Abstract: Systems and methods for accurately measuring power output of a cyclist using a bike trainer that may be operated by a user for stationary riding when coupled to a conventional bicycle. The systems utilize a power output equation that models power due to resistance of a fan of the bike trainer as well as power due to kinetic energy of the fan. The systems account for operating conditions that affect the power measurements so that more accurate measurements can be provided, thereby improving the training experience of the user. Operating conditions include mechanical drag, temperature, humidity, and atmospheric pressure and/or altitude. The power output equation is dependent on the angular velocity of the fan of the bike trainer and the measured or received operating conditions.