In order to minimize the risk of infection during the Covid-19 pandemic, peopleare recommended to keep interpersonal distance (e.g., 1 m, 2 m, 6 feet), washtheir hands frequently, limit social contacts and sometimes to wear a face mask.We investigated how people judge the protective effect of interpersonal distanceagainst the Corona virus. The REM model, based on earlier empirical studies,describes how a person’s virus exposure decreases with the square of thedistance to another person emitting a virus in a face to face situation. In acomparison with model predictions, most participants underestimated theprotective effect of moving further away from another person. Correspondingly,most participants were not aware of how much their exposure would increase ifthey moved closer to the other person. Spectral analysis of judgments showedthat a linear ratio model with the independent variable = (initialdistance)/(distance to which a person moves) was the most frequently usedjudgment rule. It leads to insensitivity to change in exposure compared with theREM model. The present study indicated a need for information about the effectsof keeping interpersonal distance and about the importance of virus carryingaerosols in environments with insufficient air ventilation. Longer conversationsemitting aerosols in a closed environment may lead to ambient concentrations ofaerosols in the air that no distance can compensate for. The results of thestudy are important for risk communications in countries where people do notwear a mask and when authorities consider removal of a recommendation or arequirement to wear a face mask.