Calculate the cubic volume of a room for HVAC and fans.
Room volume is length times width times ceiling height, and it is the number HVAC and ventilation work from rather than floor area. That distinction matters because floor area alone cannot distinguish a 200 sq ft room with an 8 ft ceiling from the same room with a 14 ft vault, and the second contains 75% more air to heat, cool and filter. The airflow figure converts volume into cfm at five air changes an hour, the common target for a living space with active filtration: volume times ACH divided by 60. The cubic metre conversion is there because most European equipment — extract fans, air conditioners, air purifiers — is rated metrically.
Room Volume
Volume = length x width x ceiling height x rooms; cubic metres = cu ft x 0.0283168; airflow cfm = volume x 5 / 60
Because they move air, and the amount of air in a room depends on its height. Two rooms with identical floor plans and different ceilings need different equipment.
Use the average height — the mean of the lowest and highest points for a simple slope. For a complex vault, split the room into a box plus a triangular prism and add the two.