The utility model discloses a ring groove synthesizes size measuring tool, including the bottom plate, set up in on the bottom plate and be used for the installation await measuring the piston the positioning disk, set up in first support frame on the bottom plate, set up in a plurality of head measuring sensor to being used for detecting the end footpath of each the rectangle annular on the piston that awaits measuring on the first support frame, and it is right with each head measuring sensor signal connection, be used for according to its treater that detects the diameter of each rectangleannular of data calculation. The utility model discloses a ring groove synthesizes size measuring tool, through set up on the first support frame each to head measuring sensor, the diameter of can thesingle accomplishing each the rectangle annular on the piston that awaits measuring detects, handle calculation to each to head measuring sensor's detection data by the treater again, obtain the diameter data of each rectangle annular, artifical measurement operation has been avoided during this time, thereby the system error who avoids many times manual measurement ring groove to cause amounts to, eliminate the influence of human factor, the measurement precision is improved.