1. Size; extent; dimensions: to determine the magnitude of an angle.

2. Great importance or consequence: affairs of magnitude.

3. Greatness of size or amount.

4. Moral greatness: magnitude of mind.

5. Astronomy.

In mathematics:

- Magnitude (mathematics), the relative size of a mathematical object.
- Magnitude (vector), a term for the size or length of a vector.
- Scalar (mathematics), a quantity defined only by its magnitude.
- Euclidean vector, a quantity defined by both its magnitude and its direction.
- Order of magnitude, the class of scale having a fixed value ratio to the preceding class.

In astronomy:

- Magnitude (astronomy), a measure of brightness and brightness differences used in astronomy.
- 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 mpg
- Magnitude of eclipse or geometric magnitude, the size of the eclipsed part of the Sun during a solar eclipse or the Moon during a lunar eclipse.

As an earthquake unit of measure:

- Richter magnitude scale,a measure of the energy of an earthquake.
- Moment magnitude scale, an alternative to the Richter scale for measuring earthquakes.

1. Short for "Magnetic Attitude"

2. Attractive personality