ICH Volume Calculator (ABC/2 intracerebral haemorrhage volume from CT)

Understanding the ICH volume calculator (ABC/2) — concept and principle

This calculator estimates the volume of an intracerebral haemorrhage (a bleed inside the brain) from three measurements on a CT scan, using the ABC/2 method of Kothari and colleagues. Clinicians use the volume for prognostic scores such as the ICH score and to follow whether a bleed is growing.

ABC ÷ 2: with the default inputs the result is 18 mL (4 × 3 × 3 ÷ 2 (ellipsoid 18.8)).

How it is calculated

C (cm) = number of CT slices showing the bleed × slice thickness (mm) ÷ 10

Volume (mL) = A × B × C ÷ 2

Exact ellipsoid volume = π ÷ 6 × A × B × C

A is the largest diameter of the bleed on the slice where it is biggest (cm).
B is the diameter at 90° to A on the same slice (cm).
Count a slice as half if the bleed there is about 25–75% of its largest area, and leave out slices where it is much smaller.
1 cm³ = 1 mL.

The principle

Many brain bleeds are roughly ellipsoid. The volume of an ellipsoid with diameters A, B and C is π/6 × A × B × C, and π/6 is 0.52, very close to one half. Using ÷ 2 makes the calculation easy at the bedside. Kothari and colleagues showed that this quick estimate correlated closely with computer volume measurements.

Worked example

Default inputs: A 4 cm, B 3 cm, 6 slices of 5 mm.

C = 6 × 5 ÷ 10 = 3 cm.
ABC/2 = 4 × 3 × 3 ÷ 2 = 18 mL.
Ellipsoid = 0.5236 × 36 = 18.8 mL.

Each point is the calculator re-run with only “A — largest bleed diameter on the slice where it is biggest (cm)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

A — largest bleed diameter on the slice where it is biggest (cm)	Haematoma volume, ABC/2 (mL)
1	4.5
2	9
3	13.5
4	18
5	22.5
6	27
8	36

How to read the result

Where does your result fall?

A volume of 30 mL or more adds a point to the ICH score and is linked to a worse outcome; very large bleeds carry high mortality. Growth of the bleed on repeat CT is also important. ABC/2 tends to overestimate irregular or lobulated bleeds and those in people taking blood thinners.

Common mistakes

Measuring A and B on different slices.
Counting every slice with any blood as a full slice.
Forgetting to convert slice thickness from mm to cm.

Keep in mind: This is a measurement aid for clinicians, not a diagnosis. Imaging must be read by a qualified radiologist or clinician.

Frequently asked questions

Why divide by 2?

Because the ellipsoid factor π/6 ≈ 0.52 is close to one half.

Is ABC/2 accurate?

It is close for regular, oval bleeds and less accurate for irregular shapes.

Can it be used for other bleeds?

Variants are used for other collections, but this version was validated for intracerebral haemorrhage.

Sources: Kothari RU, Brott T, Broderick JP, et al., "The ABCs of measuring intracerebral hemorrhage volumes", Stroke 1996;27(8):1304–1305

Checked 9 Nov 2026. Kothari RU, Brott T, Broderick JP, et al., “The ABCs of measuring intracerebral hemorrhage volumes”, Stroke 1996;27(8):1304–1305 (formula ABC/2; A greatest diameter, B diameter at 90° to A, C = number of slices × slice thickness; abstract). Slice weighting described as in the full paper (standard practice).

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