A magnetic particle with uniaxial anisotropy has one easy axis. If the easy axis is in the  direction, the anisotropy energy can be expressed as one of the forms:
where  is the volume,  the anisotropy constant, and  the angle between the easy axis and the particle's magnetization. When shape anisotropy is explicitly considered, the symbol  is often used to indicate the anisotropy constant, instead of . In the widely used Stoner–Wohlfarth model, the anisotropy is uniaxial.