Ka is the first consonant of the Indic abugidas. In modern Indic scripts, ka is derived from the Brāhmī letter , which is (according to the Semitic hypothesis) derived from the Aramaic ("K").

Aryabhata used Devanāgarī letters for numbers, very similar to the Greek numerals, even after the invention of Indian numerals. The values of the different forms of क are:

In Tabla notation, क (ka) also seen as कि (ki), or के (ke) is a flat, nonresonant stroke of the left hand. The heel of the hand is left on the drum, while the hand rotates to hit the drum, with the focus of the force being focused between the tips and first joints of the fingers.

के (ke) is the abbreviation used for केतु (Ketu), the descending lunar node. In Hindu astrology, Ketu represents karmic collections both good and bad, spirituality, and supernatural influences. Ketu is associated with the Matsya Avatar (Fish Incarnation) of Vishnu. Ketu signifies the spiritual process of the refinement of materialization to spirit and is considered both malefic and benefic, as it causes sorrow and loss, and yet at the same time turns the individual to God. In other words, it causes material loss in order to force a more spiritual outlook in the person. Ketu is a karaka or indicator of intelligence, wisdom, non-attachment, fantasy, penetrating insight, derangement, and psychic abilities. Ketu is believed to bring prosperity to the devotee's family, removes the effects of snakebite and illness arising out of poisons. He grants good health, wealth and cattle to his devotees.

There are three different general early historic scripts - Brāhmī and its variants, Kharoṣṭhī, and Tocharian, the so-called slanting Brahmi. Ka as found in standard Brahmi, was based on a simple "+" shape, with slight variations toward the Gupta . The Tocharian Ka had an alternate Fremdzeichen form, . The third form of Ka, in Kharoṣṭhī (𐨐) was probably derived from Aramaic separately from the Brahmi letter.

The Brahmi letter , ka, is probably derived from the Aramaic Kaph, and is thus related to the modern Latin K and Greek Kappa. Several identifiable styles of writing the Brahmi Ka can be found, most associated with a specific set of inscriptions from an artifact or diverse records from an historic period. As the earliest and most geometric style of Brahmi, the letters found on the Edicts of Ashoka and other records from around that time are normally the reference form for Brahmi letters, with vowel marks not attested until later forms of Brahmi back-formed to match the geometric writing style.

The Tocharian letteris derived from the Brahmi , and has an alternate Fremdzeichen formused in conjuncts and as an alternate representation of Kä.

The Kharoshthi letter is generally accepted as being derived from the Aramaic Kaph, and is thus related to K and Kappa, in addition to the Brahmi ka.