The design of the exhaust ports of a two-stroke cycle engine is mainly based on the area required to reduce the cylinder pressure at the end of the expansion stroke to scavenge air pressure in the minimum practicable time. The flow through the exhaust ports is both sonic and subsonic; in the former case the flow is independent of the exhaust pipe conditions but not in the latter case. In the first stage of the design, however, the exhaust pipe conditions may be assumed to be constant when calculating the port area, subsequent calculations of the pressure drop allowing for the pipe size may then be made by the methods suggested by Wallace, Cole, or Benson. In the following Note formulae are developed for estimating the port area neglecting the exhaust pipe size.