Magnetic field lines are the invisible topography around magnets. This simulation draws them in real time for any arrangement of magnetic poles you place, revealing flux density and the characteristic patterns of dipoles, monopoles and quadrupoles.
Each field line traces the direction of the net magnetic force using the Biot-Savart law. Positive poles (red) radiate outward, negative poles (blue) converge inward, and the line density indicates field strength. Equipotential contours can be toggled on.
Left-click to add a north pole, right-click for a south pole. Drag poles to rearrange them. The field redraws live. Delete a pole by right-clicking an existing one or using the Reset button.
Earth's magnetic field resembles a dipole tilted ≈11° from the rotation axis. Every 200 000–300 000 years the poles flip — during reversal the field weakens and becomes complex, briefly resembling the chaotic patterns you can create here.