The aim of this study are to examine the relationship between prospective classroom teachers' estimation skills based on calculation and their number sense and to investigate whether their number sense and estimation skills change according to their class level and gender. The participants of the study are 125 prospective classroom teachers studying at faculty of education, department of classroom teaching, in a state university in Turkey. The findings of the study revealed that prospective teachers have a low level of scores in terms of number sense and estimation skills, the scores do not change according to gender but there is a statistically significant difference in terms of their grade levels in number sense test. Additionally, it wasn't indicated that there is a statistically significant difference between prospective teachers' number sense and estimation skills scores.