<p>This study examined junior high school, high school, and university students’ understanding of uncertainty in scientific measurement, by administering a paper-pencil or online test. The participants were 285 students from junior high schools, 137 students from high schools, and 250 students from universities. The results were as follows: overall, statistically significant differences between test scores by students from different school types were found. High school and university students had higher scores than junior high school students. The high school students studying physics, which was used as the context of the test, had higher scores than other high school students. The university students’ test scores were not affected by their fields of specialization. Students from all types of schools did not realize that uncertainty will inevitably occur in scientific measurement. Compared to the older students, junior high school students had less knowledge of the uncertainty caused by human and instrumental factors. Regarding instrumental factors, the students were asked for their preference between analog and digital measuring tools. Some students selected an analog thermometer because of its readability, operationality, and continuous measurement, while others naively selected a digital one because they considered it to be more accurate due to its technological aspect. At least about 60% of the students selected the mean value as the representative value for a set of data and could calculate a reference value in other measurements. The students from all school types had difficulties in evaluating scientific measurement by considering accuracy and precision together. They considered a set of data in which the values were near each other as consistently acceptable data. This indicated that it is easier for them to understand the idea of precision in scientific measurement compared to the idea of accuracy. The findings of the study suggested a need for further research on the relationship between students’ understanding of the uncertainty in scientific measurement with related knowledge, such as science content knowledge, as well as a need for the development of topics in the science curriculum to enhance students’ understanding of it.</p>