Abstract Background and Aims The pericarp weight comprises <17 % of wheat grain weight at harvest. The pericarp supports the hydration and nutrition of both the embryo and endosperm during early grain filling. However, studies of the pericarp and its association with final grain weight have been scarce. This research studied the growth dynamics of wheat pericarp from anthesis onwards and its relationship to final grain weight under contrasting plant densities and night warming. Methods Two spring wheat cultivars contrasting in kernel weight (Bacanora and Kambara) were sown in field conditions during seasons 2012–13 and 2014–15. Both genotypes were grown under contrasting plant density (control, 370 plants m–2; and low plant density, 44 plants m–2) and night temperatures, i.e. at ambient and increased (>6 °C) temperature for short periods before and after anthesis. From anthesis onward, grains were harvested every 3 or 4 d. Grain samples were measured and the pericarp was removed with a scalpel. Whole grain and pericarp fresh and dry weight were weighed with a precision balance. At harvest, 20 grains from ten spikes were weighed and grain dimensions were measured. Key Results Fresh weight, dry matter and water content of pericarp dynamics showed a maximum between 110 and 235 °Cd. Maximum dry matter of the pericarp ranged between 4.3 and 5.7 mg, while water content achieved values of up to 12.5 mg. Maximum values and their timings were affected by the genotype, environmental condition and grain position. Final grain weight was closely associated with maximum dry matter and water content of the pericarp. Conclusions Maximum pericarp weight is a determinant of grain weight and size in wheat, which is earlier than other traits considered as key determinants of grain weight during grain filling. Better growing conditions increased maximum pericarp weight, while higher temperature negatively affected this trait.