A novel method is presented to determine the order and magnitude of chirps in ultrashort laser pulses based on the ratio of interferometric auto-correlation(IAC) envelope, which is highly sensitive to the chirps.By analyzing and calculating the ratio, the order of chirps and the center halfwidth of IAC envelope ratio as a function of the chirp magnitude for different order chirps are obtained.As an example, the chirp of a short pulse dye laser is determined with the method.In this laser, a square chirp puls...