Steam engines wire wizard give you a close indication for a target build
know that it's for a single coil though so if you mount in parralel halve it I try to target a resistence of 0.4 on it (minimum of 0.3) so when I mount dual coils in parralel it will come out at 0.2 (or 0.15 lowest)
If I'm building a single coil though I'll go straight for that 0.2 resistence
Mount it on an ohm reader before firing tends to come out close to the wire wizard +\- 0.05
After that it's just practice once you've done a few you get to know how many wraps for a build type
I tend to always check though as i always forget unless I've written it down