ICH Volume Calculator (ABC/2)
Estimate intracerebral hemorrhage volume from head-CT measurements with the published ABC/2 method — A × B × C divided by 2. Enter lengths in mm or cm (converted automatically), pick a method variant, and count slices the way radiologists do.
ABC/2 calculator
Fill in the measurements from the CT workstation. The result updates live as you type. 1 cm³ = 1 mL.
Longest line across the bleed on the largest axial slice.
Longest line perpendicular to A, on the same slice.
Count full slices as 1, partial slices as 0.5 (see the half-slice rule below).
From the scan metadata (typically 2.5–10 mm).
Largest superior-to-inferior extent, measured on coronal or sagittal images.
Educational estimate — not medical advice. This number is geometry arithmetic, not a diagnosis. Interpretation requires a qualified clinician with the full clinical picture.
How to measure A, B, and C
The reference method from Kothari et al. (Stroke, 1996), step by step.
- Find the reference slice. Scroll through the axial head-CT series and pick the slice on which the hemorrhage looks largest.
- Measure A. On that slice, draw the longest straight line across the hemorrhage — this is A.
- Measure B. On the same slice, draw the longest line that is perpendicular (90°) to A — this is B.
- Measure C. Count the axial slices that show hemorrhage and multiply by the slice thickness (e.g. 6 slices × 5 mm = 3 cm). Alternatively, measure the largest superior-to-inferior diameter on coronal or sagittal reformats.
- Apply the half-slice rule. Compare each slice to the reference slice: roughly 25–75% of the reference area counts as 0.5 slices; under ~25% does not count; over ~75% counts as a full slice.
The formula
Where the “divide by 2” comes from.
ABC/2 is a simplification of the volume of an ellipsoid. An ellipsoid with diameters A, B, and C has volume:
V = ⅔⁄⅓ × π × (A/2) × (B/2) × (C/2)
Approximating π ≈ 3, the constants cancel to give the bedside formula:
V = (A × B × C) ÷ 2
Because of this derivation, the method implicitly assumes the hemorrhage is roughly ellipsoid. The more the bleed deviates from that shape, the less accurate the estimate — which is why the ABC/3 variant exists for irregular hematomas.
Worked examples
Each row computed with the same engine as the calculator above.
| # | A | B | C | Method | Volume |
|---|---|---|---|---|---|
| 1 | 6.0 cm | 3.0 cm | 6 slices × 5 mm = 3.0 cm | ABC/2 | (6 × 3 × 3) ÷ 2 = 27.0 mL |
| 2 | 45 mm | 32 mm | 10 slices × 5 mm = 5.0 cm | ABC/2 | (4.5 × 3.2 × 5) ÷ 2 = 36.0 mL |
| 3 | 5.0 cm | 4.0 cm | 4.0 cm (direct) | ABC/3 | (5 × 4 × 4) ÷ 3 = 26.67 mL |
Example 2 shows automatic mm→cm conversion: 45 mm = 4.5 cm, 32 mm = 3.2 cm, 50 mm = 5.0 cm.
Limitations
- Shape assumption. ABC/2 assumes an ellipsoid bleed; irregular or multilobed hematomas are systematically overestimated.
- Small bleeds. Precision drops for small volumes because a 1–2 mm measurement error is a large fraction of A or B.
- Not a planimetric measurement. Slice-by-slice segmentation software remains the reference; ABC/2 is a rapid bedside estimate (mean 38 s in the validation study).
- Intraventricular blood. The original validation excluded large ventricular components; blood that has ruptured extensively into the ventricles is not well described by this formula.
Which tool do you need?
This tool estimates brain hemorrhage volume from CT measurements (A, B, C diameters) for education and research arithmetic.
Not this tool: for the volume of geometric 3D shapes (spheres, cylinders, boxes), use our geometry volume calculators instead — different inputs, different math.
Browse the full collection in the tools directory.
References
- Kothari RU, Brott T, Broderick JP, Barsan WG, Sauerbeck LR, Zuccarello M, Khoury J. The ABCs of measuring intracerebral hemorrhage volumes. Stroke. 1996;27(8):1304–1305.
- Huttner HB, et al. Comparison of ABC/2 estimation technique to computer-assisted planimetric analysis in warfarin-related intracerebral parenchymal hemorrhage. Stroke. 2006;37(2):404–408. (ABC/3 for irregular hematomas)
- Hemphill JC 3rd, et al. The ICH Score: a simple, reliable grading scale for intracerebral hemorrhage. Stroke. 2001;32(4):891–897.
