The polarimeter vector field for multibody decays of a spin-half baryon is introduced as a generalisation of the baryon asymmetry parameters. Using a recent amplitude analysis of the Λc+ → pK − π + decay performed at the LHCb experiment, we compute the distribution of the kinematic-dependent polarimeter vector for this process in the space of Mandelstam variables to express the polarised decay rate in a model-agnostic form. The obtained representation can facilitate polarisation measurements of the Λc+ baryon and eases inclusion of the Λc+ → pK − π + decay mode in hadronic amplitude analyses. [Figure not available: see fulltext.].