Singularity categories of gentle algebras

We determine the singularity category of an arbitrary finite dimensional gentle algebra $\mathrm{\Lambda }$. It is a finite product of $n$-cluster categories of type ${\mathbb{A}}_1$. Equivalently, it may be described as the stable module category of a selfinjective gentle algebra. If $\mathrm{\Lambda }$ is a Jacobian algebra arising from a triangulation $\text{ct}$ of an unpunctured marked Riemann surface, then the number of factors equals the number of inner triangles of $\text{ct}$.