You can use our spring calculator to calculate the spring's initial tension as well as spring rate and working loads. You may also measure spring tension by using a scale. Initial tension will be exhausted when the extension spring’s coils extend enough to where you are able to see light in between the coils. The diagram to the right shows how to calculate your spring’s rate using the values from your working loads as well as the initial tension. You must subtract the initial tension from the load and divide the result by the distance traveled from your length inside hooks to the total extended length.