Magnet Calculator

Surface field, magnetic moment and estimated pull force for block, disc and ring magnets.

Formulas used

1. Surface flux density B (Gauss, on-axis at pole face)

Disc B = (Br / 2) · T / √(R² + T²) × 10&sup4;
Block B = (Br / 2) · [ 1 − (2/π)·atan( L·W / (2·T·√(4T²+L²+W²)) ) ] × 10&sup4;
Ring B = B_disc · (A_out − A_bore) / A_out

Br = remanence of the grade (N35–N52: 1.17–1.45 T). R = D/2, L/W/T in mm. Thin plate → 0; thick block → Br/2 (long prism limit).

2. Magnetic moment m (A·m²)

m = (Br / μ₀) · V

μ₀ = 4π×10⁻₇ H/m. V = magnet volume (m³). Equivalent G·cm³ = m × 1000.

3. Pull force F (Newton, Maxwell stress + image method)

F = 2 · B² · A / μ₀

B = surface field (Tesla), A = pole-face area (m²). Theoretical at zero gap; real contact force runs 30–50% below this. kgf = F / 9.80665, lbf = F / 4.44822.