OBJECTIVE: To evaluate the accuracy of various prostate tumour volume (TV) estimation methods. To determine the most appropriate estimation method for current clinical practice. PATIENTS AND METHODS: Radical prostatectomy (RP) specimens from multiple institutions were analysed by a single uro-pathologist between September 2009 and May 2011. Tumour properties including thickness, width and length were collected and TV was established using computer-assisted image analysis (CAIA). TV estimation methods including; square, cuboidal and ellipsoidal estimations were calculated using previously reported formulae. The estimation methods were compared against the 'gold-standard' and the accuracy of identifying clinically significant tumours of TV ≥0.5 cc was determined. RESULTS: In all, 299 consecutive specimens were analysed by a single uropathologist. The median index TV on CAIA was 1.42 cc. Of the four estimation methods, the ellipsoid methods produced the closest correlation with the gold-standard (r(2) 0.91, P = 0.71). This correlation lost accuracy when larger tumours (TV >4 cc) were excluded from the analysis (r(2) = 0.73, P = 0.003). Sensitivity and specificity for identifying clinically significant tumours was 94% and 92% respectively, when using the ellipsoid estimation. CONCLUSIONS: In current uro-pathology, the ellipsoidal estimation method appears to be the most suitable for estimating TV in prostate cancers. This method is cheap, reproducible and sensitive and can be safely used as a surrogate for CAIA volumes when such technology is not available.