Magnitude may refer to:

• Magnitude (mathematics), the relative size of a mathematical object
• Order of magnitude, the class of scale having a fixed value ratio to the preceding class
• A Euclidean vector is defined by both its magnitude and its direction
• A scalar variable is defined only by its magnitude
• Apparent magnitude, the apparent brightness of a celestial object as observed from earth
• Absolute magnitude, the brightness of a celestial object corrected to a standard luminosity distance
• Photographic magnitude, the brightness of a celestial object corrected for photographic sensitivity, symbol m_pg
• Magnitude of eclipse, the ratio between the apparent angular diameters of the Moon and the Sun during an eclipse
• Richter magnitude scale, a measure of the energy of an earthquake
• Moment magnitude scale, an alternative to the Richter scale for measuring earthquakes