Not using offspring diapers but can refer to the baby growth chart for the weight in 50th percentile to estimate the age. Multiply by the frequency of change. For eg, I change my baby once every 3 hours, ie 8 diapers per day * (days in a month till max weight of diaper)
Previously using offspring. Sizes depend on baby. Nb 1 packet switch to S. 3 month old use M tape. Use pants only when travelling. And when baby can stand with support.