The calculator multiplies your headcount by a typical range of usable square feet per person, based on how you work: about 125–175 SF per person for open and collaborative teams, 175–250 SF for a balanced mix, and 250–350 SF for mostly private offices.
It then adds the load factor to convert usable square feet into rentable square feet, since that's how space is quoted and priced. For example, 25 people in a balanced layout works out to roughly 4,375–6,250 usable SF, or about 5,031–7,188 RSF at a 15% load factor.
Use it as a starting point. Conference rooms, storage, a reception area, hybrid schedules and planned growth can all move the number in either direction.
Should I plan for growth?
Usually, yes. Moving is expensive, so it often makes sense to plan for where your headcount will be partway through the lease. Expansion rights, rights of first refusal and sublease rights are ways to add flexibility without paying for empty space on day one.
How do hybrid schedules change the math?
If people aren't in every day, you may not need a desk for everyone. Many teams plan around peak days instead of total headcount, then add more meeting and collaboration space.
Why does the result show two numbers?
Usable SF is the space your team occupies. Rentable SF adds your share of common areas, and it's the number rent is based on. You'll want both when you compare spaces.