You'd specify the substrate, over which you've deposited the graphine layer and its crystalline structure. Therefore the strain is calculated from interatomic distance mismatch (ag-as)/as
Graphene is consisting of a single layer of atoms arranged in a two-dimensional lattice.Therefore Applying This Term (compressive stress) for it, is Meaningless.
Wang, M., Huang, M., Luo, D. et al. Single-crystal, large-area, fold-free monolayer graphene. Nature 596, 519–524 (2021). https://doi.org/10.1038/s41586-021-03753-3
there are some related references in this article which are helpful for the calculation of compressive strain in a graphene film.