sequencing coverage is a counting ratio over a simplified genome track. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

Coverage is total read bases over genome bases

Coverage equals read count times read length divided by genome length.

\text{coverage}=\frac{\text{reads}\cdot\text{read length}}{\text{genome length}}

The first toy case gives exact coverage

Read count 10 times read length 100 over genome length 1000 gives coverage 1 x.

\frac{10\cdot 100}{1000}=1

More reads increase coverage

With read count 20 and the same lengths, coverage becomes 2 x.

\frac{20\cdot 100}{1000}=2

Coverage follows read count in exact rows

Read length and genome length stay fixed. Changing the read count changes only the numerator.

\begin{array}{c|c}\text{reads}&\text{coverage}\\5&\frac{1}{2}\\10&1\\20&2\end{array}