So you have a LARGE backlog and you have decided that you need to estimate it. You can do larger scale estimation in MANY ways. What Mathias Holmgren will share with you here is just one way he have found to do it effectively, with enough accuracy at a reasonable cost. It requires some pre-conditions, such as having a team with an established way of working and some way of estimating on the team level, so it may not fit your situation. But if it does it is probably worth your time to check out. Read more about Bucket Estimation here.