Two circles are said to be congruent if they have the same radius.


Congruent circles 
Not congruent circles 
To check whether two given circles C_{1} and C_{2} are congruent or not, trace C_{1} and put it over C_{2} such that, their centres coincide with each other. If the circle C_{1}exactly covers the circle C_{2}, we will see that they have the same radii. We then say that, the two circles are congruent to each other. We will write C_{1} C_{2}.