Th e study evaluates the associations of the farm herd size (HERD), the milk yield (MY, kg/cow per year), and cows per worker (CW) with the production, reproduction, and economic traits in 60 commercial dairy herds (34 633 cows) in the Czech Republic. Each parameter was split into 3 groups. Th e largest herds (≥ 750 cows) had the highest profi tability of costs without subsidies (−3.8 ± 4.3%), the lowest cost for roughages (1.2 CZK/L milk), and the lowest cost for breeding operations (0.17 CZK/L milk), but the highest costs for the cereal grains and concentrates (2.4 CZK/L milk). Herds with the lowest MY (≤ 7 499) had the lowest profi tability of costs without subsidies (−15.8 ± 3.93%), the highest total costs (9.27 CZK/L milk), the highest labour costs (1.6 CZK/L milk), and the highest cow depreciation costs (0.97 CZK/L milk). Herds with the lowest CW (≤ 39) had the highest mean labour costs (1.51 CZK/L milk) and the highest costs for breeding operations (0.22 CZK/L milk). Herds with the highest CW (≥ 60) and the lowest CW (≤ 39) also diff ered in the total feed costs (4.1 vs. 3.73 CZK/L milk) and the costs of cereals and concentrates (2.34 vs. 1.96 CZK/L milk). Th e increasing herd size tended to be accompanied by higher milk yields and the overall effi ciency.