NdFeB density and magnet weight calculator

Use the density of the actual material

For preliminary calculations on a simple sintered NdFeB part, 7.5 g/cm³ is a useful stated assumption. It is not a universal acceptance value. K&J lists 7.4–7.5 g/cm³ for its sintered material reference, while other suppliers publish different typical ranges. Check the actual material sheet when the mass or fit is important.^{[1] [2]}

Do not substitute the density of elemental neodymium. NdFeB is an alloy material system. Bonded magnets contain magnetic powder and a binder; the resulting density depends on formulation and forming. Magnequench’s MQ1-4 compression-bonded material lists 5.9–6.2 g/cm³, illustrating why the sintered assumption cannot be applied to every NdFeB product.^[3]

Units can look deceptively similar. A density of 7.5 Mg/m³ equals 7.5 g/cm³ and 7,500 kg/m³. A supplier may also use lb/in³: multiply that value by approximately 27.6799 to obtain g/cm³. The unit must travel with the number.^{[4] [5]}

Calculate a first mass estimate

Choose the geometric model that actually describes the solid material. For an arc, this calculator uses outer and inner radii, not diameters, and a constant axial length. It does not model a skewed segment, varying section or compound curvature.

Volume formulas with dimensions in millimetres

If V is in mm³ and density ρ is in g/cm³, divide the volume by 1,000 to convert it to cm³:

Mass in grams = V × ρ ÷ 1,000

These are geometric derivations. Keep the units consistent before entering values. Treating a diameter as a radius makes the circular area four times too large.

The examples explain the calculation; they are not available-stock specifications or measured product weights.

Where the estimate stops being sufficient

Nominal dimensions omit dimensional variation and features such as chamfers, countersinks and extra holes. Coating adds material; a housing, adhesive or insert can change the assembly weight substantially. Do not use nominal part mass as package gross weight or a freight chargeable-weight calculation.

For a large production quantity, small per-piece differences accumulate. Use the agreed density or a measured sample mass where required, and separate the magnet, complete assembly and packaging in your records. A simple scale reading does not prove the magnetic grade.

Send the drawing, material route and whether the requirement is an estimate or a measured mass limit. Our inspection guide helps connect the part definition to an acceptance method.