For those interested in designing / winding their own coils, here are some (hopefully) interesting links.
The articles include formulas, theory, and design considerations.
A number of them have internal links to different coil types (planar, helical, etc).
Some are simply on-line calculators, with or without formulas supplied.
Sorted aphabetically by domain to avoid perception of 'preferred' sites.
http://coil32.net/online-calculators/pcb-inductor-calculator.html
http://deepfriedneon.com/tesla_f_calcspiral.html
http://www-smirc.stanford.edu/spiralcalc.html
http://www.66pacific.com/calculators/coil-inductance-calculator.aspx
http://www.circuits.dk/calculator_planar_coil_inductor.htm
http://www.tesla-institute.com/!app/sim/fscic.php
https://en.wikipedia.org/wiki/Coil_winding_technology
https://en.wikipedia.org/wiki/Electromagnetic_coil
https://www.allaboutcircuits.com/tools/coil-inductance-calculator/
https://www.allaboutcircuits.com/tools/rectangle-loop-inductance-calculator/
https://www.princeton.edu/ssp/joseph-henry-project/induction-coils/Induction_Coils.pdf ; (c.1901)
https://www.researchgate.net/figure...ary-and-ring-coil-as-secondary_fig1_239437242
The articles include formulas, theory, and design considerations.
A number of them have internal links to different coil types (planar, helical, etc).
Some are simply on-line calculators, with or without formulas supplied.
Sorted aphabetically by domain to avoid perception of 'preferred' sites.
http://coil32.net/online-calculators/pcb-inductor-calculator.html
http://deepfriedneon.com/tesla_f_calcspiral.html
http://www-smirc.stanford.edu/spiralcalc.html
http://www.66pacific.com/calculators/coil-inductance-calculator.aspx
http://www.circuits.dk/calculator_planar_coil_inductor.htm
http://www.tesla-institute.com/!app/sim/fscic.php
https://en.wikipedia.org/wiki/Coil_winding_technology
https://en.wikipedia.org/wiki/Electromagnetic_coil
https://www.allaboutcircuits.com/tools/coil-inductance-calculator/
https://www.allaboutcircuits.com/tools/rectangle-loop-inductance-calculator/
https://www.princeton.edu/ssp/joseph-henry-project/induction-coils/Induction_Coils.pdf ; (c.1901)
https://www.researchgate.net/figure...ary-and-ring-coil-as-secondary_fig1_239437242