Particle size determination by sieving is a standard method used to estimate the geometric mean (dgw) and geometric standard deviation (Sgw) of feedstuffs. However, the method allows for variation in time of sieving, sieve agitator setup, and the use of dispersing agent (fumed silica). The objectives of this experiment were to determine which method of particle size analysis best estimates the particle size of cereal grain and assess analytical variation within each method. Treatments were arranged in a 4 × 3 × 3 × 2 factorial design with 4 sieving methods: (1) 10 min with sieve agitators (10A), (2) 15 min with no sieve agitators (15N), (3) 15 min with sieve agitators (15A), or (4) 15 min with sieve agitators and a dispersing agent (15AS), 3 cereal grains (corn, wheat, or sorghum), 3 grinds (coarse, medium, or fine), and 2 mills (hammermill or roller mill). Mill parameters were adjusted to achieve 3 grinds with coarse being the largest and fine being the smallest. Samples were analyzed for particle size according to ASAE S319.3. Data were analyzed using GLIMMIX procedure of SAS with 4 replicates per treatment. Interactions were removed from the model if P > 0.05. The main effects of method, grain, grind size, and grind method all differed (P < 0.01) for both dgw and Sgw. All methods were significantly different from one another (P < 0.05; 587, 615, 576, and 541 for dgw and 2.23, 2.09, 2.27, and 2.63 for Sgw for 10A, 15N, 15A, and 15AS, respectively). All grains differed from one another, with corn having the smallest dgw and Sgw (P < 0.05; 537 and 2.28, 550 and 2.34, 652 and 2.31, respectively for corn, sorghum, and wheat dgw and Sgw). Hammermill ground grain had a smaller dgw and larger Sgw than roller mill ground grain (P < 0.05; 415 and 2.62 vs. 744 and 1.99, respectively). As expected, varying grind size resulted in different dgw (P < 0.05), but Sgw was also affected as the coarse and medium grinds had greater Sgw than the fine grind (2.36 and 2.35 vs. 2.23, respectively). In summary, the particle size analysis method of 15AS provided the lowest dgw and highest Sgw, suggesting that all particles had reached their appropriate spot within the sieve stack and thus was the most accurate of the tested methods.