About the Body Roundness Index Calculator
The body roundness index, or BRI, estimates body shape from your waist and your height. It treats the body as an ellipse and gives a higher number for a rounder shape. Researchers have linked a higher BRI to more body fat around the middle. This calculator takes the waist and the height in centimetres. Type waist and height in centimetres and the body roundness index appears at once, with a few related figures underneath, and you can copy the result with one tap. The sums run in your browser, so nothing you enter is uploaded.
Updated October 2026
How to use the Body Roundness Index Calculator
- 1Enter waist and height in centimetres.
- 2Pick the units or options from the menus if the body roundness index tool offers them.
- 3Read the body roundness index in the large result box.
- 4Look at the extra rows for related figures.
- 5Press Copy result to keep the answer.
When you need the body roundness index
People use it as another health check next to BMI and waist-to-height ratio.
Values of 1 to 3 are low, 3 to 5 is mid-range, and above 5 or so suggests more fat around the waist. A BRI cannot replace a medical opinion.
How the body roundness index is worked out
BRI = 364.2 − 365.5 × √(1 − ((waist ÷ 2π)² ÷ (0.5 × height)²)). A waist of 85 cm and a height of 175 cm give a BRI of about 3.1. A waist of 100 cm at the same height gives about 4.8.
Every answer on this page comes from that one rule, so you can check any result by hand with a calculator. The figures shown underneath, such as other units, are conversions of the same answer.
- Waist and height only
- No weight needed
- Eccentricity shown
Mistakes to avoid with body roundness index
Measure the waist at the navel, relaxed, with a tape. Do not use this for children, and speak to a doctor about health concerns.
On phone and computer
On a phone, type into the boxes one after another and read the body roundness index underneath; Copy result puts it on the clipboard for a message or a note. On a computer the inputs sit on the left and the answer on the right, so you can change one figure and watch the body roundness index move. The body roundness index calculator works the same on both.
Checking your body roundness index by hand
A good habit is to test the body roundness index calculator with a case you already know. A waist of 85 cm and a height of 175 cm give a BRI of about 3.1. A waist of 100 cm at the same height gives about 4.8.
If your own figures give a surprising answer, repeat the working yourself: BRI = 364.2 − 365.5 × √(1 − ((waist ÷ 2π)² ÷ (0.5 × height)²)). Small differences usually come from rounding, from mixing units, or from a typing slip in one of the inputs. A waist-based figure is more useful when you look at it alongside others. Use the Waist to Height Ratio Calculator for a simple rule of thumb, the Waist-to-Hip Ratio Calculator for body shape, and the BMI Calculator for the number most people already know.
Features
- Measure at the navel
- Adults only
- A screening number
- Clear messages when the body roundness index inputs make no sense
- Copy the result with one tap
- Private: nothing is uploaded
Frequently asked questions
How do I calculate body roundness index?
BRI = 364.2 − 365.5 × √(1 − ((waist ÷ 2π)² ÷ (0.5 × height)²)). A waist of 85 cm and a height of 175 cm give a BRI of about 3.1. A waist of 100 cm at the same height gives about 4.8.
What is the formula for body roundness index?
BRI = 364.2 − 365.5 × √(1 − ((waist ÷ 2π)² ÷ (0.5 × height)²)). The body roundness index calculator applies it exactly and rounds only the displayed answer to six significant figures.
What is a healthy BRI?
Researchers often find the lowest risk between about 3 and 4, but there is no strict cutoff.
How does it differ from BMI?
It uses waist and height rather than weight.
Is it a diagnosis?
No. It is a screening number.
Is this body roundness index calculator free and private?
Yes. It is free, needs no account and runs in your browser, so the numbers you type are not uploaded or stored.