Background: Maintaining balance is important throughout life. The Nintendo Wii Balance Board (WBB) can give reliable quantitative measures of postural balance, but reference data are lacking. Furthermore, one-leg standing balance across the adult lifespan is not fully described. The aim of the study was (1) to provide reference data on postural balance in multiple standing positions using a WBB, (2) to determine an age cut-off for the ability to stand on one-leg in men and women. Methods: This was a cross-sectional study and data was collected in two cities in Denmark (Aalborg and Odense) and Norway (Oslo and Ålesund) during spring and summer of 2016. Postural balance was assessed in individuals across the adult lifespan in three different bases of support positions (hip-wide and narrow two-legged stance, and one-legged stance) using a WBB. Reference data were analyzed and presented in 10-year intervals. Results: A total of 354 individuals aged 20–99 years were recruited. Reference data were presented in percentiles stratified by gender for the following age categories: 20–29, 30–39, 40–49, 50–59, 60–69, 70–79, and 80+. Data showed that the difference between men and women's balance was larger at older age with men performing worst. The cut-off ability to stand on one-leg was 72.5 years without statistical evidence of gender difference. Conclusion: This study reports reference data for postural balance across the entire adult lifespan using a WBB. More than half of the individuals over 72.5 years of age were unable to stand balanced on one-leg.