Talent departments plan for future staffing requirements based on the forecasting of positions the company must fill to meet future needs. Forecasts are based on the estimated demands for products and services. Revenues are determined first and staffing plans developed accordingly.
Forecasting hiring numbers is a pretty complex process, but you’ve gotta start somewhere. A great place to start is at your company’s goals—for instance, revenue. The maths isn’t that difficult, but it might remind you of the story problems you did back in high school. If the company wants to make X by a certain date and each salesperson typically brings in Y, how many more salespeople will you need in order to make the goal?
A skills gap analysis will provide a general idea of how many new hires you’ll need to cover the gaps you have, but there are many other ways to predict hiring needs. You can use quantitative methods to forecast future hires into your recruitment plan. E.g. companies may set daily sales targets to hit their revenue goals. They can use productivity metrics to find out if the current number of employees can achieve the goals. If not, they can calculate how many more people they need to hire.