How do I calculate my BMI?

Divide your weight in kilograms by your height in metres squared. For example, 80 kg ÷ (1.75 m × 1.75 m) = 26.1. The calculator above does this for you and accepts stone and feet.

BMI is a quick screening measure, not a diagnosis. It does not tell muscle from fat, so very muscular people can have a high BMI without carrying excess fat. Measuring your waist alongside BMI gives a better picture.

What waist size is healthy?

The NHS suggests keeping your waist to less than half your height. At 170 cm tall, that means a waist under 85 cm (about 33.5 inches).

BMI calculator

Work out your body mass index (BMI) using stone and feet or kg and cm, and see the healthy weight range for your height.

By the Calori team · Updated 21 October 2026 · 3 min read

Height

Weight

Ethnic background

Your BMI

24.5

Healthy weight

Healthy range

57–76kg

8 st 13 lb to 12 st 0 lb

Status

In range

for your height

What is BMI?

Body mass index compares your weight with your height. It is the measure the NHS and GPs use to check whether an adult's weight is in a healthy range. The formula is your weight in kilograms divided by your height in metres squared.

BMI ranges for adults

The NHS uses lower cut-offs for people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background, because health risks such as type 2 diabetes start at a lower BMI.

BMI (most adults)	Category	BMI (lower cut-offs)
Below 18.5	Underweight	Below 18.5
18.5 to 24.9	Healthy weight	18.5 to 22.9
25 to 29.9	Overweight	23 to 27.4
30 to 39.9	Obese	27.5 to 39.9
40 or above	Severely obese	40 or above

This calculator is for adults aged 18 and over. Children's BMI is judged against age and sex charts instead.

What BMI does not tell you

Muscle and fat weigh the same on the scale. A rugby player can have a BMI over 30 with little body fat.
Where you carry fat matters. Fat around the waist carries more health risk than fat elsewhere. Keep your waist to less than half your height.
It does not change with age. Older adults often lose muscle, so the same BMI can mean more body fat.

If your BMI is above the healthy range

Losing even 5% of your body weight improves blood pressure, blood sugar and cholesterol. For most people the most reliable approach is a moderate calorie deficit with plenty of protein. Work out your numbers with our calorie calculator, and read how to lose a stone for a step-by-step plan.

Need to convert your weight first? Use the stone to pounds and kg converter.

Talk to your GP if your BMI is below 18.5 or 30 or above, or if you are worried about your weight. This calculator is for general information and is not medical advice.

Frequently asked questions

What is a healthy BMI?: For most adults a BMI of 18.5 to 24.9 is in the healthy weight range. For people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background, the NHS uses 18.5 to 22.9.
How do I calculate my BMI?: Divide your weight in kilograms by your height in metres squared. For example, 80 kg ÷ (1.75 m × 1.75 m) = 26.1. The calculator above does this for you and accepts stone and feet.
Is BMI accurate?: BMI is a quick screening measure, not a diagnosis. It does not tell muscle from fat, so very muscular people can have a high BMI without carrying excess fat. Measuring your waist alongside BMI gives a better picture.
What waist size is healthy?: The NHS suggests keeping your waist to less than half your height. At 170 cm tall, that means a waist under 85 cm (about 33.5 inches).