Magnetkraftrechner

Ziehkraft bei verschiedenen Luftabständen

Pull force drops quickly once a gap opens between the magnet and what it holds. For example, even a thin coating or a sheet of paper matters. The table below applies your current inputs to a series of common gap sizes.

Luftspalt (mm)	Ziehkraft (N)	Ziehkraft (kgf)

Wie man dies berechnet

The tool uses the mirror-image method to estimate the force. Then it adds a small contact gap, because real surfaces never touch perfectly.

Step 1: Treat the Steel as a Mirror

First, the tool treats the steel plate as a thick, flat mirror with very high permeability. As a result, the plate pulls on the magnet exactly as a mirror-image magnet would. In other words, the pull force equals the force between the magnet and its image.

Step 2: Add Up the Pole Forces

Next, the tool models the magnet and its image as four uniformly charged pole faces. It adds the attraction and repulsion between every pair of faces. This method includes edge effects and the way the field spreads as the gap grows. Therefore, it follows the real force curve better than the simple formula F = B² A / (2 μ₀).

Reference: G. Akoun and J.-P. Yonnet, "3D analytical calculation of the forces exerted between two cuboidal magnets," IEEE Transactions on Magnetics, vol. 20, no. 5, pp. 1962-1964, 1984.

Step 3: Holding to an Identical Magnet

Choose this mode to see two identical magnets pulling on each other. The tool then uses the real second magnet instead of a mirror image. At contact, the force matches the steel case. However, at the same gap, the force is higher. The real second magnet sits at the gap distance. A mirror image sits at twice that distance.

Step 4: Add the Effective Contact Gap

Real surfaces never touch perfectly. Coatings, roughness and small flatness errors leave a tiny gap, even in bare contact. Therefore, the tool adds an effective contact gap to your air gap. The force drops steeply near contact, so even a small gap matters. The default of 0.15 mm is an estimate. Set it from your own pull tests.

Steel Thickness Check

In steel mode, the tool also checks your steel thickness. First, it estimates the magnet's flux. Then it finds how thick the steel must be to carry that flux below 1.5 T. Above roughly this level, low-carbon steel starts to saturate. If your steel is thinner, the tool shows a warning. In that case, the real force falls below the value shown. The tool does not correct the number, because predicting that loss needs testing or FEA.

Schiefe Kraft

In steel mode, the tool estimates sliding (shear) force as 20% of the pull force. This is a common rule of thumb for a magnet on clean, dry steel. However, it does not come from the same field model. It also varies a lot with surface condition.