A: A prime cost sum (PC or PC sum) is an allowance, usually calculated by the cost consultant, for the supply of work or materials to be provided by a contractor or supplier that will be nominated by the client (that is, a supplier that is selected by the client to carry out an element of the works and imposed on the main contractor after the main contractor has been appointed).

The allowance is exclusive of any profit mark up or attendance (such as material handling, scaffolding and rubbish clearance, etc.) by the main contractor.