How fast do stars of different types spin?

Spectroscopic studies of hundreds of stars in each spectral type from O to M has shown over the years that the 'early-type' stars of classes O, B and A have rotational velocities between 200 and 350 km/sec, and that at spectral type F, there is a rapid decline from about 100 km/sec at F0 to 10 km/sec at G0.

The Sun, a G2 star rotates at about 2 km/sec, and red giants which are over 100 times larger than the Sun rotate at 1 km/sec and slower.

The fastest rotation rates are seen in neutron stars which have speeds of 1000s of km/sec.

For normal stars, it has been proposed that magnetic breaking for stars of type F, G and later is much more efficient that for stars of types O, B and A when the stars were being formed out of dust clouds. Also, the existence of planets has been proposed as a sign of an efficient breaking mechanism since, if you added the angular momentum of the planets in our solar system, back into the sun, the sun would be spinning at 100 km/sec.

The relationship between the age of a star and its rotation rate is sufficiently accurate that astronomers can determine the rotation speed of a star, and from its spectral type, determine an age for the star, after allowance is made for the tilt of the star's spin axis relative to the line-of-sight.