INTRODUCTION This Item gives approximate pressure loss information for a wide range of flowmeters operating under turbulent flow conditions. It is assumed that any flow disturbing elements in the pipe line (e.g. valves@ bends@ area changes) are sufficiently far from the meter to have no appreciable effect on its pressure loss. The data are based on information supplied by manufacturers of flowmeters and on the British Standard@ B.S. 1042@ Part 1@ 1964 on flow measurement. The information is presented in the form of a non-dimensional pressure loss coefficient plotted against nominal meter size or@ for differential pressure devices@ against meter area ratio. For differential pressure devices the data given here are accurate to within a few per cent but for inferential and displacement meters it is possible to give only approximate data. There are two principal reasons for this difference. The first arises because there is no standardisation of inferential and displacement meters@ and there is@ in general@ a lack of geometrical similarity between meters of different sizes and from different manufacturers. The second reason arises from fluid dynamic considerations. Figure 1 shows how the presence of a meter may considerably affect the axial pressure distribution in a pipe line. Close to the meter variations around the perimeter of the pipe may also occur. The data given here for differential pressure devices are based on measurements at standardised positions which are in regions of fully-developed flow. For inferential and displacement meters no standard procedures for pressure loss measurement exist and variations in the positioning of the pressure tappings are a probable source of scatter of the data for these meters. It is emphasised that the question of metering accuracy is quite different from the question of the accuracy of the pressure loss data quoted in this Item. The accuracy of metering is not considered here.