This International Standard specifies a method for estimating the mean release rate of biocide from an antifouling paint over its entire lifetime (in-service period) using a mass-balance calculation. If required, the cumulative total release of biocide over the first 14 days of the specified paint lifetime can also be calculated. This International Standard is applicable to any antifouling paint that releases a biocide. Where an antifouling paint releases, or is assumed to release, more than one biocide, the calculation can be repeated to allow estimates of the release rate of each biocide to be obtained. The calculated estimate of the total amount of biocide released by the coating over its lifetime can be considered as a worst case for the maximum amount released to the environment, and so the calculated mean release rate value should also be considered as the maximum possible mean release rate over the lifetime of the paint. The calculated estimates are suitable for use in general environmental risk assessments, and the application of appropriate correction factors will allow the most accurate and representative environmental risk assessment to be made in the relevant scenario and risk assessment case. There are no minimum or maximum limiting values of release rate which restrict the use of this method. This International Standard is primarily directed towards the release of biocide from antifouling paints that have been applied to ship and boat hulls. It can, however, also be used for estimating biocide release from antifouling paints that have been applied to other objects.