Background “Depth of invasion” is an additional index incorporated in 8th AJCC staging system for oral cavity squamous cell carcinoma based on its prognostic significance. Pre‐operative assessment by clinical palpation and imaging modalities has been used with limitations. The aim of the study is to compare different techniques including clinical palpation, ultrasound, and magnetic resonance imaging with histopathology for assessment of depth of tumor invasion. Materials Fifty patients of carcinoma tongue (T1–T3) were enrolled. Clinical palpation, Ultrasound tongue, and Magnetic resonance imaging were used to assess depth of tumor invasion. Microscopic depth of invasion was considered as reference. Statistical analysis was done to assess the level of agreement, reliability, and internal consistency. ROC analysis was done to find the “Area Under Curve” for microscopic depth versus ultrasound, MRI, and gross histopathological “depth of invasion”. Results Ultrasound tongue showed highest “area under curve”, Intra class correlation (ICC:0.786) with a good consistency (Cronbach's Alpha:0.880) with histological reference compared to MRI(ICC:0.689;CA:0.816). Clinical palpation showed weak agreement (Kappa:0.43) for assessing depth. To observe the concordance between ultrasound and microscopic depth, Lin's Concordance Correlation Coefficient (CCC = 0.782) was calculated with 95% limits of agreement. Lin's concordance correlation between ultrasound and microscopic depth showed a good agreement. Conclusions Ultrasound tongue is a reliable imaging modality for pre‐operative T staging by assessing tumor “depth of invasion” in carcinoma tongue patients with good internal consistency as per 8th AJCC staging system. Level of Evidence 2 (CEBM‐Level of Evidence‐2.1) Laryngoscope, 134:215–221, 2024 Depth of invasion is new parameter add in 8th AJCC staging system for Oral cavity squamous cell carcinoma in clinical T staging. Accurate assessment is paramount for both staging and prognostication. Our study showed USG tongue is reproducible and reliable method which is quick, repeatable before surgery and cost‐effective.