How to Read a Magnet Datasheet: Br, Hcj, BHmax and the Numbers That Actually Matter
A neodymium magnet datasheet packs a lot of information into a small table, and most of it uses units and abbreviations that don’t come up anywhere else in a typical engineering workflow. The result is that a lot of buyers pick a grade by the number after the “N” and hope for the best.
This guide walks through every line of a typical NdFeB datasheet, explains what each value means in practical terms, and points out the handful of places where a misread costs real money — either an over-specified magnet or a part that demagnetizes in the field.
The Four Magnetic Properties on Every Datasheet
Every sintered NdFeB datasheet lists the same four core values. They come in two unit systems — CGS (gauss, oersted, MGOe) and SI (tesla, kA/m, kJ/m³) — and most suppliers print both. Our Magnetic Unit Converter handles the translation if you only have one.
Br — Remanence (Residual Flux Density)
Units: kilogauss (kG) or tesla (T). 10 kG = 1 T.
Br is the flux density left inside the magnet after it has been fully magnetized and the magnetizing field is removed, measured in a closed magnetic circuit. It is the single most-quoted number on a datasheet, and the one most often misunderstood.
What Br tells you: the material’s intrinsic strength. An N52 magnet has a Br of roughly 14.3–14.8 kG; an N35 sits around 11.7–12.2 kG. Higher Br means more flux available from a given volume of magnet.
What Br does not tell you: the field you’ll measure at the magnet’s surface. A gaussmeter held against the face of an N52 disc will typically read 4,000–6,500 gauss, not 14,500. Surface field depends on the magnet’s shape and aspect ratio, and it’s always far below Br. If a supplier claims “14,000 gauss” for a bare magnet, they’re quoting Br as if it were surface field.
Hcb — Coercivity (Normal Coercive Force)
Units: kilo-oersted (kOe) or kA/m. 1 kOe ≈ 79.6 kA/m.
Hcb is the reverse field strength required to bring the magnet’s flux density (B) to zero. For NdFeB, Hcb is always a little less than Br when both are expressed in CGS units — an N52 with Br of 14.5 kG will have an Hcb around 10.5–11.5 kOe.
In practice, Hcb is the least useful of the four numbers for grade selection. Its main role is defining the shape of the normal demagnetization curve, which matters for circuit design but rarely drives a purchasing decision.
Hcj — Intrinsic Coercivity
Units: kOe or kA/m.
Hcj is the reverse field required to bring the magnet’s magnetization (J or M) to zero — in other words, to actually demagnetize it. This is the number that determines how well a magnet resists demagnetization from heat, opposing fields, or its own shape.
Hcj is what the letter suffix on a grade encodes:
| Suffix | Min. Hcj (kOe) | Min. Hcj (kA/m) | Typical max operating temp* |
|---|---|---|---|
| N (none) | ≥ 12 | ≥ 955 | 80 °C |
| M | ≥ 14 | ≥ 1,114 | 100 °C |
| H | ≥ 17 | ≥ 1,353 | 120 °C |
| SH | ≥ 20 | ≥ 1,592 | 150 °C |
| UH | ≥ 25 | ≥ 1,990 | 180 °C |
| EH | ≥ 30 | ≥ 2,388 | 200 °C |
| AH | ≥ 33–35 | ≥ 2,626–2,786 | 230 °C |
*Maximum operating temperature assumes a reasonably “fat” magnet (permeance coefficient ≥ ~1). Thin magnets and magnets in opposing fields derate lower — see the temperature section below.
Two grades can have identical Br and BHmax and behave completely differently once they get warm. An N42 and an N42SH deliver the same flux at room temperature; only the SH survives a 140 °C motor housing.
BHmax — Maximum Energy Product
Units: mega-gauss-oersted (MGOe) or kJ/m³. 1 MGOe ≈ 7.96 kJ/m³.
BHmax is the largest product of B and H along the normal demagnetization curve — the peak energy density the material can deliver into a magnetic circuit. It’s also where the grade number comes from: N52 has a BHmax of roughly 49–53 MGOe, N42 sits at 40–43, N35 at 33–36.
BHmax is a useful shorthand for comparing materials, and it’s the right number for sizing a magnet in a well-designed circuit. It is not a measure of pull force, surface field, or “strength” in any device-level sense. Going from N42 to N52 raises BHmax by about 25% but raises Br — and therefore field and force — by only about 10%.
The Demagnetization Curve and the “Knee”
Better datasheets include a second-quadrant B-H plot showing two curves for each temperature: the normal curve (B vs. H) and the intrinsic curve (J vs. H). The intrinsic curve is flat across most of its length and then drops sharply — that drop is the knee.
As long as the magnet’s operating point stays on the flat portion, any demagnetization from temperature or external fields is reversible; cool it down or remove the field and it recovers. Push the operating point past the knee and the loss is permanent.
Where a magnet’s operating point sits is set by its permeance coefficient (Pc) — essentially its shape. A long cylinder magnetized along its axis has a high Pc and sits comfortably on the flat portion. A thin disc magnetized through its thickness has a low Pc and operates much closer to the knee, which is why thin magnets are the first to lose strength when heated.
For radially magnetized rings, Pc depends on wall thickness relative to the ring’s height and diameter, and on whether the ring is mounted in a back-iron or free-standing. This is one of the reasons a true radial ring and a segmented assembly can specify the same grade and still behave differently in the same motor.
Our Magnets 201 guide covers load lines and permeance coefficient calculations in detail.
Temperature Data
Reversible Temperature Coefficients
Datasheets list two coefficients, both expressed as a percentage change per °C:
- α (Br): typically −0.11 to −0.12 %/°C for all NdFeB grades. A magnet at 100 °C has lost roughly 9% of its room-temperature Br — and gets it back when it cools.
