Work out how many people a workload needs, including headroom.
Rated capacity is a ceiling, not a design point, so it is derated by the headroom percentage before dividing. The result is rounded up because you cannot deploy a fraction of a person. Sizing to rated capacity leaves nothing for peaks or failures; the spare-capacity line shows whether the rounded-up count actually buys useful work capacity.
Work Capacity
Units = ⌈demand ÷ (capacity per unit × (1 − headroom))⌉
Units = ⌈demand ÷ (capacity per unit × (1 − headroom))⌉ Rated capacity is a ceiling, not a design point, so it is derated by the headroom percentage before dividing. The result is rounded up because you cannot deploy a fraction of a person.
Sizing to rated capacity leaves nothing for peaks or failures; the spare-capacity line shows whether the rounded-up count actually buys useful work capacity.
This calculator takes 3 inputs: Hours of work to deliver per month, Productive hours per person per month, Headroom reserved for peaks. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.