metre per second

metre per second

SI coherent derived unit
Name Symbol Derived quantity
metre per second m s−1 speed,


The metre per second, symbol m s−1, is the SI coherent derived unit of speed (scalar quantity) and velocity (vector quantity).
An object with a constant speed of one metre per second moves a distance of one metre in one second.

The fixed numerical value of the speed of light in vacuum, c, is defined as 299 792 458 when expressed in the unit m s−1.

c \mspace{6mu} = 299 \mspace{4mu} 792 \mspace{4mu} 458 \mspace{6mu} \text{m} \mspace{6mu} \text{s}{^{-1}}

Inverting this relation gives an exact expression for the metre per second in terms of the SI defining constant c :

1 \mspace{6mu} \text{m} \mspace{6mu} \text{s}{^{-1}} \mspace{6mu} = \dfrac{c}{299 \mspace{4mu} 792  \mspace{4mu} 458}

The effect of this definition is that one metre per second is exactly 1299 792 458 of the speed of light in vacuum.


The velocity of an object is the rate of change of its position with respect to a frame of reference, and is a function of time.

Velocity is a vector quantity; both magnitude and direction are needed to define it.


The speed of an object is the magnitude of its velocity. Speed is a scalar quantity.

Using SI coherent units,

v = \dfrac{d}{t}


  • v is the speed in metres per second, symbol m s-1,
  • d is the distance travelled in metres, symbol m,
  • t is the travel time in second, symbol s.

At a constant speed, an object travelling a distance of one metre in a time of one second, has a speed of 1 m s-1.

1 \ \text{m s}{^{-1}} = \dfrac{1 \ \text{m}}{1 \ \text{s}}