"Therefore, as one trespass led to condemnation for all men, so one act of righteousness leads to justification and life for all men. 19 For as by the one man's disobedience the many were made sinners, so by the one man's obedience the many will be made righteous. 20 Now the law came in to increase the trespass, but where sin increased,grace abounded all the more, 21 so that, as sin reigned in death, grace also might reign through righteousness leading to eternal life through Jesus Christ our Lord." - Romans 5:18-21
How many sins does it take to become a sinner? None.
We were once called sinners not because we committed a sinful act but because we were born into the bloodline of Adam. Through one man's sin, all who would be born upon the Earth would possess the same nature as their forefather, a nature prone to sin. It was not what we did that made us unrighteous but who we were. Birth always determines identity. You are given your father's last name and it is His blood that pulses through your veins. You didn't become a part of your family by mimicking their actions and gestures, rather you were born with their DNA, and just as you did nothing to receive their genetic code, so you can do nothing to change it.
How many good deeds does it take to become righteous? None.
We have been made righteous not because we did any amount of good deeds but because we were born again into the bloodline of Christ, the last Adam. Through one man's life of righteousness, holiness has been imputed to all who simply believe that he died for us, and with us, so that he could ascend to the Father carrying us in Him. Birth always determines identity. We were not adopted into the family of God by trying to mimic the life of Jesus and climb the ladder of the law hoping to someday make it up to heaven, but by our simple faith in Christ's accomplishment's on our behalf, he gave us his DNA, for we died with him, a death to the nature of Adam, and were raised with him to a life of righteousness. We did nothing to deserve this, nor can we do anything to change this.
Now that's amazing grace.