Select the shape
Choose disc/cylinder, block or ring so the correct fitted equation and dimension fields are used.
GUK Magnetics
Magnetic Force Calculator
Estimate the ideal pull or holding force of a disc, block or ring magnet in direct contact with thick, non-saturated steel.
2. Enter specification
Material and dimensions
Select a material grade to use the configurator's midpoint Br value, or enter Br manually from a data sheet. All dimensions are in millimetres.
Calculation assumption: the magnet is magnetised through thickness H and is in clean, direct, zero-gap contact with either a sufficiently thick, non-saturated steel plate or an identical magnet.
Calculation method and limitations
Method
The calculator uses the same fitted disc, block and ring equations and the same shape/material correction factors as the GUK Magnet Configurator and legacy Magnetic Force Calculator. The model estimates average flux density and applies magnetic pressure using F = B²A/(2μ₀).
Grade mode uses the same room-temperature midpoint Br values as the configurator. Manual mode uses the Br entered from the relevant data sheet.
Model provenance: the fitted equations and factors are inherited unchanged from those GUK tools. No independent external citation or validated universal dimension/aspect-ratio range is currently documented.
Limitations
- Zero air gap only.
- Magnetisation must be through H.
- Not suitable for countersunk, arc or custom profiles.
- Grade midpoint Br values are guidance, not guaranteed batch values.
- AlNiCo is excluded because grade and dimensions alone are insufficient for a reliable pull-force estimate.
- No verified universal dimension or aspect-ratio range is stated for the empirical fits.
- Use measured data for final design decisions.
Understanding the estimate
What the magnetic force calculator tells you
The calculator estimates normal pull or holding force for a disc, block or ring magnet under idealised contact conditions. It can model either one magnet against sufficiently thick, non-saturated steel or two identical magnets in direct contact.
The shape equations are fitted to FEM and published pull-force data. They are useful for comparing specifications and establishing an indicative requirement, but they are not a substitute for testing the magnet, mating material and complete assembly.
Model assumptions
- The magnet is magnetised through height H.
- Contact is clean, flat and at zero air gap.
- Force acts normal to the pole face, not in shear.
- The steel is sufficiently thick and not magnetically saturated.
- Grade-based Br values represent room-temperature midpoints.
Four inputs
How to use the calculator
Work through the specification in order. Once the first calculation has been completed, valid changes update the estimate automatically.
Define the material
Select a supported grade to use its midpoint Br, or switch to manual Br entry when you have data-sheet information.
Enter dimensions
Use millimetres and enter the dimensions that correspond to the selected shape and magnetisation direction.
Review the estimate
Compare the indicative result in newtons and kilogram-force, then assess the real application conditions below.
Dimension guide
Supported magnet shapes
The model assumes magnetisation through H. If the magnetisation direction or geometry differs, the estimate may not represent the intended magnetic circuit.
Disc / cylinder
A circular pole face with magnetisation through the cylinder height.
- D = diameter
- H = height
Block
A rectangular pole face with magnetisation through the block height.
- L = length
- W = width
- H = height
Ring
An annular pole face. The inner diameter must be smaller than the outer diameter.
- D0 = outer diameter
- Di = inner diameter
- H = height
From calculation to application
Why measured force may be lower
The result represents ideal normal separation at zero gap. Small changes to the contact interface or magnetic circuit can have a substantial effect.
Use the estimate to compare options, then test the selected magnet in the actual configuration.
Air gap and surface
Coatings, paint, adhesive, dirt, curvature, roughness or poor flatness create separation and usually reduce force.
Steel thickness
Thin or saturated steel cannot carry the assumed magnetic flux and may give a materially lower measured result.
Material and temperature
Actual Br varies by grade, production batch and temperature. Grade mode uses a room-temperature midpoint.
Load direction
Sliding or shear performance depends heavily on friction and should not be treated as equal to normal pull force.
Reading the output
Newtons, kilogram-force and design loads
Both displayed values describe the same estimated force. Neither value is a rated capacity or safe working load.
Newtons (N)
The newton is the SI unit of force and is normally the preferred value for engineering calculations.
Kilogram-force (kgf)
1 kgf equals 9.80665 N. It is a force equivalent, not the mass of an object the magnet can safely support.
Safety factor
The calculator does not apply a safety factor. Define one appropriate to the load, environment, failure risk and test evidence.
Outside the simple model
When technical review is recommended
Some applications require more than a shape, grade and nominal contact area. Provide drawings and operating information when any of the following apply.
Information that helps
Share the magnet dimensions and tolerances, grade or magnetic requirement, magnetisation direction, coating, mating material, expected air gap and operating temperature.
For an assembly, include the housing or back-iron arrangement, load direction, anticipated quantities and any available drawing or STEP file.
- Countersunk, arc, pot, channel or custom magnet profiles
- Assemblies using housings, back iron, pole pieces or multiple magnets
- Known air gaps, curved contact faces or unusually thin steel
- Shear loads, shock, vibration or safety-critical retention
- AlNiCo or magnetic circuits vulnerable to demagnetisation
- Elevated temperatures or conditions outside the grade data sheet
Common questions
Magnetic force calculator FAQs
Short answers to the main questions that affect how the estimate should be interpreted.
Will the calculated force match the force measured in my application?
Not necessarily. The calculation assumes clean, flat, zero-gap contact with thick, non-saturated steel or an identical magnet. Coatings, tolerances, temperature, steel thickness, surface condition and the test method can all reduce measured force.
Should I select a grade or enter Br manually?
Selecting a grade is quickest and uses the same room-temperature midpoint Br value as the GUK Magnet Configurator. Use manual mode when you have a specific approved data-sheet value or need to compare values within a published Br range.
Does a coating reduce magnetic pull force?
A coating adds separation between the magnet and mating surface. Even a small additional air gap can reduce force, particularly where other layers such as paint, adhesive or protective films are also present.
Is kilogram-force the weight a magnet can safely hold?
No. Kilogram-force is another way of expressing force. It is not a safe working load, does not include a safety factor and should not be used on its own to determine the mass that an assembly can safely retain.
Why does the calculator assume magnetisation through height H?
The fitted disc, block and ring equations use H as the magnetic length through the pole faces. A different magnetisation direction changes the pole geometry and requires a different model.
Why is AlNiCo not included in grade mode?
AlNiCo has relatively low coercivity and its performance depends strongly on geometry and the complete magnetic circuit. Grade and dimensions alone are insufficient for a reliable pull-force estimate.
Next step
Turn the estimate into a clear specification
Use the Magnet Configurator to organise the geometry, material and application requirements, or send your drawing and operating information to GUK Magnetics for manufacturability and magnet-selection review.