A nanosecond (ns) is a unit of time in the International System of Units (SI) equal to one billionth of a second, that is, 1⁄1 000 000 000 of a second, or 10−9 seconds. The term combines the SI prefix nano- indicating a 1 billionth submultiple of an SI unit (e.g. nanogram, nanometre, etc.) and second, the primary unit of time in the SI. A nanosecond is equal to 1000 picoseconds or 1⁄1000 microsecond. Time units ranging between 10−8 and 10−7 seconds are typically expressed as tens or hundreds of nanoseconds.