In order to accurately design and analyze demand controlled volume ventilation systems, theoccupancy level in the room must be known. The occupancy level corresponds to the length of time people occupy a room. Since there is a lack of data for occupancy levels in regards to offices, this study reports on measured occupancy levels for three cell offices in Sweden. The same occupancy sensors were used as those found on the ventilation systems. The results showed that the occupancy level for an office was as low as 11.2%. This will influence the benefits from demand controlled volume ventilation systems. Estimated energy savings of almost two thirds was found when compared to constant volume systems.