Originally Posted by trilerian

Most on road 1/10 springs are 20mm now, so I wouldn't compress them 10mm to measure. I would do somewhere around 5mm, but it shouldn't matter too much as the springs are linear and should follow Hooke's law. F=kx, k is the spring constant which you are trying to figure out and x is the distance. I would set your kitchen scale to grams, then compress 5mm. The scale may read something like 450 grams, then you divide by 5 to get the spring constant, which would be 90 g/mm. You can test different compression lengths, just divide by the length and the spring constant should remain very close.