A range of Ni–Mn–Ga alloy compositions close to the stoichiometric Heusler composition, ${\mathrm{Ni}}_2\mathrm{MnGa},$ has been reported to show field-induced strains of several percent. Such observations, and the magnitude of the strain observed, depend on the values of several critical material parameters, most importantly the martensitic transformation temperature ${\mathrm{(T}}_{\mathrm{mart}}\mathrm{),}$ Curie temperature ${\mathrm{(T}}_C\mathrm{),}$ saturation magnetization ${\mathrm{(M}}_s\mathrm{),}$ strength of the magnetocrystalline anisotropy, and the details of the martensite structure. Here, data collected from a variety of sources are plotted and their variations are fit with empirical formulas to afford a better overall picture of the behavior of this system. It is found that the martensitic transformation temperature is the parameter most sensitive to the composition; saturation magnetization appears to peak sharply at 7.5 valence electrons/atom, finally the composition field over which the saturation magnetization exceeds 60 emu/g, and 300 K ${\mathrm{<T}}_{\mathrm{mart}}{\mathrm{<T}}_C,$ has been explored only at the margins.