Fiber coils are generally evaluated from the aspect of their temperature performance with the full-temperature zero bias range after being connected to a fiber optic gyroscope system. However, the full-temperature zero bias range can only judge the temperature performance of fiber coils but is less effective to guide their applications. To address this problem, this paper proposes the concept of equivalent asymmetric length (EAL) of fiber coils and the way to evaluate their temperature performance based on it. With quantitative analysis, the paper determines the EAL test method and verifies the feasibility of evaluating fiber coils with EAL and the guiding effect of EAL on fiber coil applications. The results show that EAL is approximately linearly correlated with the full-temperature zero bias range, and the temperature performance of three fiber optic gyroscopes whose symmetry is tuned depending on EAL is improved significantly at a temperature change rate of 1 ℃/min or 2 ℃/min. This indicates that EAL is capable of both accurately estimating the temperature performance of fiber coils and guiding their applications.