Abstract This paper discusses and summarizes post-1994 US and European information on ammonia (NH 3) emissions from swine farms and assesses the applicability for general use in the United States. The emission rates for the houses calculated by various methods show good agreement and suggest that the houses are a more significant source than previously thought. A general emission factor for houses of 3.7±1.0 kg NH 3/ year/ finisher pig or 59±10 g NH 3/kg live weight/year is recommended. For lagoons, it was found that there is good similarity between the field test results and the number calculated by a mass balance method. The suggested annual NH 3 emission factor for lagoons based on field tests at one swine farm lagoon in North Carolina is 2.4 kg/ year/ pig . Emission rates from sprayfields were estimated using a total mass balance approach, while subtracting the house and lagoon emissions. The total emission rates for finishing pigs at the test farm compared well to the total rate established by a mass balance approach based on nitrogen intake and volatilization. Therefore, it was concluded that a mass balance approach can be helpful in estimating NH 3 emissions from swine farms. A general emission factor of 7±2 kg NH 3/pig/year could be developed, which is comparable to general European emission factors, which varied from 4.8 to 6.4 kg NH 3/pig/year.