[Dave at Pelican Parts]

If you can mesure the thickness of the wire, and the diameter of the coils, there are formulas that let you calculate at least an approximation.

Or you can use your weight set and a ruler. (And a friend.) Measure the height of the spring with no weight on it. Put the bar of your weight set through the middle (or a broom handle, or ...) and put 50 lbs of weight on the bar so that it rests on the top of the spring. Measure the spring height. (The bar is there to keep the spring upright and keep the weight from sliding off.)

Spring rating is in lbs/in. Find the amount that the spring got shorter when you put the weight on it, and divide 50 by that number.

Repeat with more weights--the more measurements you take the more the errors will average out. Multiple measurements will also tell you if you have a progressive-rate spring.

--DD