Background: Several studies have been performed that compare the accuracy of Robotic-Assisted Total Knee Arthroplasty (RATKA) to conventional instrumentation as well as Computer Assisted Surgery (CAS) to conventional instrumentation, yet there is a lack of studies comparing RATKA to CAS. The purpose of this study is to evaluate the accuracy of a contemporary image free CAS system for TKA in a cadaveric study using the same methodology as used previously to access the accuracy of a RATKA system and Conventional instrumentation. Methods: Four orthopaedic surgeons performed bi-lateral TKA on 18 pelvis-to-toe cadaveric specimens without implantation using the BrainLab Knee3 CAS system. Pre-operative and post-operative computed tomography scans were taken to access the resection accuracy of the CAS system relative to alignment targets recorded intraoperatively. Results: The mean error in femoral coronal angle was 1.08°±0.87° compared to 1.39°±0.95° conventional and 0.63°±0.50° RATKA; the differences between CAS and RATKA were statistically significant. The mean error in the tibial coronal angle was 1.24°±1.13° compared to 1.65°±1.29° conventional and 0.93°±0.72° RATKA. The mean error in femoral flexion was 2.13°±1.87° compared to 3.27°±2.51° conventional and 1.21°±0.90° RATKA; the differences between CAS and manual and CAS and RATKA were statistically significant. The mean errors in the femoral rotation (CAS 1.30°±1.38°, conventional 1.00°±0.70°, RATKA 1.04°±0.81°) and tibial slope (CAS 1.89°±1.28°, conventional 1.63°±1.39°, RATKA 1.62°±1.13°) were similar between the groups. Conclusion: This study showed that for some metrics CAS improves resection accuracy compared to conventional instrumentation and RATKA further improves resection accuracy compared to CAS.