Magnet Pull Force Calculator

Estimate a permanent magnet's holding force in direct contact and across an air gap, from its grade and dimensions.

ModelB²A / 2μ₀

Targetthick mild steel

Unitsmm / N

01 Magnet

Material / grade

Shape

Diameter × thickness

Dimension units

02 Air gap & target

Gap between magnet and steel

0 mm = direct contact. Drag the slider or type an exact value.

Working-load safety factor

Assumes a flat, clean, low-carbon steel target at least as thick as the magnet. A thinner or painted target, or a rough/curved surface, will hold with noticeably less force.

Estimated pull force at 0.0 mm gap

0 N

0 kgf 0 lbf

Recommended working load (2× derate) 0 N

Idealized estimate. Accounts for self-demagnetization from the magnet's own aspect ratio (thin, wide magnets fall well short of B_r at the pole face — see below), but not surface finish, coatings, curvature, or a target thinner than the magnet. Real tested pull force can still run meaningfully lower. Treat this as an upper bound, not a guarantee; check manufacturer pull-test data for critical work.

Pull force vs. air gap

Current setting highlighted in orange. Hover the curve to read any point.

Modeled force Current gap

View sampled values as a table

Gap	Force (N)	Force (kgf)	Force (lbf)

How this is calculated

The textbook magnetic-pressure equation gives the ceiling force if the magnet reached its full remanence (B_r) at the pole face:

F₀,ideal = B_r² · A / (2 · μ₀)

where A is the pole-face area and μ₀ = 4π×10⁻⁷ T·m/A. Real magnets fall short of this because a finite-thickness magnet partially demagnetizes itself — how much depends on its permeance coefficient (Pc), which is set by its aspect ratio. A thin, wide magnet has a low Pc and operates well below B_r; a thick, narrow one has a high Pc and gets close to it. Pc is approximated from a curve fit to published reference points for cylindrical magnets (Pc ≈ 3.46·(L/D)^1.2, using the equivalent diameter of the pole face for non-round shapes), evaluated at twice the magnet's thickness — a magnet flush on a thick steel keeper behaves like double its own thickness in free space, since the keeper mirrors it. That gives the actual contact force:

F₀ = F₀,ideal / (1 + 1/Pc)²

Force across a gap extends the same circuit by adding the air gap (x) as a further reluctance in series with the magnet's thickness (L_m):

F(x) = F₀,ideal / (1 + x / L_m + 1/Pc)²

This tracks measured curves reasonably well at small gaps but tends to overstate force as the gap grows large relative to the magnet, and the Pc curve fit is itself an approximation (exact permeance coefficients need an elliptic-integral or FEA solution). For mission-critical designs, validate against a manufacturer's tested curve or an FEA tool.