sriyadh,
Welcome to PPRuNe.
I agree with glendalegoon. Calculate how long it will take you to descend to circuit altitude at 500 fpm and then calculate the distance required, using your descent TAS (ignore the descent angle - it is small).
For most light aircraft that I fly, I assume two nm per minute. So for a 500 fpm descent, I use four nm per 1000' of height loss.