Obi (martial arts)

Many Japanese martial arts feature an obi as part of their exercise outfit. These obis are often made of thick cotton and are about 5 cm wide. The martial arts obis are most often worn in the koma-musubi knot (square knot); in practice where hakama is worn, the obi is tied in other ways.

In many martial arts the colour of the obi signifies the wearer's skill level. Usually the colours start from the beginner's white and end in the master's black, or red and white.

Aikido

Unlike in many other martial arts, adult practitioners of aikido do not wear coloured obis, though in some schools different colour codes have been formed, especially for children. The children's obis range from white for beginner level to 5th kyū, other colours for the rest of the kyū levels, and black for levels 1st dan and up.

In some aikido schools, wearing a hakama is a privilege earned by reaching the first dan level. In other schools, all practitioners may wear a hakama. After taking up using a hakama, the colour of obi does not matter since it will be covered by the hakama.