The general rule of thumb is that every 1,000 mg of ozone production will treat 1,000 ft3, which is roughly a 10' x 10' room with 10' high ceilings. Of course, the severity of the problem (usually determined by smell for an odor) is a determinant of the ozone output or exposure length required to remediate the area. For instance, a skunk odor requires more treatment than a casual cigarette lit in an otherwise 'clean' room. An additional consideration concerns whether the treatment area is a vacant space with hard surfaces, or a furnished space with porous surfaces (like carpeting, drapes, furniture, etc,). The more porous materials in the treatment area, the more ozone exposure is required to get an effective treatment.
Also remember that once it gets to the recommended dosage, it still needs to sit at that level for a while to actually react with all the little nasties.