Abstract Background Both universal goniometer and electro-goniometer are used for measuring joint range of motion in physiotherapy. Active knee extension test is a way to assess hamstring shortness in patients with chronic low back pain. The aim of this study was to assess universal goniometer and electro-goniometer reliability in measuring knee angle during active knee extension test. Methods This was an intra-examiner reliability study between three measurements of knee extension angle that conducted on 45 patients with chronic low back pain having short hamstring muscle that referring to Kermanshah University of Medical Sciences clinic from 2016 to 2017. Knee extension angle was measured three times during active knee extension test with both universal goniometer and electro-goniometer. The measurement of knee extension angle was done at the beginning, middle and the end of one single session by one experienced physiotherapist. The intra-class correlation coefficient (ICC) and standard error of measurements (SEM) were used to quantify intra-examiner reliability. Results For both methods, the reliability test values were found to be greater than 0.7 in the range of 0.92 to 0.99 (CI 95% ranged over = 0.94 to 0.99), which are classified as good reliability. The SEMs ranged from 1.04° to 2.16° for both scales. Conclusion Universal goniometer in clinical evaluations of patients (as they are easy to be employed) and electro-goniometer in laboratory studies (as they are more accurate) are reliable.