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Magnet pull force calculator
Calculate how much a neodymium magnet can hold with confidence.
Choose a shape, enter the dimensions in millimetres, then pick a grade. You get the estimated maximum straight pull against thick, flat steel, a design range around it, and in stock magnets that match. Free to use, no sign-up. Metric in, metric out: millimetres and kilograms, with newtons and pounds alongside.
What this calculator does
MagNet™ is Magnet Store's free online magnet pull force calculator and magnetic field calculator, built in the UK for neodymium magnet selection.
Enter a magnet's shape, size and grade, and it estimates pull force in kilograms-force, newtons and pounds-force, along with gauss and flux density across air gap, temperature, steel and sensor conditions for the most common magnet shapes. It then shows the closest match in stock. It is built for engineers and designers who need a figure they can defend rather than a headline number.
Every pull force result comes with a stated error band, so you get a transparent estimate rather than a bare claim. Verify it in the finished application before relying on it.
Reading your result
The headline figure is the estimated maximum direct pull: the force needed to pull the magnet straight off thick, flat, clean steel with nothing in between.
Pull strength, pull force and holding force all mean the same quantity here. That is how magnet pull is quoted across the industry, and it is a best case. Every real fixing gives some of it back, which is why the calculator prints a design range beside the headline number rather than a single confident figure. Ask it for a size we have no evidence for and it will say so instead of inventing one.
What every figure on this page assumes
- Thick, flat mild steel
- Zero air gap
- Full, clean contact across the pole face
- Centred, axial pull
- Axially magnetised magnet
- Room temperature, around 20 °C
Change any one of those and the real figure drops. It is an estimate for comparing and specifying, not a safe working load.
1 kg of pull = 9.80665 N = 2.2046 lbKilograms here are kilograms-force: the weight the magnet could just hold in ideal conditions. Newtons are the engineering unit. Pounds are there for comparison with suppliers who quote imperial.How to use the calculator
- Pick the shape. Disc or cylinder, block, or ring. Countersunk versions sit under their plain shapes.
- Enter the dimensions in millimetres. Diameter and thickness for a disc; length, width and thickness for a block; outer diameter, bore and thickness for a ring.
- Choose the grade. N42 is the everyday standard. For the same size, N52 comes out roughly 24% higher. Our guide to neodymium magnet grades explains what the numbers and letters mean.
- Read the result. Pull in kg, N and lb, the design range, how the figure was arrived at, and stock that matches what you typed.
Pull force is not a safe working load
The figure is a maximum. It assumes everything is perfect: thick steel, dead flat contact, no gap, and the load pulling straight off the face. Treat it as a ceiling, not a promise.
Engineers derate it, usually heavily. Published rules of thumb for a static load in good conditions commonly sit at around a third of maximum pull, and go lower where there is vibration, sideways loading or any gap at all. There is no single correct factor. It depends on the consequence of failure, the duty cycle and the standards that govern your application, so the number has to come from your own engineering judgement rather than from this page.
For lifting, certified lifting equipment is rated to a fraction of breakaway force under standards such as BS EN 13155. This calculator is not a substitute for that.
Six things that lower magnet pull force in practice
Air gaps
A coat of paint counts. So does a slightly rough surface. Pull falls away steeply with separation, and fractions of a millimetre matter. The air gap tab in the calculator above plots the curve for your magnet.
Steel thickness
The headline figure assumes steel thick enough to carry all the flux. Thin sheet saturates and cannot take the full force. The steel thickness tab in the calculator above shows where that starts to bite.
Steel type and condition
Mild steel is the reference. Stainless grades, plating, paint and rust all take something off, and several stainless steels are barely magnetic to begin with.
Alignment and shear
Quoted pull is straight off the face. Sideways, the magnet holds by friction, so sideways capacity is commonly a fifth to a third of direct pull depending on the surfaces.
Temperature
Standard neodymium weakens as it warms and can lose strength permanently past its rating. The temperature tab in the calculator above separates the reversible loss from the permanent one.
Contact area
A magnet overhanging an edge, or sitting on a narrow strip, cannot use its whole pole face. Pull drops faster than the lost area alone would suggest.
How the calculator works
MagNet™ is a free online magnet pull force calculator that works from evidence, checked against physics. It does not print the output of a single textbook formula, because for real magnets on real steel that formula does not survive contact with measurement.
F = B²A ⁄ 2μ₀Magnetic pressure across a pole face of area A. It is exact for an ideal, perfectly contacting, infinitely permeable circuit, and it sets a genuine physical ceiling. Applied naively to a real magnet on a real plate it overstates pull substantially: flux leaks around the edges, the steel is finite, and contact is never perfect. We use it as a bound, never as the answer.The pull model interpolates within a large specialist reference dataset of magnet performance, several hundred records covering plain axially magnetised discs, blocks and rings across the size envelope below, densest at N42 and N52. Physics informed shape functions carry the size trend between those records, so a size with no record of its own still behaves the way magnetostatics says it should rather than following a curve fitted for its own sake. That evidence base anchors the result. It is not an independent measurement of the item in your hand, which is why every figure ships with a range.
