--- title: "BMI Calculator UK: Stones, Pounds and NICE Bands | AumnI tools" description: "Work out BMI from centimetres and stones or pounds, see the NICE and NHS category and the healthy weight range, with a lower-threshold option for some backgrounds." url: https://aumnitools.com/uk/tool/bmi-calculator category: "Health" country: "United Kingdom" updated: 2026-11-08 --- # BMI Calculator In the UK, body weight is usually quoted in stones and pounds, and BMI is read against the NICE and NHS adult bands. This page opens on centimetres and stones, names the category from Underweight to Obesity class 3, and offers a checkbox for the lower NICE thresholds that apply to some ethnic backgrounds. It is a screening measure, so take the number to a GP to interpret. ## United Kingdom rules and figures - The UK page follows NICE and NHS adult categories, where Healthy weight is 18.5 to 24.9 and Obesity splits into class 1, class 2 and class 3 at 30, 35 and 40. - NICE says people with a South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background are at risk at a lower BMI: overweight from 23 to 27.4 and obesity from 27.5. - The NHS has a separate BMI calculator for children and teenagers aged 2 to 17, and the adult bands on this page do not apply to them. - Stones and pounds are the default weight unit and centimetres the default height unit on the UK page, so 11 st 0 lb is entered as two numbers rather than as 154 lb. Sources: [NICE NG246: Classifying overweight and obesity in adults](https://www.nice.org.uk/guidance/ng246/chapter/identifying-and-assessing-overweight-obesity-and-central-adiposity) (checked 2026-11-08); [NHS: Obesity diagnosis](https://www.nhs.uk/conditions/obesity/diagnosis/) (checked 2026-11-08); [NHS: BMI calculator](https://www.nhs.uk/health-assessment-tools/calculate-your-body-mass-index/) (checked 2026-11-08) ## How the BMI calculator works Stones and pounds are changed to kilograms (14 lb to the stone, 0.45359237 kg to the pound), divided by height in metres squared, then placed in the NICE and NHS band that contains the result. Formula: `BMI = kg ÷ m². NICE and NHS bands: Underweight < 18.5, Healthy weight < 25, Overweight < 30, Obesity class 1 < 35, class 2 < 40, class 3 above. Lower-threshold option: overweight from 23, obesity from 27.5` - Height starts in centimetres and weight in stones and pounds, with 170 cm and 11 st 0 lb already filled in. If you choose kg, lb or ft instead, that choice is kept. - The Healthy Weight Range runs from 18.5 × height² to 24.9 × height² and is printed in stones and pounds. With the lower thresholds ticked it ends at 22.9 × height² instead. - Only the UK page shows the checkbox, because NICE gives numbers for the lower thresholds: overweight from 23 to 27.4 and obesity from 27.5, for South Asian, Chinese, other Asian, Middle Eastern, Black African and African-Caribbean backgrounds. - The adult bands do not apply to children. The NHS has its own BMI calculator for ages 2 to 17, and this page says so under the result. ## How to use the BMI calculator 1. **Enter height and weight.** Type height in centimetres, then stones and pounds in the two weight boxes. Use the small unit boxes to switch to feet and inches or to kilograms. 2. **Tick the lower thresholds if they fit.** The box under the method list moves the overweight and obesity cut-offs down to 23 and 27.5 for the backgrounds NICE names. 3. **Read the category and range.** The big number is your BMI with its NICE band underneath. Beneath that, Healthy Weight Range gives the stone and pound limits of the healthy band at your height. 4. **Add waist and neck sizes.** The Body Composition tab turns waist, hip and neck measurements in centimetres into ratios. 5. **Copy or keep the result.** Copy sends the figures to the clipboard and Save Entry adds a dated row for tracking in this browser. ## Example: 170 cm and 11 st 0 lb, with and without the lower thresholds With 170 cm and 11 st 0 lb, the page shows 24.2 and Healthy weight, with 8 st 5.9 lb to 11 st 4.6 lb as the range. Tick the lower-threshold box and 24.2 stays put, but the label turns to Overweight and the range stops at 10 st 5.9 lb. For 175 cm and 14 st 7 lb the result is 30.1, Obesity class 1. ## When to use the BMI calculator - **Reading a weight given in stones.** Enter 12 st 3 lb as two numbers and get the BMI and category without converting to kilograms first. - **Checking the lower thresholds.** Tick the box to see how the category and healthy range change when overweight starts at 23. - **Preparing for a GP appointment.** Note the BMI, the category and your waist measurement so the conversation starts with the same figures. ## What the BMI calculator does not do - BMI uses height and weight only. It cannot separate muscle from fat or show where weight is carried. - The checkbox applies the NICE lower thresholds to the whole result. It does not ask which background you have, so only use it if one of the listed backgrounds fits. - Choosing Age-Adjusted BMI at 65 or over swaps NICE for 23, 28 and 33, figures this page chose itself. - This is a screening figure, not a diagnosis. A GP can judge it alongside waist size, blood tests and family history. ## When something else is a better fit - **When you want to see body fat from a tape measure rather than BMI**, use the [Body Fat Calculator](https://aumnitools.com/tool/body-fat-calculator.md). - **When you are choosing target weights by formula for your height**, use the [Ideal Weight Calculator](https://aumnitools.com/tool/ideal-weight-calculator.md). - **When you want your result interpreted for your own health**, use a GP or practice nurse, who can combine BMI with waist size and other checks. ## Questions about the BMI calculator ### Which BMI categories does the UK page use? The NICE and NHS adult bands, where 18.5 to 24.9 is Healthy weight and Obesity has classes 1, 2 and 3 starting at 30, 35 and 40. The tool names the source under the result. ### When should I tick the lower-threshold box? Tick it if your background is South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean, the groups NICE names. Overweight then starts at 23 and obesity at 27.5. A GP can confirm which applies to you. ### Why is my weight range printed in stones? The page starts in stones and pounds because that is how weight is usually stated in the UK. At 170 cm the healthy range reads 8 st 5.9 lb to 11 st 4.6 lb, and switching the unit to kg gives 53.5 to 72 kg. ### Can I use this for my child? No. The adult bands do not apply under 18, and the NHS points to its own BMI calculator for children and teenagers aged 2 to 17, which compares them with others of their age. ### Is a BMI of 24.2 always healthy? It is inside the Healthy weight band on the standard UK cut-offs. With the lower thresholds ticked, 24.2 falls in Overweight. Either way it is a screening figure, and a GP can say what it means for you. ## Related tools - [Body Fat Calculator](https://aumnitools.com/tool/body-fat-calculator.md): Estimates body fat from neck, waist and height tape measurements with the US Navy formula - [Ideal Weight Calculator](https://aumnitools.com/tool/ideal-weight-calculator.md): Runs six ideal weight formulas for your height and shows the BMI 18.5 to 24.9 weight band - [Calorie Calculator](https://aumnitools.com/tool/calorie-calculator.md): Estimates BMR and daily calorie needs, with gram targets for protein, carbs and fat ## About this page Runs in your browser: what you enter is processed on this device and is not uploaded. Age, gender, goals and saved entries are kept in this browser's local storage and are never uploaded. General information only, not medical advice. Talk to a doctor or other health professional about decisions that affect your health. Last checked against the tool's code on 2026-11-08. Interactive version: https://aumnitools.com/uk/tool/bmi-calculator