Frequently asked questions
What is the ABC/2 method for ICH volume?
The ABC/2 method is a bedside technique for estimating the volume of an intracerebral hemorrhage (ICH) from a head CT scan, validated by Kothari et al. (Stroke, 1996). A is the greatest hemorrhage diameter on the axial slice where the bleed looks largest, B is the largest diameter perpendicular (90 degrees) to A on that same slice, and C is the number of CT slices showing hemorrhage multiplied by the slice thickness. Volume in milliliters equals (A x B x C) / 2 when all three measurements are in centimeters.
How do I measure A, B, and C on a head CT?
First find the axial slice on which the hemorrhage appears largest — this is the reference slice. On that slice, measure A as the longest straight line across the hemorrhage, and B as the longest line that is perpendicular (90 degrees) to A, also on that slice. For C, count the slices that show hemorrhage and multiply by the slice thickness shown in the scan metadata (for example, 6 slices x 5 mm = 3 cm). All measurements must be taken by a qualified clinician using calibrated radiology measurement tools.
How do I count slices when the bleed only partly appears on a slice?
A commonly taught refinement is the half-slice rule: compare each slice to the reference slice (the one used for A). If the hemorrhage area on a slice is roughly 25% to 75% of the area on the reference slice, count it as half a slice (0.5). If it is less than about 25%, do not count it. If it is more than about 75%, count it as a full slice. This calculator accepts fractional slice counts such as 5.5.
Can I enter measurements in millimeters?
Yes. Each length field (A, B, and C or slice thickness) has its own unit selector for millimeters or centimeters, and the calculator converts everything to centimeters automatically. The formula only gives milliliters when A, B, and C are all in centimeters, so entering mixed units without conversion would produce a wrong result — this tool handles the conversion for you.
What is the difference between ABC/2, ABC/2.3, and ABC/3?
ABC/2 is the standard formula validated by Kothari et al. (1996). ABC/2.3 is an adjusted variant some clinicians use to slightly reduce the known tendency of ABC/2 to overestimate volume. ABC/3 was suggested for irregularly shaped hematomas — for example those related to anticoagulant therapy — where ABC/2 overestimates substantially (Huttner et al., Stroke, 2006). Choose the method a qualified clinician considers appropriate for the case; this tool does not recommend one.
Why does the formula divide by 2?
ABC/2 is a simplification of the volume formula for an ellipsoid. An ellipsoid with diameters A, B, and C has volume (4/3) x pi x (A/2) x (B/2) x (C/2). Approximating pi as 3, this simplifies to (A x B x C) / 2. So the method implicitly assumes the hemorrhage is roughly ellipsoid in shape — the more irregular the bleed, the less accurate the estimate.
How accurate is the ABC/2 estimate?
In the original validation study of 118 patients, ABC/2 estimates took an average of 38 seconds and correlated with computer-assisted planimetric measurement with R-squared = 0.96, and inter- and intra-rater reliability were excellent (intraclass correlation 0.99). Accuracy is best for round-to-ellipsoid hematomas; the method overestimates irregular hematomas and is less precise for small volumes. It is an estimate, not a precise measurement.
What does a result of 30 mL mean?
By itself, a number from this tool means nothing about a patient's condition. As a point of published context only: the ICH Score (Hemphill et al., Stroke, 2001), a research grading scale, uses an ICH volume of 30 cm3 or more as one of its five scoring parameters. Interpreting any volume value requires a qualified clinician with the full clinical picture — this tool does not diagnose, predict outcomes, or recommend treatment.
Can this calculator be used for epidural, subdural, or subarachnoid bleeds?
The ABC/2 formula is geometry, so it can produce a number for any roughly ellipsoid collection of blood, and clinicians sometimes apply it to other hematoma types. However, it was validated specifically for spontaneous intracerebral hemorrhage. Other bleed types have different shapes and clinical meanings, and dedicated assessment criteria exist for them. Do not assume an estimate for another bleed type carries the same validity.
Is this medical advice?
No. This is an educational calculator that performs the arithmetic of a published formula. It is not medical advice, does not diagnose any condition, does not predict any outcome, and must not guide treatment decisions. Measurements must be made and interpreted by a qualified clinician. If you are dealing with a real medical situation, seek professional medical care.
Free tool by NRTechStudio