How the estimate keeps itself honest
A physical ceiling
No result may exceed the magnetic pressure limit for the pole area in play. Where sparse evidence would ever push past it, the figure is capped and labelled as capped.
A range sized by evidence
Large magnets carry wider bands than common sizes, because the evidence behind them is thinner.
Evidence before a number
Inside the envelope our evidence covers, you get a figure and a range. Outside it, you get a clear explanation of why, along with a recommendation to test the real thing rather than rely on a number we cannot stand behind.
What sits behind it
Field and gauss figures elsewhere in the tool come from a separate magnetostatic field model, cross checked against closed form solutions and against bench readings. Pull figures are engineering estimates from data, not test certificates. Methodology summaries are versioned; this page was last reviewed on 5 August 2026.
Magnet strength formulas, and what each one tells you
There is no single magnet strength formula that gives real pull. There are several, and each one is true for a different thing.
Three of them carry most of the weight on this page. One sets a ceiling that nothing can pass. One explains why identical material behaves differently depending on the shape it was cut into. One tells you how thick your steel needs to be. None of them on its own produces the number at the top of the page, which is exactly why the calculator works from evidence and keeps the formulas as checks on itself.
Where the magnet actually works
A magnet sits in its own field, and that field pushes back. How hard it pushes depends on shape, through a quantity called the demagnetising factor. The ratio that comes out of it is the permeance coefficient, and it is the load line the magnet has to work along.
Pc = (1 − N) / NN is the demagnetising factor, which depends only on the shape. For a disc, Pc works out close to thickness divided by diameter. Draw that as a line from the origin, cross it with the material's demagnetisation curve, and the crossing point is where the magnet is genuinely operating.Take the same N42 material and cut it into three discs, all 20 mm across, and you get three different magnets as far as the physics is concerned.
| Disc | Pc | Working B | Share of remanence |
|---|---|---|---|
| 20 × 1 mm | 0.14 | 1.6 kG | 12% |
| 20 × 2 mm | 0.26 | 2.7 kG | 20% |
| 20 × 5 mm | 0.58 | 4.8 kG | 37% |
| 20 × 10 mm | 1.11 | 6.9 kG | 53% |
| 20 × 20 mm | 2.21 | 9.0 kG | 69% |
This is the real reason the thickness curve further up bends over. A 1 mm slice is not the same magnet made shorter. It works at 1.6 kG against a remanence of 13.1 kG, and it sits past the knee of its own curve, where a push does not fully come back. Worth knowing before you specify very thin discs for anything warm, or anything that will meet a strong field.
How thick the steel has to be
Flux has to get back to where it came from. Roughly half of what leaves each pole face returns through the plate, and a plate can only carry so much before it saturates, at somewhere near 1.6 T for ordinary mild steel. Put those two facts together and a minimum thickness falls out of them.
For the 20 mm N42 disc used throughout this page that comes to roughly a millimetre. Thicker steel than that adds very little. Thinner steel saturates, and the pull drops away with it, which is the single most common reason a magnet underperforms on a job. The steel thickness tab above runs the same sum for your own size.
Why sideways is different
Out in the middle of a flat plate there is no sideways magnetic force at all. The field is symmetric, so whatever pulls the magnet one way pulls it the other way just as hard, and the two cancel exactly. Nothing magnetic is holding it in place across the surface.
What stops it sliding is friction, and friction belongs to the two surfaces rather than to the magnet. That is why any shear figure is a fraction of the pull, and why it moves so far with coating, finish and dirt. It is also why we give shear as a range and never as a single number.
What temperature does
Neodymium weakens as it warms, and how fast depends on the letters after the grade. Remanence falls by around 0.12% per degree for a plain N grade and around 0.09% for AH. Coercivity falls roughly five times faster, roughly 0.60% down to 0.45% per degree, and coercivity is what decides when a loss stops being reversible. Warm an N42 to 80 °C and roughly 93% of its remanence is left, all of which returns on cooling. Take it past its rating and some of it will not come back.
Shape matters here as well. A thin magnet, low on its load line, begins losing irreversibly 30 to 50 °C earlier than the bare datasheet number suggests, which ties this straight back to the load line above. The temperature tab above covers both halves properly.
How to measure pull force yourself
If you want to check a figure rather than take ours, the method matters more than the instrument.
- Pull straight off the face. Anything off-axis reads low, and it is easy to be off-axis without noticing.
- Pull slowly and steadily. A snatch reads high on a spring balance and low on most digital ones.
- Record the breakaway, the moment it lets go, not the load it sits at happily.
- Clean both faces first. A fingerprint is an air gap, and this page has already shown what those cost.
- Use steel thick enough not to be the limit, or you are measuring the plate rather than the magnet.
- Repeat it five times and quote the spread. One reading is an anecdote.
Do that and your numbers should land inside the design range shown with every result. If they land well outside it, the surface, the steel or the alignment is usually the reason before the magnet is.
