Magnet Pull Force Calculator
SI
Imp
Imperial
Inputs
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Magnet grade
(grade)
Representative remanence values for common permanent-magnet materials. Use supplier data when you have it.
N35 neodymium (Br ~1.20 T)
N42 neodymium (Br ~1.32 T)
N52 neodymium (Br ~1.45 T)
Ceramic / ferrite 5 (Br ~0.39 T)
SmCo 26 (Br ~1.05 T)
Custom remanence
Custom Br
(B_r)
Custom residual flux density / remanence in tesla from the magnet datasheet.
T
Magnet shape
(shape)
Shape only sets the pole area. Magnetization is assumed through the thickness.
Disc / cylinder
Block / rectangle
Diameter
(d)
Circular pole diameter for a disc or cylinder magnet.
mm
Width
(w)
Rectangular pole width.
mm
Length
(l)
Rectangular pole length.
mm
Magnet thickness
(t)
Magnet dimension in the magnetization direction.
mm
Air gap / coating
(g)
Effective nonmagnetic gap from air, paint, plating, adhesive, unevenness or protective film.
mm
Circuit efficiency
(k_c)
Derates Br to a practical contact-face flux density. Lower it for thin magnets, open flux paths and non-ideal geometry.
%
Target/contact factor
(k_t)
Derates pull for steel thickness, surface finish, roughness, paint, curvature, edge fringing and nonuniform contact.
%
Safety factor
(SF)
Pull force is divided by this value to estimate a safe working load.
Results
Default result
Edit inputs
Safe working load
(SWL)
17.64
N
Pass
3.966 lbf
Also computed
Estimated pull force
(F_pull)
Pass
52.92
N
11.9 lbf
Equivalent held mass
(m_hold)
1.799
kg
Gap flux density
(B_gap)
Pass
0.84
T
Contact flux density
(B_contact)
0.924
T
Gap derating
(k_g²)
82.64
%
Pole area
(A)
314.2
mm²
Magnetic pressure
(p_m)
0.2807
MPa
Remanence used
(B_r)
1.32
T
Show 2 more results
Pull force vs Air gap
Small gaps, paint, coatings and surface roughness dominate permanent-magnet pull force. Use the curve to see how quickly the screening force falls with clearance.
Pull force vs Air gap
0
20
40
60
80
0
2
4
6
8
working gap
Air gap (mm)
Pull force (N)
Small gaps, paint, coatings and surface roughness dominate permanent-magnet pull force. Use the curve to see how quickly the screening force falls with clearance.
Method notes
3 notes
Screening model uses B_gap = Br*k_c*t/(t+g), then F = B_gap^2*A*k_t/(2*mu0).
Grade Br values are representative; supplier pull-force data or measured tests should control final selection.
Real pull depends on magnetization direction, keeper geometry, steel thickness, edge fringing, temperature, coatings, sliding/shear loads and the magnet B-H curve.
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