ICH Volume Calculator
Estimate the volume of an intracerebral hemorrhage (ICH) from three CT measurements using the validated ABC/2 ellipsoid method. Enter the longest diameter (A), the perpendicular width (B), and the craniocaudal height (C) from your CT scan. For irregular, separated, or multinodular bleeds, switch to ABC/3. Results update instantly with a severity tier and a worked example of the calculation.
Formula
Worked example
A patient has a right putaminal hemorrhage measuring A = 4.0 cm, B = 3.0 cm, C = 3.0 cm on CT. The bleed is ellipsoid so we use ABC/2: (4.0 x 3.0 x 3.0) / 2 = 36 / 2 = 18 mL. This falls in the moderate category and is below the 30 mL ICH Score threshold.
What is the ABC/2 method for ICH volume?
The ABC/2 formula estimates the volume of an intracerebral hemorrhage from three orthogonal CT dimensions: A (the longest diameter on the axial slice with the most hemorrhage), B (the width perpendicular to A on the same slice), and C (the craniocaudal height of the bleed). The product of the three dimensions divided by 2 approximates the volume of an ellipsoid. The method was validated by Kothari and colleagues in 1996 against the planimetric gold standard and shows an R-squared of 0.96 with an intraclass correlation of 0.99, meaning it is accurate to within about 1-2 mL for most bleeds. The main limitation is that it overestimates volume for irregular, separated, or multinodular hemorrhages, which is why those shapes use a divider of 3 (ABC/3) instead.
How to measure A, B, and C on CT
Scroll through the axial CT stack and find the slice where the hemorrhage area appears largest. On that slice, draw the longest straight line through the hematoma - this is A. Then draw a second line through the same slice that is perpendicular (90 degrees) to the first line and passes through the widest point of the hematoma - this is B. For C, either measure the craniocaudal span directly by counting from the lowest to the highest axial slice containing hemorrhage (multiply the number of qualifying slices by the slice thickness), or use a coronal or sagittal reconstruction to read C directly. When counting slices, weight each by hemorrhage area: a slice with more than 75% of its area occupied by hemorrhage counts as 1, one with 25-75% counts as 0.5, and one with less than 25% counts as 0. This weighting corrects for the tapering shape at the poles of the hematoma.
Clinical significance of ICH volume
Hematoma volume is one of the strongest independent predictors of 30-day mortality and long-term functional outcome after intracerebral hemorrhage. The ICH Score (Hemphill 2001) - a widely used bedside prognostic tool - awards one point for a volume of 30 mL or more. Volumes above 60 mL are associated with mortality rates exceeding 70% at 30 days. Beyond its prognostic role, volume guides triage: large hematomas near the surface may be candidates for surgical evacuation, while deep basal-ganglia bleeds of any size are generally managed medically. Hematoma expansion occurs in roughly 30-40% of patients within the first 24 hours and roughly doubles the risk of death or poor outcome, making early accurate volume estimation critical for treatment decisions.
ABC/2 versus ABC/3: when to use each
The standard ABC/2 formula assumes the hematoma is roughly ellipsoid in shape. When a bleed is clearly irregular (multi-lobed, separated into two or more distinct components, or multinodular with a heterogeneous boundary), the ellipsoid assumption breaks down and ABC/2 systematically overestimates volume. Switching the divider from 2 to 3 reduces that overestimation and brings the estimate closer to planimetric measurements. As a rule of thumb, use ABC/2 for round or oval bleeds without obvious lobulation, and ABC/3 when the hematoma boundary is clearly non-ellipsoid. If you are uncertain, ABC/2 gives a conservative upper bound that is clinically safer than underestimating.
ICH Volume severity tiers and clinical thresholds
| Volume range | Category | 30-day mortality (approx.) | ICH Score (volume component) |
|---|---|---|---|
| < 10 mL | Small | < 10% | 0 points |
| 10-29 mL | Moderate | 10-20% | 0 points |
| 30-59 mL | Large | 25-45% | 1 point |
| >= 60 mL | Very Large | > 70% | 1 point |
Volume categories used in clinical practice and outcome research. The 30 mL threshold forms part of the ICH Score (Hemphill 2001). Mortality estimates are approximate 30-day figures from published ICH cohort studies.
Frequently asked questions
How accurate is the ABC/2 method?
Very accurate for ellipsoid bleeds. Against the planimetric gold standard (manual slice-by-slice tracing), the ABC/2 formula has an R-squared of 0.96 and an intraclass correlation of 0.99. The mean overestimation is about 1.5 mL. Accuracy drops for highly irregular or multinodular hemorrhages, which is why those shapes are calculated with ABC/3.
What are the units - mL or cm^3?
For clinical purposes 1 mL and 1 cm^3 are identical (1 cubic centimetre equals 1 millilitre). The calculator shows both but they are numerically the same. CT measurements are usually in millimetres on the workstation, so make sure to convert to centimetres before applying the formula (divide by 10).
What is the 30 mL clinical threshold?
The 30 mL threshold is one component of the ICH Score developed by Hemphill and colleagues in 2001. An ICH volume of 30 mL or more contributes one point to the score, which predicts 30-day mortality. Volumes at or above 30 mL are also used by many centres as a relative threshold for neurosurgical consultation, though evidence for surgical benefit depends heavily on hematoma location and patient factors.
How do I weight the slices for counting C?
Count each axial CT slice that contains hemorrhage, weighting by the proportion of the slice area occupied by blood: slices with 75% or more hemorrhage area count as 1 full slice, slices with 25-75% area count as 0.5 slices, and slices with less than 25% count as 0 (they are excluded). Multiply the weighted total by the slice thickness in millimetres to get C in millimetres. For example, 4 full slices plus 2 half-slices at 5 mm thickness: (4 + 1) x 5 = 25 mm.
Can this calculator be used for subdural or subarachnoid hemorrhage?
The ABC/2 method was validated for intraparenchymal (intracerebral) hemorrhage. For subdural hematomas, which are crescent-shaped rather than ellipsoid, the formula tends to underestimate volume significantly and a different approach (such as a modified ellipsoid or planimetric method) is preferable. For subarachnoid hemorrhage, volume is rarely measured and the Fisher scale or modified Fisher scale uses qualitative imaging criteria instead.