The FIA's Formula 1 Commission met in London to confirm reforms for next season.
They decided to cut races from a total of 305 kilometres to 290 kilometres - a reduction they calculated to be two or three laps per race. The FIA and Formula 1 said in separate statements that the cut was an inevitable consequence of an earlier decision to reduce fuel flow in engines.
They also decided to cancel plans for gearbox 'homologation', or conformity across all cars, to "preserve supplier development freedom".
The commission also changed the rules on the fixed three-hour limitation of races impacted by rain interruptions, "to ensure that the spectators have the best possible chance to enjoy a full race if disruptions occur".
The FIA statement said the commission has also made changes to this season's sporting and financial regulations, but offered no details.