What is the length of 1 second in meters If time is treated as a fourth dimension of spacetime, what is relation between length and time units?
Or in other words, how can I convert time units to length units, for instance seconds to meters?
 A: In special theory, the space time geometry contains 4 dimensions (3 space + 1 time) which look like $(x, y, z, ct)$. The distance between two points in this space is not given by the usual euclidean geometry $$d_{12}=\sqrt{(x_1-x_2)^2+(y_1-y_2)^2+(z_1-z_2)^2+c^2(t_1-t_2)^2}$$ rather is given by $$d_{12}=\sqrt{(x_1-x_2)^2+(y_1-y_2)^2+(z_1-z_2)^2-c^2(t_1-t_2)^2}$$ 
This space is called a Minkowski space. This is the relation between length and time. 
I feel that as such you can not define a relation between to convert time units to length units. I think Prathyush has assumed $d_{12}=0$ and ${(x_1-x_2)^2+(y_1-y_2)^2+(z_1-z_2)^2}=1$ 
A: Prathyush's answer is the most useful one, but time is just another dimension -- you could use any units you like, same as the other dimensions. For example another useful unit is $c$ itself.
A: The length of one second in meters is the distance travelled by light in one second. 
$1\ \mathrm s=c\times1\ \mathrm s= 299\,792\,458\ \mathrm m$
The reason we use the same units for time and distance is special relativity, whose foundation rests on the speed of light (in vacuum) being constant in all inertial frames of reference. Its universality allows us to use the same units for both time and distance.
