Diagnostic tests for students entering pharmacy degree programmes are usually written tests; however, these may not always give an accurate reflection of students’ ability to deal with simple problems that test basic numerical skills in a defined period of time. An MS PowerPoint-based test comprising 30 questions presented in a timed sequence was developed. The questions ranged from simple multiplication to more complex problems involving calculations of concentration and were presented to first year pharmacy undergraduates at two institutions. The results showed that although the majority of the students from both institutions were able to answer simple arithmetic questions correctly, they performed less well on questions involving fractions, powers of ten, multistep calculations and calculations of concentration from text-based problems. This test highlights the types of problems students find difficult to solve and, serves as a useful diagnostic tool enabling a more targeted approach to teaching.