Body Indexes Calculator

Enter weight, height and waist size

Enter weight, height, and waist size in any units; each column stays in sync. BMI uses weight and height; BRI uses waist size and height.

Weight

Kilograms

Pounds (lb)

Stones

Whole stones and pounds (LB) —

Height

Centimetres (cm)

Metres (m)

Feet (ft)

Inches (in)

Whole feet and inches —

Waist Size (BRI only)

Centimetres (cm)

Inches (in)

Body Mass Index (BMI) - Traditional —

Body Mass Index (BMI) - Alternative —

Body Roundness Index (BRI) —

Traditional BMI = kg ÷ m². Alternative BMI = 1.3 × kg ÷ m^2.5 (Nick Trefethen, University of Oxford). BRI = 364.2 − 365.5 × √(1 − (waist ÷ 2π)² ÷ (height ÷ 2)²) with waist and height in metres.

Note: We do not check the numerical validity of your inputs to ensure sensible values for a human so have fun :). Nothing here constitutes health advice of any kind.

How this BMI and BRI calculator works

What it measures

Body Mass Index relates weight to height. Body Roundness Index adds waist circumference to approximate abdominal roundness. Both are adult screening indexes — not direct body-fat percentages and not diagnoses.

Formulas

Traditional BMI = kg ÷ m². Alternative BMI = 1.3 × kg ÷ m^2.5 (Trefethen). BRI uses waist and height in metres: 364.2 − 365.5 × √(1 − (waist ÷ 2π)² ÷ (height ÷ 2)²).

Worked example

80 kg at 175 cm → BMI ≈ 26.1. A 90 cm waist raises BRI compared with a slimmer waist at the same weight, flagging central fat the scale alone may miss.

Common mistakes

Mixing pounds with metres without converting.
Measuring waist over bulky clothing.
Treating BMI as a body-fat percentage.

FAQs

Which BMI?: WHO charts use traditional BMI; the alternative tweaks tall/short extremes slightly.
Guides?: Understanding BMI and BRI · BMI vs BRI vs body fat.

When this page helps

Use it when you want a transparent, browser-side calculation with the assumptions spelled out — then verify anything high-stakes against primary docs, a professional, or your own measurements. The related links below point to sibling tools and longer guides when you need more context.

Accuracy notes

Results depend entirely on the numbers you enter and the simplified model described above. Device clocks, tape measurements, market rates, and recipe conventions can all differ from a perfect textbook case. If an output looks surprising, re-check units first, then re-read the formula section.

Last updated: July 2026