CALCULATION AND PREPARATION OF BUFFER SOLUTIONS: COMPLETE GUIDE USING THE SOFTWARE PEAKMASTER®. Buffers are a widely used resource to keep solutions from abruptly change their pH when amounts of acids or bases are added or when dilution occurs. Considering this, buffer is a topic addressed in several university majors and due its relevance should be well known by students and by all professionals who eventually need to prepared a buffer. Mistakes during the procedure might bring unwanted effects depending on the purpose of the buffer. Even though the theory behind buffers is extensively covered in textbooks, the calculations required can sometimes be interpreted as difficult. Therefore, the aim of this work is to disseminate a tool to assist on these calculations. We provide a practical guide on how to prepare buffers of the user’s choice with or without ionic strength adjustment. Exploring the free software PeakMaster®, the user can calculate pH, ionic strength, buffer capacity and predict the precise concentration of each component involved to the proper preparation of the most common and several others buffer solutions. In addition, we hope this paper can be helpful for anyone who is interested in acquire deeper knowledge about buffers.