Estimating unknown quantities is an important task that we are repeatedly confronted with in our everyday lives (e.g., costs of groceries). Often, we have to estimate quantities that range in the hundred-thousands to billions (e.g., property prices, governmental budgets)—although we have only little practical experience in this range. Which psychological factors are involved in accurately estimating quantities in such high ranges? To date, research on real-world estimation has mainly focused on the role of domain knowledge (Brown, 2002; Brown & Siegler, 1993); the role of more basic numeric abilities, such as numeric representation—which has been shown to contribute to performance in numeric memory and preferential choice (Peters & Bjalkebring, 2015; Schley & Peters, 2014)—has not been investigated yet. To examine the extent to which basic numeric representation (i.e., the ability to accurately map quantities of different magnitudes in relation to each other) is associated with real-world estimation of large numbers, we conducted an online study with N = 284 participants. They first estimated the populations of 32 countries; then they completed a number line task, in which they had to indicate where a number is located on a line (Siegler & Opfer, 2003). The results indicated that a higher estimation accuracy of country populations was indeed associated with higher accuracy in the number line task. Thus, we show for the first time that real-world estimation of large numbers taps into basic numeric representation. The results might help design interventions to improve real-world estimations for large numbers.