Objective: To test the validity of a sitting pad (SP) to measure desk based sitting time and transitions, against camera derived direct observation; and to compare the data with those from inclinometers in the ActivPAL3 (AP) and ActiGraph GT3X+(AG). Methods: Australian employees (n=13; 9 women; mean age 30±6.5 years) were provided with a SP, AG and AP in 2011. A camera recorded chair based transitions during a prescribed and a free living protocol. Mean sitting time and transitions were calculated for each device and intra-class correlations (ICCs) and mean differences between (a) the SP and the camera and (b) the AP, AG and camera, were compared. Results: During the prescribed protocol, the smallest mean differences compared with the camera were for the SP; sitting time 0.30±0.21 minutes, transitions-0.46±0.78. During free living, both the SP and AP (set to record events greater than 3seconds) showed excellent levels of agreement with the camera for sitting time (0.999 and 0.990 respectively) and transitions (0.997 and 0.928 respectively). Agreement between the camera and the AG was poor for both sitting time and transitions (0.257 and 0.033 respectively). Conclusions: The SP is a highly accurate measure of desk based sitting time and transitions and provides novel measurement and intervention opportunities for research into occupational sitting.