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BACKGROUND Ileal pouch anal anastomosis aims to restore continence to patients following total proctocolectomy. However, some patients have inadequate small bowel mesenteric length to achieve reconstruction. No preoperative risk stratification tools of native anatomy exist. OBJECTIVE We report computed tomography-guided measurements of anatomic landmarks to predict non-reach prior to ileal pouch anal anastomosis. DESIGN This is a single institution retrospective analysis of a prospective database. SETTING This study was conducted at Cedars-Sinai between January 2007 and December 2021. PATIENTS Inflammatory bowel disease patients undergoing a 2 or 3-stage ileal pouch anal anastomosis with a preoperative abdominal computed tomography using either an enterography protocol or IV contrast sufficient to visualize mesenteric vasculature. Computed tomography mesenteric indices were assessed including total length (representing length required for the pouch to reach the anal canal), mesenteric length (inherent length of small bowel mesentery) and mobilization length (the difference between total length and mesenteric length). MAIN OUTCOME MEASURES The primary outcome was ileal pouch anal anastomosis non-reach. Secondary outcomes were association of clinical variables and computed tomography mesenteric indices. RESULTS Six of 59 (10%) patients experienced non-reach. Mobilization length was longer in the non-reach group by 5.8 cm (p = 0.01), and mesenteric length was shorter by 3.5 cm (p = 0.04). Mobilization length ≥ 17 cm provided 100% sensitivity and 69% specificity (OR 1.46, AUC 0.84, p = 0.004) for non-reach. Similarly, a mesenteric length < 14.6 cm demonstrated a 100% sensitivity and 49% specificity for ileal pouch anal anastomosis non-reach (AUC 0.75, p = 0.03). LIMITATIONS The retrospective nature of the study precluded a standardized imaging protocol. External validation will be required due to small sample size. CONCLUSIONS Computed tomography-based measurements of length, specifically mesenteric and mobilization length, predict non-reach prior to ileal pouch anal anastomosis. This method is noninvasive, readily available and may be useful for preoperative patient counseling and operative planning. See Video Abstract at http://links.lww.com/DCR/C140.