A disordered respiration pattern can lead to physiological and psychological dysfunctioning. A regulated rate of respiration calms the mind and improves health. This paper proposes a portable, comfortable, and cost-effective solution of using a smartphone to estimate respiration rate with the help of an attached headset microphone placed beneath the nose. The method uses the strength of nasal breath sound to estimate different breathing rates. Inhaling and exhaling periods are estimated by taking the average of the amplitude of nasal breath sound. We evaluated the accuracy of the proposed solution by collecting data from people of different gender, across all age groups, for a varied time duration, using smartphone and microphone of varied configurations and sensitivity respectively. Background noise is inevitable and it distorts the nasal breathing sound, so the accuracy of the technique in different noisy settings is evaluated. The experimental results showed that the technique performed well even in noisy environments. The observed errors are reasonable for non-critical clinical applications, e.g. the error is less than 10% even in noisy environments for a user.