Sectors of Circles A sector of a circle is the region of a circle bounded by two intercepted B 0 A T C and their How large the central angle is in relation to the measure of the entire circle determines how big the sector is in relation to the entire circle. Calculating Area of a Sector The area of a . The . The area of the of a circle is found by multiplying these two factors: of the central angle over 360 degrees circle x Area of a sector = 360 (r) 16 135