<b><i>Background and Purpose:</i></b> Hematoma volume is a key determinant of outcome in acute intracerebral hemorrhage (ICH). We aimed to compare estimates of ICH volume between simple (ABC/2, length, width, and height) and gold standard planimetric software approaches. <b><i>Methods:</i></b> Data are from the second Intensive Blood Pressure Reduction in Acute Cerebral Hemorrhage Trial (INTERACT2). Multivariable linear regression was used to compare ICH volumes on baseline CT scans using the ABC/2, modified ABC/2 (mABC/2), and MIStar software. Other aspects of ICH morphology examined included location, irregularity, heterogeneity, intraventricular and subarachnoid hemorrhage extension (SAH) of hematoma, and associated white matter lesions and brain atrophy.<b><i> Results:</i></b> In 2,084 patients with manual and semiautomated measurements, median (IQR) ICH volumes for each approach were: ABC/2 11.1 (5.11–20.88 mL), mABC/2 7.8 (3.88–14.11 mL), and MIStar 10.7 (5.59–18.66 mL). Median differences between ABC/2 and MIStar, and mABC/2 and MIStar were 0.34 (–1.01 to 2.96) and –2.4 (–4.95 to –0.7416), respectively. Hematoma volumes differed significantly with irregular shape (ABC/2 and MIStar, <i>p</i> &#x3c; 0.001; mABC/2 and MIStar, <i>p</i> = 0.007) and larger volumes (mABC/2 and MIStar, <i>p</i> &#x3c; 0.001; ABC/2 and MIStar, <i>p</i> = 0.07). ICH with SAH showed a significant discrepancy between ABC/2 and MIStar (<i>p</i> &#x3c; 0.001).<b><i> Conclusions:</i></b> Overall, ABC/2 performs better than mABC/2 in estimating ICH volume. The largest discrepancies were evidenced against automated software for irregular-shaped and large ICH with SAH, but the clinical significance of this is uncertain.