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Seven dairy farms were monitored during bunker silo filling with chopped grass and legume forage (herbage) in first or second cut. The average harvest rate on each farm ranged from 18 to 30 t/h (6 to 11 t dry matter/h) with moisture content between 55 and 68%. The particle size of chopped forage averaged 15 mm and ranged from 11 to 18 mm. The smallest bunker silo was 4.9 m wide by 21.3 m deep by 3.05 m high (theoretical volume of 318 m); the largest silo was eight times bigger (15.2 m by 46.0 m by 3.7 m or 2587 m). Farms used packing tractors weighing between 5,200 and 10,000 kg. The fraction of time dedicated to compaction varied between 0.20 and 1.00 h/h. Four out of seven farms used the packing tractor more than 90% of the time for compaction, thereby minimizing idle time and circulation outside the bunker area. A grid of 24 holes was cored in each bunker at two depths (0-180 mm and 180-360 mm from the face) to provide 48 samples per cross-section. Density was expressed on a dry matter (DM) basis. For individual samples, density ranged between 61 and 470 kg DM/m with an average of 241 kg DM/m. Density at the face was on average 15% lower than density in-depth (180-360 mm from face). Samples taken at 0.5 m from the floor were always denser than samples taken at 0.5 m from the top, by an average of 58%. Samples at the centre were denser than samples taken near the wall by an average of 9%. The average indepth density from 13 bunker cross-sections ranged from 206 to 354 kg DM/m. Average in-depth density was highly and positively correlated with a compaction index, proportional to tractor mass and packing time, and inversely proportional to harvest rate. It was negatively correlated with moisture content. Mean particle length and silage height did not have a significant effect on average in-depth density.