Monte Carlo simulations are performed on personal computers to estimate π . RND function of VBA(Visual Basic for Application) in Microsoft Excel® is used for pseudorandom number generation. Mersenne Twister is used for pseudorandom number generation, too. Central limit theorem is adapted to estimate accuracy of Monte Carlo simulations. The limit of frequency of random number generation by RND function is discussed. Monte Carlo simulations are performed on various types of personal computers to check machine time. Personal computers, which are commonly used in class room, will be available for Monte Carlo simulation of π in reasonable machine time in lessons.