The calculation is a comparison of entered limits
Indoor count = indoor area divided by indoor allowance, rounded down. Outdoor count uses the same arithmetic. The result takes the smallest entered count, including a local limit if provided. It does not certify the welfare, carrying capacity or legal suitability of the flock.
Why an acre alone is not enough
Area occupied by the house, paths, wet ground, shade, equipment and service access may not be usable animal space. Housing, species, age, predator protection, drainage, ventilation, biosecurity and daily care can constrain the flock before the land area does. Choose allowance inputs with appropriate local Extension, veterinary and authority guidance.
A worked example with invented inputs
If you enter 60 sq ft indoors at an assumed 5 sq ft per bird, the indoor arithmetic gives 12. If you enter 150 sq ft outdoors at an assumed 15 sq ft per bird, the outdoor arithmetic gives 10. An entered local limit of 6 makes the comparison result 6. The 5 and 15 sq ft assumptions teach the calculation; they are not universal chicken standards.
Plan the complete backyard flock