- prefix one quadrillion, 1015.
(written as peta)one quadrillion (250).
- A metric prefix representing 1015, which is equal to a quadrillion. For instance, 1 petahertz is equal to 1015 Hz, or 1,000,000,000,000,000 Hz. When referring to binary quantities, such as bits and bytes, it is equal to 2, or 1,125,899,906,842,624, although this is frequently rounded to 1,000,000,000,000,000. To avoid any confusion, the prefix pebi- may be used when dealing with binary quantities. Its abbreviation is P.