This paper presents a method for localization of a quadrotor using ultrasound with five receiving nodes and a portable beacon. The time of flight is measured from when the ultrasonic signal is produced to when it is received and triggered through threshold detection. Two different lateration algorithms are explored to determine the position, the analytical trilateration and linear least squares method. The linear least squares algorithm outperforms the analytical trilateration method for static position testing and GPS-denied hover. A new approach named the combined lateration algorithm combines these two methods and has the best stationary standard deviation with 8.0 cm within a one metre radius at a height of 1.77 m. It calculates a successful measurement 93% of the time, which provides an average update rate of 9.3 Hz. Successful autonomous hover and landing is performed using a stationary and moving beacon within a GPS-denied environment.