Headcount planning translates an hours shortage into a hiring requirement. Start with unfilled demand, then deduct current qualified availability once. A person with several skills can't supply the same free hour to two concurrent roles. Match the requirement before treating general bench time as usable supply.
Desk Staffing reports additional full-time equivalents using a forty-hour planning convention. It takes the peak weekly shortage after qualified supply, divides by forty and rounds up to a whole position. Rounding down would leave part of the requirement uncovered. This convention is a training assumption, not a universal employment contract. A part-time hire or a phased start could produce a different plan and should be modeled explicitly. Weighted demand can support a risk discussion, but an approved hiring request should state which demand basis and dates justify its headcount.