Nutrients excreted from animals affect the nutritive value of manure as a soil amendment as well as the composition of gases emitted from manure storage facilities. There is a dearth of information, however, on how diet type in combination with dietary particle size affects nutrients deposited into manure storage facilities, and how this subsequently affects manure composition and gas emissions. To fill this knowledge gap, an animal feeding trial was performed to evaluate potential interactive effects between feed particle size and diet composition on manure characteristics and manure‐derived gaseous emissions. Forty eight finishing pigs housed in individual metabolism crates which allowed for daily collection of urine and feces were fed diets differing in fiber content and particle size, with their urine and feces collected and stored in 446 L stainless steel containers over a period of 49 d. There were no interactive effects between diet composition and feed particle size on any manure or gas emission parameter measured. In general, diets higher in fiber content increased manure nitrogen (N), carbon (C), and total volatile fatty acid (VFA) concentrations, and increased manure VFA emissions, but decreased manure ammonia emissions. Decreasing the particle size of the diet lowered manure N, C, VFA, phenolics, and indole concentrations, and decreased manure emissions of total VFA. Neither diet composition nor particle size had an impact on manure greenhouse gas emissions (GHG).