A method of determining the tension in a guy wire or other flexible member. The first 15 natural frequencies for the design tension and tensions at 1 percent increments above and below the design tension are calculated. The actual first 15 natural frequencies are then determined, and the tension in the wire is the one whose calculated frequencies are most similar to the actual frequencies. The method is sensitive enough to use the wind to excite the wire or it can be manually struck to produce vibrations.