Use the result as a scenario, not a black box
The calculator separates the room into three planning layers: geometry, electrical load and operating assumptions. Geometry gives you square footage and cubic volume. Fixture coverage and wattage turn the room into a connected lighting load. Your electricity rate converts that load into a monthly operating cost. The ventilation result uses the air-changes-per-hour value you enter rather than pretending one universal airflow number fits every facility.
How the math works
Floor area = length × width. Volume = area × height. Fixture count = ceiling(area ÷ fixture coverage). Monthly lighting kWh = fixture count × fixture watts ÷ 1,000 × hours/day × 30. Ventilation CFM = volume × ACH ÷ 60. Plant positions = usable canopy area ÷ square feet per plant.
A 12 × 10 × 8 foot room has 120 square feet of floor area and 960 cubic feet of volume. With 16-square-foot fixture coverage, the calculator calls for eight fixtures. At 650 watts each and 12 hours per day, that is a 5.2 kW lighting load before other equipment is considered.