Build the number twice
Top down
Start from what the business needs: fixed costs, planned investment, the growth you want. That produces a revenue figure. It is a legitimate number and it carries no information whatsoever about whether it is achievable.
Bottom up
Start from capacity. How many salespeople, how many working weeks after leave and holidays, how many conversations each can genuinely hold per week, and what your conversion rates are through each stage. Multiply through. That produces a second revenue figure, and this one is grounded in arithmetic.
The gap
The two numbers will differ, often substantially. The gap is the actual planning conversation and there are only four honest responses to it: accept the lower number, hire, generate more enquiries, or improve conversion by a stated amount with a stated plan. Declaring the gap closed by assertion is a fifth option and it is the one that produces targets nobody believes.