When calculating how much air to circulate in your grow room, just follow this simple guide:

Size of your room : L x W x H = (m3) x 20

For Example : 2m Grow Tent/Room:

2m x 2m x 2m = 8(m3) x 20 = 160(m3)/hr

or a 1.2m Grow Tent/Room:

1.2m x 1.2m x 1.8m = 2.6(m3) x 20 = 52(m3)/hr.

Its best to go for a fan slightly higher than you need to ensure adequate ventilation.