They are working off an average weight for a standard bike and the 5-7kg is a reasonable average to add-on for an ebike.
All good baseline estimates, but other calculators will give you greater control as they allow for more detailed inputs such as rider weight, bike weight, weight bias, riding style - such as the one CrainN linked and the one on RideFox.
If you are between coils, try other calculators but ultimately... coil can be hard to figure out, based on the fixed increments. And you have to factor in that most of the commonly-available springs will have a high degree of variance from their stated rate.
In most instances, it can be worth getting a Sprindex and playing about with that to get your sag right, then move to a 'fixed' coil from your chosen manufacturer.
Also, if this is for your Rail... consider whether your frame likes a coil. Older generations of Rail were not suitable and in some cases, shocks would touch the frame.