<h2>Abstract</h2> The objectives of the AIUM/NEMA safety standard and the IEC draft are similar and intended to ensure that sufficient information regarding output of diagnostic ultrasound instruments is available so that users can make informed judgements regarding equipment uses. The objectives of the IEC draft standard are to <ul><li>1.(i) define a group of acoustic parameters which can be measured on a physically practical basis (hydrophones);</li><li>2.(ii) define a second group of parameters which can be derived under certain assumptions from these measurements and called derived intensity parameters;</li><li>3.(iii) define a measurement procedure which may be used for the determination of acoustic pressure parameters;</li><li>4.(iv) define the conditions under which the measurements of acoustic parameters can be made in the frequency range 0.5–15 MHz using calibrated piezoelectric hydrophones. Although a group of exposure parameters has been identified, the IEC does not recommend which is the most relevant for field characterisation.</li></ul> The difference between standards is largely a result of uncertainties in the use of hydrophones at the time of formulating the AIUM/NEMA standard. With the advent of modern high quality PVDF miniature hydrophones the more recent IEC Draft Standard recommends specification of the acoustic field in terms of acoustic pressure which is directly measured with a hydrophone. The IEC also differs from the AIUM/NEMA standard for acoustic labelling, where the quantity measured by miniature hydrophones is defined as acoustic pressure and prefers not to use intensity which is derived from plane wave approximation.