Flight time is a key aspect for ubiquitous deployment of unmanned multi-copters. The duration of flight depends on on-board component efficiency along with the battery capacity of the multi-copter. The propulsion system (motor and propeller) of the multi-copter consumes more than ∼60% of the battery energy. In this paper, we present a novel algorithm for finding an energy-efficient path between two waypoints in three dimensional space. The algorithm takes into consideration the mechanical and electrical properties of its propulsion system along with the dimensions of the obstacle space to determine an energy efficient flying path. Through detailed simulations of real world flying scenarios we demonstrate that our algorithm provides ∼30 % energy savings for mid-range flights as compared to traditional line-of-sight approaches.