Calculate fibroid volume from three ultrasound or MRI diameter measurements (D1 × D2 × D3) using the standard ellipsoid volume formula used in radiology.
Fibroid volume is estimated from three perpendicular diameter measurements taken on ultrasound or MRI — the length, width and height of the fibroid — multiplied together and then by a constant of 0.5233. This is the standard ellipsoid volume formula used in radiology because most fibroids approximate an oval (ellipsoid) shape. The result is given in cubic centimetres (cm³), which is numerically equivalent to millilitres (mL).
⚕️ Medical Notice: This calculator uses the same ellipsoid formula radiologists and sonographers use to estimate fibroid volume from a scan. However, your official radiology or gynaecology report is always the authoritative measurement. This tool is intended to help you understand and track numbers from a scan report — it does not replace your doctor's interpretation of size, number, location, or clinical significance. Consult your GP or gynaecologist for medical advice.
Scan report in mm? Divide by 10 to convert to cm before entering (e.g. 42 mm = 4.2 cm).
| Parameter | Value |
|---|
On an ultrasound or MRI scan, a sonographer or radiologist typically measures a fibroid in three dimensions. The longest diameter is usually measured first, in one imaging plane (commonly the axial plane) — this becomes D1. The second measurement, D2, is the largest diameter that runs perpendicular to D1 within that same plane. The third measurement, D3, is then taken in a perpendicular plane, such as the sagittal or coronal view, capturing the fibroid's depth or height. Together these three perpendicular measurements approximate the fibroid's overall three-dimensional size, in the same way length, width and height describe a solid object.
The constant 0.5233 comes from the formula for the volume of an ellipsoid (approximately 4/3 × π × r1 × r2 × r3, simplified using diameters instead of radii). It is a well-established approximation used widely in radiology because it is quick to calculate from routine measurements and is generally reliable for typical, roughly oval-shaped fibroids.
Fibroid volume numbers on a scan report can be hard to picture. Doctors sometimes use everyday fruit comparisons purely as a communication aid, to help you visualise roughly how large a fibroid is. These comparisons are approximate and are not a measure of medical significance — a "grapefruit-sized" fibroid is not automatically more concerning than a smaller one, since location and symptoms matter far more than size alone.
| Approximate Volume | Everyday Size Comparison |
|---|---|
| Under 1 cm³ | Pea-sized |
| ~1–8 cm³ | Grape-sized |
| ~8–30 cm³ | Walnut-sized |
| ~30–65 cm³ | Lime-sized |
| ~65–150 cm³ | Lemon-sized |
| ~150–300 cm³ | Orange-sized |
| ~300–650 cm³ | Grapefruit-sized |
| Over 650 cm³ | Melon-sized |
Unlike measurements such as blood pressure, there is no universal "normal versus abnormal" volume threshold for fibroids. A fibroid's clinical significance depends on several factors together, not volume in isolation: its location within the uterus (submucosal, intramural, or subserosal), the number of fibroids present, and whether it is causing symptoms such as heavy bleeding, pain, or pressure. A small submucosal fibroid can sometimes cause more disruptive symptoms than a much larger subserosal one, simply because of where it sits. This is why your doctor looks at the full picture from your scan report rather than volume alone.
| Type | Location | General Notes |
|---|---|---|
| Submucosal | Just under the inner lining of the uterus (endometrium) | Most likely to affect periods and fertility even when small |
| Intramural | Within the muscular wall of the uterus | Most common type; can enlarge the uterus if numerous or large |
| Subserosal | On the outer surface of the uterus | Can press on nearby organs (e.g. bladder, bowel) as they grow |
What is the ellipsoid formula and why is it used for fibroids?
The ellipsoid formula (Volume = D1 × D2 × D3 × 0.5233) estimates the volume of a rounded, oval-shaped object from three perpendicular diameters. It is used for fibroids because most fibroids are roughly oval in shape, and the formula is quick to apply using standard measurements a sonographer or radiologist already takes during a routine scan.
How accurate is the ellipsoid formula for fibroid volume?
It is generally reliable for fibroids that are fairly regular and oval-shaped. However, it is still an approximation. For irregularly-shaped fibroids, studies comparing this formula to more precise 3D volumetric imaging have found differences exceeding 20% in a meaningful minority of cases. Your official scan report's stated volume should always be treated as more authoritative than a manual recalculation.
What do D1, D2 and D3 mean on my scan report?
D1, D2 and D3 refer to the three perpendicular diameters of the fibroid. D1 is typically the longest diameter measured in one imaging plane (often axial), D2 is the largest diameter perpendicular to D1 in that same plane, and D3 is measured in a different, perpendicular plane (such as sagittal or coronal) to capture depth. Together they describe the fibroid's size in three dimensions.
Does fibroid volume alone tell me if I need treatment?
No. Volume is only one piece of information. Whether treatment is needed depends much more on the fibroid's location (submucosal, intramural or subserosal), the number of fibroids present, and your symptoms — such as heavy or prolonged periods, pain, pressure, or effects on fertility. Two fibroids of the same volume can have very different clinical significance depending on where they sit.
Can fibroid volume change over time?
Yes. Fibroids can grow or shrink over time, often influenced by hormonal changes. They frequently grow during the reproductive years, can enlarge during pregnancy, and commonly shrink after menopause as oestrogen levels fall. Your doctor may recommend periodic scans to track any change in size.
What are the main types of fibroids by location?
Fibroids are generally classified by where they sit in the uterus: submucosal (just under the inner lining, most likely to affect periods and fertility), intramural (within the muscular wall, the most common type), and subserosal (on the outer surface, which can press on nearby organs as they grow). Some fibroids span more than one zone.
Why might my calculated volume differ slightly from my radiology report?
Small differences can come from rounding of the diameter measurements, slight variation in exactly where each diameter was measured, or the fact that some modern imaging uses more detailed 3D volumetric techniques rather than the simplified ellipsoid formula. These differences are usually minor and expected — the figure on your official report is the one your doctor will rely on.
How often are fibroids monitored with follow-up scans?
This varies widely depending on the fibroid's size, location, your symptoms, and your individual circumstances (such as whether you are trying to conceive or approaching menopause). Some fibroids are monitored annually, others less often, and some not at all if they are small and not causing problems. Ask your doctor what monitoring schedule is right for you.
Can this calculator diagnose or assess my fibroid for me?
No. This calculator only performs the arithmetic of the standard ellipsoid volume formula from measurements you enter. It cannot assess shape irregularity, location, symptom impact, or clinical significance. Only a radiologist, sonographer, or your treating doctor can properly interpret a fibroid scan.