Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here




Can anyone tell me how to calculate coil inductance?

Thank you very much!!


Static approach to calculation of the coil inductance:
L = phic/I = N x phi/I = squareN x I/(Rm x I) = SquareN/Rm
L is coil inductance in Henries
phic is coil flux due to I in Webers
I is coil current in Amperes
N is number of coil turns
Rm is reluctance of the coil core, in 1/Henry, which has to be calculated since it varies from a coil to coil shape. It can be
Rm = Ls/(mu x muo x S)
Ls is path of magnetic flux inside coil in meters
mu is relative permeability of the media in per unit
muo is vacuum permeability = 4 x PI x 10 to Exp(-7) in Henry/meter
S is coil cross-sectional area in square meters

Dynamic approach is
Ecoil(t) = L x (di/dt) in volts
L = Ecoil(t) / (di/dt) in Henries
di/di is a derivative of current according to time t


Small correction (I beg your pardon):
di/di is supposed to be di/dt


Additional minor correction: in JBARTOS terms "phic=phi x N"
is not a flux, but a "flux linkage"


Suggestions to the previous posting marked ///\\\:
Additional minor correction: in JBARTOS terms "phic=phi x N"  is not a flux, but a "flux linkage"
///Thank you for the correction. I did not see it as the "flux." I saw it as "coil flux," which I posted, namely:
phic is coil flux due to I in Webers
In fact, the IEEE Std 100-200 "Dictionary" states:
Flux Linkages. The sum of the fluxes linking the turns forming the coil, that is, in a coil having N turns, the flux linkage is:
lambda=fi1 + fi2 + .... +fiN
fi1 is flux linking turn 1
fi2 is flux linking turn 2
fiN is flux linking Nth turn.
I see that the standard is referring to the sum as flux linkages and flux linkage. I called it the coil flux.
Also, the magnetic flux:
fiA=integral over area A of (B dot product dA)
where A is area, dA is the element of A, and B is magnetic induction at the element dA. This could be applied to the coil N times to obtain coil flux or coil flux linkages.\\\


  Inductance calculatio of a coil is not easy at all. Its value depends on winding geometry and on the magnetic properties of sourrounding material. All designs want a prototype for testing and correcting actions.
  Nevertheless, in some particular cases, very good approaches can be got. For instance, for a single layer coil of circular turns on the free air, the inductance is approx.:

      L = N^2.[R^2/(9.R+10.l)] microhenries
   N:   Number of turns
   R:   Half of diameter of coil between center of conductors (inches)
   l:   Length of coil (inches)

 More details can be found on different manuals like "Reference data for radio engineers" Howard W. Sams & Co., Inc.



Suggestion: Reference:
Arthur R. Bergen "Power Systems Analysis," Prentice-Hall, Inc., Englewood Cliffs, New Jersey 07632, 1986, p. 55 indicates that
lambda=N x fi
lambda = flux linkages in Weber turns
fi = flux that links all the N turns of the coil
Figure 3.1 illustrates leakage fluxes in addition to the flux fi that links all the turns N. Now,
lambda= fi1 + fi2 + .. + fik + .. + fiN
where fik is the flux linking the kth turn of the coil with N turns. It appears that lambda represents flux linkages of the coil and the flux linkages form the coil flux without counting the flux leakages.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close