Imagine yourself moving to another place, and therefore, you need to pack all of your belongings into moving boxes with some capacity. In the classical bin packing model, you would try to minimize the number of boxes, knowing the exact size of each item you want to pack. In the online bin packing problem, you need to start packing the first item into a box, without knowing what other stuff is upcoming. Both settings are somewhat unrealistic, as you are likely not willing to measure the exact size of all your belongings before packing the first item, but you are not completely clueless about what other stuff you have when you start packing. In this article, we introduce the online bin packing with estimates model, where you start packing with a rough idea about the upcoming item sizes in mind. In this model, an algorithm receives a size estimate for every item in the input list together with an accuracy factor $δ$ in advance. Just as for regular online bin packing the items are then presented iteratively. The actual sizes of the items are allowed to deviate from the size estimate by a factor of $δ$. Once the actual size of an item is revealed the algorithm has to make an irrevocable decision on the question where to place it. This is the first time online bin packing is studied under this model. This article has three main results: First, no algorithm can achieve a competitive ratio of less than $\frac{4}{3}$, even for an arbitrary small factor $δ>0$. Second, we present an algorithm that is $1.5$-competitive for all $δ\leq \frac{1}{35}$. Finally, we design a strategy that yields a competitive ratio of $\frac{4}{3}$ under the assumption that not more than two items can be placed in the same bin, which is best possible in this setting.