Barley grain is a commonly fed energy feedstuff for grower-finisher pigs in western Canada. However, its feeding value for weaned pigs is poorly characterized, especially by modern feed formulation method using NE values and standardized ileal digestible (SID) AA coefficients for feedstuffs. Formulating lower nutrient dense diets may reduce feed cost, provided weaned pigs can maintain growth performance by increasing ADFI to meet requirements. To compare the feeding value of wheat- and barley-based diets with high- or low- nutrient density, 4 diets based on 64% wheat or 68% barley grain providing either 2.4 or 2.3 Mcal NE/kg were fed in a 2 × 2 factorial arrangement to 208 weaned pigs (9.0 kg) housed in 13 pens per diet. Diets were formulated to 4.5 g SID Lys/Mcal NE and were fed for 21 d. Feed added, remaining, and pig BW were measured weekly to calculate pen ADFI, ADG, and G:F. Freshly-voided feces were collected on d 19 and 20 to measure diet apparent total-tract digestibility (ATTD) of DM, GE, and CP and diet DE values. No interactions between cereal source and nutrient density were observed. Compared with wheat-based diets, feeding barley-based diets reduced (P < 0.01) the ATTD of DM, GE, and CP by 2.7, 3.0, and 4.4%, respectively, and reduced (P < 0.01) measured diet DE value by 0.05 Mcal/kg. Compared with high-nutrient density diets, feeding low-nutrient density diets reduced (P < 0.01) ATTD of DM, GE, and CP by 2.6, 1.8, and 2.3%, respectively, while measured diet DE value was not affected. Overall, feeding barley-based diets increased (P < 0.01) ADG by 41 g and G:F by 0.04 g:g compared with feeding wheat-based diets, but ADFI was not affected. Diet nutrient density did not affect ADFI, ADG, or G:F. In conclusion, feeding barley grain instead of wheat as cereal energy source for weaned pigs may increase growth performance. Growth performance of weaned pigs was not affected by reducing dietary NE by 0.1 Mcal/kg when SID Lys/NE was maintained. Feeding barley- instead of wheat-based diets provided advantages for the feeding of weaned pigs.