The Portsmouth Yardstick (PY) or Portsmouth handicap scheme is a term used for a number of related systems of empirical handicapping used primarily in small sailboat racing.

The handicap is applied to the time taken to sail any course, and the handicaps can be used with widely differing types of sailboats. Portsmouth Numbers are updated with data from race results, normally annually. The various schemes are not directly linked, and ratings for the same class can and often do vary in the different schemes.

The most prominent Portsmouth Yardstick systems are probably those administered in the United States by the Portsmouth Numbers Committee, in the United Kingdom by the Royal Yachting Association (RYA) and in Australia by Victoria Yachting.