Animal-based measures, identified on the basis of scientific evidence, can be used effectively in the evaluation of the welfare of on-farm pigs in relation to laws, codes of practice, quality assurance schemes and management. Some of these measures are also appropriate for ante-mortem inspection and there are additional post-mortem animal-based measures which can be taken at the slaughterhouse. Non-animal-based measures can be used when the association between them and the welfare outcome is strong and when they are more efficient than animal-based measures as a means to safeguard welfare. Both animal-based and non-animal-based measures can be useful predictors of welfare in pigs. In order to assess welfare, a wide range of measures is needed. However, to assess aspects of welfare it is unnecessary to use all animal-based measures on every occasion. The choice of animal-based measures will depend upon the specific objectives of the assessment. The full list is comparable to a ‘toolbox’, from which the appropriate range of measures can be selected. The Welfare Quality® protocol provides information on the majority of the welfare outcomes of the main hazards identified in the EFSA Scientific Opinions but not those where time limitation prevents it. There are currently insufficient animal-based measures to use as welfare outcome indicators on-farm or in the slaughterhouse to assess the issues of pain, frustration and other positive and negative emotional states. The extent to which short-term management can prevent the negative effects of hazards arising from genetic selection, and of most housing-related problems, is extremely limited. Herd monitoring and surveillance programmes should be implemented within the pig industry using a range of appropriate animal-based measures to document welfare changes over time. There should be both initial and ongoing training of assessors to ensure valid and reliable welfare measurement.