Feller Correction Calculator

This calculator is intended to be used in association with pharmaceutical grade cleanrooms, and not IAQ (indoor air quality) investigations. The calculations are from Janet Macher's article published in the American Industrial Hygiene Association Journal, 50(11):561-568 (Macher, 1989).

Where (Pr) is the probable cfu count

= N = Number of holes in the sample head

= r = Number of enumerated colony forming units

This calculator is intended to be used with multi-jet impactors typically having between 200-400 holes in the sample head.