I was keeping my timesheet on google spread sheet. I was just mentioning start time and end time of particular task. My project manager asked me to add number of hours as another column.
When I search for the formula I found this link http://www.google.com/support/forum/p/Google+Docs/thread?tid=071c90492bf64b75&hl=en . In that link I found solution to my problem.
I need to keep start time in one column(ex: A4 with value 10:50:00), end time in another column(ex.B4 with value 13:42:00). I should maintain time in 24 hours format. I have another column called Hours(ex. D4 should have 2.9 hours).
The cell value for Hours column should be difference of time from B4 and A4 in terms of hours. So I used =ROUND(ABS(B4-A4) * 24, 1) formula in that cell. I got the exact number of hours I spent. Just drag the column with ‘+’ to affect the same formula for the rest of the cells in the hours column.