For liability to arise in Dutch tort law, there must be an unlawful act which can be imputed to the injurer (art. 6 : 162 para. 1 new BW). Conduct is unlawful if it infringes a subjective right, violates a statutory duty or an unwritten rule on proper social conduct (para. 2). Because this last ground for liability has been formulated in such vague and broad terms it provides judges the possibility to hold an injurer liable in all cases where an injurer’s behaviour is improper according to prevailing opinions in society. The question rises how judges fill in this vague norm. In other words, what elements are taken into consideration when they regard behaviour as improper. In the United States judge Learned Hand formulated a rule of thumb to distinguish proper from improper behaviour already more than fifty years ago in the case United States v. Carroll Towing. This rule was later acknowledged by legal scholars as a good description of how American judges determine negligence and has been heralded by law and economics scholars as a simplified way to find the optimal amount of care. In this article we illustrate that Dutch judges also (implicitly) apply the Learned Hand formula.