Sound pressure is the measurand of acoustic quantity. Acoustic instruments are used to determine the quantity value of sound pressure. Calibration of the instrument is required to ensure the accuracy of the measurement results. The metrological traceability linked the instrument measurement result to the primary standard through an unbroken calibration chain by the secondary lab to the National Metrology Institute. This chapter overviews acoustical measurement instruments such as microphones, acoustic calibrators, and sound level meters. The working principles of these instruments and their calibration procedures, aligned with the applicable IEC standards, will be briefly explained.