Hell will be full of sinners, heaven will be full of sinners saved by God's grace.
Luke 9:46 There arose an argument among them about which of them was the greatest. 9:47 Jesus, perceiving the reasoning of their hearts, took a little child, and set him by his side, 9:48 and said to them, “Whoever receives this little child in my name receives me. Whoever receives me receives him who sent me. For whoever is least among you all, this one will be great.”