BMI Calculator

BMI Formula & Categories

Body Mass Index (BMI) = weight (kg) ÷ height (m)². This calculator accepts stones and pounds with feet and inches, or kilogrammes and centimetres.

BMI Categories for Adults (NHS / WHO)

BMI does not distinguish muscle from fat and is not suitable for athletes or pregnant women. Results are for reference only — speak to your GP about any health concerns.

Frequently Asked Questions

What is a healthy BMI?

Using the standard NHS/WHO ranges, a BMI of 18.5–24.9 is a healthy weight, below 18.5 is underweight, 25–29.9 is overweight, and 30 or above is obese.

How is BMI calculated?

BMI = weight (kg) ÷ height (m)². For example, 72 kg at 1.75 m gives a BMI of about 23.5. The calculator converts stones, pounds, feet and inches for you.

Is BMI accurate?

BMI does not distinguish muscle from fat, so it can be misleading for athletes, pregnant women and older adults. Use it as a general screening tool and consider your waist measurement and body-fat percentage too.

What is my healthy weight range?

A healthy weight is a BMI of 18.5–24.9 multiplied by your height (m)². At 1.75 m that is roughly 57–76 kg, or about 8 st 13 lb to 11 st 13 lb.

Does the NHS use a different BMI range?

The NHS uses the same WHO adult ranges, but advises that people of Black, Asian and some other ethnic backgrounds may face higher health risks from a BMI of 23 or above. Treat the cut-offs as guidance, not strict limits.