Visceral fat rating vs visceral fat area: what each number means

Visceral fat is the fat inside the abdomen, around the organs. Fat under the skin is subcutaneous fat. Three common numbers try to describe the visceral part, and each one comes from a different method. Before you compare a result with a chart or with an older reading, find out which of these three numbers you have.

Three visceral fat numbers. The reference lines belong to their own methods and do not convert into each other.

A rating of 12 and an area of 120 cm² are not two ways to write the same thing. The first number is a position on one maker's scale. The second is an area in square centimetres. If a number has no unit beside it, treat it as a device score until the device's manual says otherwise.

So the same score can sit in different places on different devices. A hypothetical reading of 11 is inside Tanita's 1 to 12 band. On InBody's level scale, 11 is above the recommended line of 10. Each maker defines its own score, so do not move a reading from one brand onto another brand's chart.

InBody's page gives two separate lines, a level under 10 or an area under 100 cm². It does not give a formula that links them. Tanita's page does not publish a conversion either. Do not multiply a Tanita rating by 10, or by any other factor, to get square centimetres. If the manual for your device gives no conversion, keep the rating as a score.

These lines come from particular groups of people, scan levels and outcomes. A 100 cm² line from Japanese adults scanned at the navel is not automatically the right line for a different population, a different scan level or a scale reading. Body Numeral's visceral fat calculator shows 130 cm² as a comparison line. The tape equations below were tested against CT areas above 130 cm² at L4–L5, with the 1994 study as the source for that line. That study included men only, so the line is weaker evidence for women. Use it as a reference for reading an estimate, not as a personal target.

These studies tested particular devices in particular groups, so they do not rate every scale. They do show two practical points. One abdominal impedance device's visceral fat level followed total belly fat more closely than the fat around the organs. And in the scale study, a rating inside the maker's healthy band did not show that the CT result was also low. The guide on smart scale accuracy explains how impedance estimates work and why they can change with conditions such as hydration.

The equation for men is 6 × waist − 4.41 × proximal thigh + 1.19 × age − 213.65, with the measurements in centimetres and age in years. Take a hypothetical man aged 45 with a 94 cm waist and a 56 cm proximal thigh. These numbers are invented to show the arithmetic.

1. Waist term: 6 × 94 = 564.
2. Thigh term: 4.41 × 56 = 246.96.
3. Age term: 1.19 × 45 = 53.55.
4. Combine the terms: 564 − 246.96 + 53.55 − 213.65 = 156.94.
5. Round for display: about 157 cm² estimated visceral fat area.

The equation for women is 2.15 × waist − 3.63 × proximal thigh + 1.46 × age + 6.22 × BMI − 92.713. BMI is weight in kilograms divided by height in metres squared. The visceral fat calculator does this arithmetic and shows the equation it used. It rejects a result below zero, because a negative area means the equation does not fit those measurements.

The 157 cm² in the example is an equation estimate. It has the same unit as a CT area, but no image was measured. Because the waist term has a large multiplier in the men's equation, a 1 cm change in the waist reading moves the estimate by 6 cm². The thigh term is almost as sensitive: 1 cm of thigh moves the estimate by 4.41 cm². Take each measurement at the stated site every time. The waist is midway between the lowest rib and the top of the hip bone, after a normal breath out. The proximal thigh is measured just below the fold under the buttock. The tape measurement guide explains how to keep the tape level and snug.

• Write the method beside every number: the device model and "rating", or "cm² from tape equation", or "cm² from CT".
• Compare scale ratings only with ratings from the same scale, under similar conditions such as time of day, food, drink and exercise.
• Compare tape estimates only with tape estimates that use the same equation and measurement sites.
• Keep the reference line with the method that produced it. Do not read a scale rating against an imaging cut-off, or a tape estimate against a scale maker's bands.

A change of one or two rating points can come from the measurement itself. So can 10 cm² or more in a men's tape estimate, because a 1 cm difference in the waist reading alone moves it by 6 cm². Look at several readings over weeks before you read a direction into the numbers. If the method changes, start a new series instead of joining the two. The guide on comparing repeated measurements explains how to keep method changes visible.

A clinician who needs a direct measure uses an imaging method suited to the question. If a home reading worries you, take the numbers and the method names to that conversation, rather than a converted value.