The Portsmouth yardstick (PY) scheme is a system of handicapping used in yacht racing and dinghy racing. It is administered in the UK by the Royal Yachting Association, based on annual input from a large number of affiliated sailing clubs. In the United States it is administered by the Portsmouth Numbers Committee.

Each class of boat is assigned a PY number, with fast boats having low numbers and slow ones high numbers - so, for example, a 49er might have a PY of 747 while a Mirror has a PY of 1386. (These are the actual PY numbers for 2003, but note that adjustments are made each year.) In a race involving a mixed fleet, finishing times can be adjusted using the formula c = (r*1000)/PY, where c = corrected time and r = recorded time.

See the RYA website [1] for current PY ratings for all types of boats, and the rules for drawing these up. In the U.S., the Portsmouth Numbers Committee has web space at U.S. Sailing:[2]