Aim: This study was undertaken with an objective to find out the accuracy and reliability of presurgical ridge mapping (RM) on a diagnostic cast for linear measurements in the horizontal direction on cone-beam computed tomography (CBCT) and direct surgical assessment. Materials and methods: In total, 25 patients based on inclusion and exclusion criteria were selected. An acrylic stent with two points marked at 3 mm and 6 mm from the soft tissue summit of the alveolar ridge was fabricated. Linear measurements at these points were estimated with three techniques viz. RM on the diagnostic cast, CBCT, and direct surgical in situ measurements after flap reflection. Results: Considering direct in situ surgical measurements as the gold standard with an accuracy of 100%, the accuracy for CBCT and RM on the diagnostic cast was 95.5% and 87.4%, respectively, for the maxillary arch. Whereas the accuracy for CBCT and RM on the diagnostic cast was 88.6% and 92.2%, respectively, for mandibular arch. Conclusion: The three approaches discussed are reliable for the assessment of ridge dimensions in the horizontal direction. Ridge mapping on the diagnostic cast is a simple, precise, noninvasive technique without any radiographic exposure. Clinical significance: Ridge mapping on a diagnostic cast along with two-dimensional (2D) radiography can be used as a valuable chairside diagnostic tool in the treatment planning prior to dental implant placement in the cases of a regular alveolar ridge and even mucosal lining. This clinical technique provides zero radiation exposure and is also cost-effective.