How to calculate hours for a task in MS Project?

If you want to make your planning and estimation little easier then you can add a Custom Field Column in project that will calculate the total hours for a task and group of tasks.

to achieve this start project with new plan and the basic screen that you will see is below

Now right click on Start column and add a new Field, like you see in below snapshot

Now right click on newly added column and select Customize Fields. Also notice that i selected Formula option and the other option of Sum for a group of tasks like you see below

Now click on Formula button and just enter [Duration]/60 that you see below

where, 60 is value for 1 minute i.e. 60 seconds [MS project does all calculation in seconds ]

Click ok to messages and now you will that your newly addes column shows the total hours for a task as well as for a group too. This is how the final screen looks like

But one thing i observed is when you change the timings in calendar from 7 hours a day or 8 houres or so then project changes the value of duration column but the Custom Field values remains proper.

Use the Organizer (Tools > Organizer) to copy the custom field to Global.mpt. Each new project created from that point forward will have the formula in the field.

Hope it helps someone