What this calculator covers: shapes, grades and sizes
- Shapes
- Disc and cylinder, block, and ring, all axially magnetised, plus countersunk discs and blocks as clearly labelled estimates derived from the plain shapes.
- Grades
- N27 through N55. Evidence is densest at N42 and N52, and grade scaling between them comes from that same evidence: For the 20 × 5 mm disc worked below, N52 comes out at around 24% above N42. The two comparisons people ask for most, N35 vs N42 and N42 vs N52, come out at roughly 20% and 24% for that same disc. Other sizes and shapes differ, so treat those as figures for the example rather than fixed ratios. Grades far from the dense region are labelled with the extra uncertainty they carry. The magnet grades guide covers the naming in full.
- Sizes
- Discs from roughly 1.6 to 76 mm diameter and 0.8 to 51 mm thick. Blocks to around 152 × 76 × 51 mm. Rings from roughly 3.2 to 76 mm outer diameter, with bores up to two thirds of the outer diameter. Proportions outside that envelope are refused rather than estimated.
Typical pull force examples
| Magnet | Grade | kgf | N | lbf |
|---|---|---|---|---|
| 10 × 2 mm disc | N42 | 1.16 | 11.4 | 2.56 |
| 10 × 3 mm disc | N42 | 1.91 | 18.7 | 4.21 |
| 15 × 3 mm disc | N42 | 3.22 | 31.6 | 7.10 |
| 20 × 3 mm disc | N38 | 3.92 | 38.4 | 8.64 |
| 20 × 5 mm disc | N42 | 7.80 | 76.5 | 17.2 |
| 25 × 5 mm disc | N42 | 10.5 | 103.0 | 23.1 |
| 12.7 × 6.35 × 3.18 mm block | N42 | 2.18 | 21.4 | 4.81 |
| 12.7 × 6.35 × 3.18 mm block | N52 | 2.69 | 26.4 | 5.93 |
| 25 × 10 × 5 mm block | N42 | 6.58 | 64.5 | 14.5 |
| 12.7 mm OD × 6.35 mm bore × 6.35 mm ring | N42 | 3.96 | 38.8 | 8.73 |
Estimated maximum direct pull against thick, flat, clean steel with zero gap, in kilograms-force, newtons and pounds-force. Most people search for pull force in "kg", which is the same quantity as kgf here. Every row is the calculator's own output, and in the tool each one carries its design range as well. The two block rows show the grade effect on an identical magnet: +23.4%. After grade by grade tables rather than one exact size? Those live in the magnet grades guide.
Magnet pull force: frequently asked questions
How do you calculate magnet pull force?
For a real magnet the honest answer is: from evidence, not from one equation. Closed form expressions exist for idealised cases and they are useful as bounds, but real pull depends on shape, proportions and grade in ways a one liner misses. This neodymium magnet pull force calculator interpolates within our reference evidence for the exact shape family, scales by grade, and reports the estimate together with the range around it.
What does the kg figure actually mean?
It is the weight the magnet could just support hanging beneath thick steel in perfect conditions: pull straight off the face, no gap, full contact. It is a comparison standard rather than a working load. Design to a third of it or less.
Which is stronger, N35 or N52?
N52. For the same size, expect around 48% more pull than N35. The steps in between are close to even: N42 sits around 20% above N35, and N52 around 24% above N42.
How much weight can a magnet hold?
It depends on size, grade and above all on conditions. For scale: the 20 × 3 mm N38 disc in the table above holds around 3.9 kg in ideal conditions, while large blocks reach three figures. Hanging a weight vertically below a magnet on thick steel is the friendly case. On a wall the same magnet holds far less, because the load is now shear.
Is pull force the same as magnet strength or gauss?
No. Gauss measures field intensity at a point; pull force is a mechanical force against steel. A magnet can read impressively on a gauss meter and still hold very little. People searching for a magnet strength calculator usually mean one of two different things: how hard a magnet holds, which is what this page covers, or how strong its field is at a distance, which is the gauss search tab above. Magnetic strength at the pole and holding force are not interchangeable: a 10,000 gauss reading tells you nothing on its own about what the magnet will hold, because holding also depends on pole area and the steel.
Why does my magnet hold less than the calculator says?
Almost always one of four things: a gap from paint, dirt or curvature; steel that is too thin; sideways loading; or part of the pole face hanging off the steel. Each is covered above, and each has its own calculator.
Can I use this figure for lifting equipment?
No. It is an engineering estimate for design comparison. Lifting needs certified equipment rated under the relevant standards and proven in situ. Estimate here, buy the right magnet, then verify with a physical test in your own application.
Get the magnet, not just the number
Shop disc magnets, block magnets and ring magnets. The calculator's stock matches link straight through to products with the pull you asked for.
Working the other way round, from a force to a size? Use the find-by-pull-force tab in the calculator above.
Need a size we do not stock, or a pull target to hit? Ask for a custom magnet quote and send the calculator's share link with your enquiry, so we start from your exact numbers.
Not sure what your application needs? Talk to our technical team for real answers about grades, gaps and fixings.