- β (Hcj): typically −0.5 to −0.7 %/°C, with higher-coercivity grades toward the lower end of the range. This is the more important number: Hcj falls five to six times faster than Br, so a magnet’s demagnetization resistance collapses well before its flux does.
Maximum Operating Temperature and Curie Temperature
The maximum operating temperature is a guideline, not a hard specification — it assumes a specific magnet geometry and no opposing field. The Curie temperature (roughly 310–340 °C for NdFeB) is the point at which the material loses its magnetism entirely, and it’s essentially irrelevant to selection because a magnet is ruined long before it gets there.
Use the Temperature Derating Calculator to check a specific grade and geometry against your actual operating temperature rather than relying on the table value.
Physical Properties
These lines are easy to skim past but matter for fit and function:
- Density: 7.4–7.6 g/cm³. Useful for weight calculations and, if a supplier’s figure is well outside this range, a flag that the material may not be what’s claimed.
- Dimensions and tolerances: Standard sintered NdFeB tolerance is ±0.05 mm on ground surfaces and ±0.1 mm on as-sintered or larger dimensions. Note whether the tolerance applies before or after coating — a NiCuNi plating adds 10–20 µm per surface, which matters for a press-fit into a bore. The Technical Resource Hub has tools for magnet-in-bore fits.
- Coating: Nickel-copper-nickel (NiCuNi) is the default; epoxy, zinc, and parylene are specified for corrosion, salt-spray, or biocompatibility requirements. The datasheet should state coating type and thickness.
- Magnetization direction: Axial (through thickness), diametric (across the diameter), or radial. This is the line most often left ambiguous on drawings and the most expensive to get wrong.
- Pull force: Almost always tested as the force to pull the magnet straight off a thick, flat, mild-steel plate at zero air gap. It’s a useful comparison number between parts from the same supplier and nearly useless between suppliers, because plate thickness and surface finish change the result significantly. The Pull Force Calculator shows how quickly the value falls off with any air gap.
“Typical” Versus “Minimum” Values
Most datasheets present a range for each magnetic property — for example, Br 14.3–14.8 kG. Some present a single “typical” figure. When a design depends on a property, specify the minimum, and confirm the supplier’s grade table is built on minimums rather than typicals. Two suppliers’ “N52” can differ by 2–3% in Br simply because one publishes the floor and the other publishes the midpoint.
For PPAP or validated medical applications, request lot-level test data (a hysteresigraph or permeameter report) rather than relying on the catalog table. Our Compliance Document Center explains what part-specific documentation is available.
A Worked Example
Suppose a datasheet reads:
N42SH — Br 12.8–13.2 kG · Hcb ≥ 12.0 kOe · Hcj ≥ 20 kOe · BHmax 40–43 MGOe · α(Br) −0.11 %/°C · β(Hcj) −0.55 %/°C · Max op. temp 150 °C
Reading it line by line:
- Br ~13 kG — mid-range flux. Roughly 10% less field than an N52 of the same size.
- Hcj ≥ 20 kOe — the SH suffix. This part will hold its magnetization in a 150 °C environment with a reasonable geometry, and shrugs off opposing fields that would partially demagnetize a plain N42.
- BHmax 40–43 MGOe — consistent with the “42”. Energy density is about 20% below N52.
- β −0.55 %/°C — at 120 °C, Hcj has dropped to roughly 20 × (1 − 0.55 × 95 / 100) ≈ 9.6 kOe. Still comfortably above the field this magnet will see in most motor or sensor circuits, which is the whole point of paying for SH.
If the application were a room-temperature holding magnet, this would be an over-spec — a plain N42 or N45 would do the same job for less. If it were a motor rotor or an under-hood sensor, it’s the correct choice.
Quick Reference: What to Check Before You Order
- Grade number and suffix both specified (N42 alone is not a complete spec above 80 °C)
- Minimum, not typical, values used in the design calculation
- Magnetization direction stated explicitly on the drawing
- Coating type and thickness, and whether dimensional tolerance includes coating
- Operating temperature checked against magnet geometry, not just the table max
- Pull force understood as a comparative figure, not a design load
Not sure which grade your application needs? The Magnet Grade Selector walks through it, or send us the drawing and we’ll recommend one.
Frequently Asked Questions
What is the difference between Hcb and Hcj?
Hcb is the reverse field that brings the magnet’s flux density to zero; Hcj is the reverse field that brings its magnetization to zero. Hcj is always the larger value for NdFeB and is the one that governs resistance to demagnetization from heat and opposing fields.
Does a higher N number mean a stronger magnet?
The N number is the maximum energy product (BHmax) in MGOe. A higher number means higher energy density and generally higher Br, but the increase in field or pull force is smaller than the increase in the grade number — N52 produces roughly 10% more field than N42, not 25%.
Why is the surface gauss much lower than Br?
Br is measured with the magnet in a closed magnetic circuit. A bare magnet in open air is self-demagnetizing, and the field at its surface depends on shape — typically 30–45% of Br for a disc or block.
What does the letter after the grade number mean?
The suffix (M, H, SH, UH, EH, AH) indicates the intrinsic coercivity class and, with it, the approximate maximum operating temperature. A plain N grade is rated to about 80 °C; SH to 150 °C; EH to 200 °C.
Can I compare pull force between two suppliers’ datasheets?
Only loosely. Pull force depends on the test plate thickness and finish and the test method, none of which are standardized across suppliers. Compare Br and BHmax instead, and use pull force only to compare parts within one supplier’s catalog.
Radial Magnets stocks over 10 million NdFeB magnets in the U.S. across all standard grades and coercivity classes, including true radially magnetized rings. Request a quote or contact us to discuss your application.
