Ponencia presentada en el XIX Congreso Internacional de Acústica (ICA2007), Madrid, 2-7 Sep 2007.-- PACS: 43.58 Vb.The use of radiation force balances is the standardized method for the measurement of ultrasonic power in water, IEC-EN 61161 Ed1. This paper presents and discusses the application of radiation force balances to the measurement of ultrasonic power generated by air-borne transducers. Experimental results from several transducers are presented and discussed.This work has been financed with funds from the CICYT project: DPI-2007–65408–CO2–02. Financial support from CSIC and CAM to acquire, install and put into service the Laboratory of Medical Ultrasound Metrology of Instituto de Acústica is also acknowledged.Peer reviewed