Two approaches are detailed for the determination of forming limit diagrams (FLD). The first one is experimental:​ a correlation technique has been developed for the displacement field measurement on a sheet. The second approach is theoretical:​ a necking criterion based on the load-instability and plane strain localization assumptions is proposed. It includes the possibility to introduce the modified Gurson–Tvergaard damage model taking account Hill's or Barlat and Lian's anisotropy. The criterion is written in an intrinsic form and is applicable to linear strain paths as well as to non-linear strain paths. Finally, the FLD for three aluminum sheets and a mild-steel sheet obtained by experimental and theoretical ways are compared.