The active coils are the coils which have some space between them and the next coil.
That space gives room for the spring to deform and "act like a spring".
The first coils typically are wound touching to form a "seat" for the spring. Those are not active coils.
I would expect the spring calculator will take fractional values but have not tried it. Just plug in some values and see if the results make sense. The fewer the number of active coils input the stiffer the resulting rate should be.
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MACE
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