Otta may refer to:

• A working name leading to what became the SI prefix for 10²⁴. It apparently came from the Greek κτώ, eight, because it was equal to 1000⁸. It had been informally introduced before 1991, date at which the real prefix, yotta, a deliberate variant largely chosen due to considerations of the symbol to use for it, was promulgated. See non-SI unit prefix.

• In Norse mythology, Otta the Simple was Freya's lover.
• Otta, Norway, a Norwegian town in Gudbrandsdal
• The Otta River in Norway.
• An alternative spelling of Ota, Nigeria, a city in Ogun State, Nigeria, private residence of Nigerian President Olusegun Obasanjo
• An Indian weapon, the otta, a curved stick used in the Kalarippayattu martial art.