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Calculate magnetic flux from magnetic flux density and effective area. This tool is useful for estimating pole-face flux, air-gap flux, sensor area flux, magnetic circuit comparison and early-stage magnet or motor design checks.
The calculator uses the basic magnetic flux equation. It is most accurate when B is the average flux density over the selected area and the field is approximately perpendicular to that area.
| Item | Formula | Engineering Notes |
|---|---|---|
| Magnetic Flux | Φ = B × A × k | B is flux density in tesla, A is area in square meters, and k is the utilization factor. |
| Round Area | A = π × (D / 2)2 | Use the effective pole-face diameter. Dimensions are converted from mm to meters. |
| Rectangular Area | A = L × W | Use the effective pole-face length and width, not necessarily the full part envelope. |
| Ring Area | A = π × ((OD / 2)2 - (ID / 2)2) | Useful for ring magnets, annular pole faces and circular magnetic circuits with a center hole. |
| Unit Conversion | 1 T = 10,000 G; 1 Wb = 108 Mx | Use tesla and square meters internally to avoid unit mistakes. |
Magnetic flux represents the total field passing through an area. It is useful for magnetic circuit comparison, but it should not be confused with pull force, surface field or magnetic moment.
For final engineering, use measured flux density, FEA results or air-gap flux density from the actual magnetic circuit. Br values are material references and do not directly equal external useful flux in all applications.
| Input Type | Typical Range | When to Use | Important Caution |
|---|---|---|---|
| Measured surface B | 0.05 - 0.6 T typical near magnet surface | Quick comparison of magnet pole face or holding magnet surface | Depends heavily on probe position, magnet shape and measurement gap. |
| Air-gap B | 0.2 - 1.2 T in many magnetic circuits | Motors, actuators, magnetic couplings and magnetic circuits | Should be average flux density over the effective area. |
| NdFeB Br | 1.17 - 1.45 T approx. | Material-level estimate or early comparison | External useful flux is lower because of demagnetization and leakage. |
| SmCo Br | 0.85 - 1.10 T approx. | High-temperature and corrosion-resistant magnet design | Lower Br than NdFeB but stronger temperature stability. |
| Ferrite Br | 0.35 - 0.42 T approx. | Cost-sensitive or larger-volume magnetic circuits | Often requires larger area or magnetic circuit support. |
The formula assumes average B over the area. A single peak surface field measurement may overestimate total useful flux.
Even a small gap can reduce useful flux and spread the field outside the target area.
If the return path or pole piece saturates, increasing magnet strength may not increase useful flux proportionally.
Use the effective magnetic area, not always the full mechanical outer size of the part.
Br is a material property measured under defined conditions. The working flux density in a real circuit is usually lower.
Magnet Br decreases with temperature, so hot operating conditions reduce flux compared with room-temperature estimates.