This paper delineates a new method of determining the coordinates of sensors with a single beacon for both the parallel and non-parallel state situations. Cayley-Menger determinant is mostly used when the beacon and deployed sensors are in the state of parallel planes. We have, however, proposed a mathematical model to compute the coordinates of the submerged sensors even when these sensors and beacon are in non-parallel state configuration. As the knowledge of precise coordinates of the sensors is as important as the collected data in underwater wireless sensor networks, the measure of exact distance between the nodes becomes the prime factor for improved accuracy. The proposed mathematical model of coordinate-determination has better immunity from multipath fading and linearization process of non-linear equations, resulting in more precise location of the sensors. Moreover, a single beacon is used to determine the coordinates of the sensor nodes where none of them have a priori knowledge about their locations.