Free online tool for adults aged 18 and over
This BMI calculator UK page takes your weight in stones and pounds or kg and your height in feet and inches or cm. It shows your BMI category, then estimates your BMR and daily calorie needs. Children and pregnant women need different charts, so ask a clinician.
BMI chart UK: what your BMI means
This BMI chart is for adults aged 18 and over. NHS BMI categories, which follow World Health Organization (WHO) classifications, define your BMI number as follows (kg/m2). The same ranges apply to the BMI chart for women, the BMI chart for men, and the BMI chart in stones.
| BMI Range | NHS Category | What It Means |
|---|---|---|
| Below 18.5 | Underweight | May indicate nutritional deficiency or underlying conditions. Discuss with your GP. |
| 18.5 to 24.9 | Healthy weight | Associated with the lowest population-level risk of cardiometabolic conditions. |
| 25.0 to 29.9 | Overweight | May increase long-term risk of type 2 diabetes and hypertension without lifestyle management. |
| 30.0 to 34.9 | Obese (Class I) | Standard NHS threshold for structured weight management and private GLP-1 eligibility. |
| 35.0 to 39.9 | Obese (Class II) | Meets NICE criteria for tier 3 specialised weight management and medical treatments. |
| 40.0 and above | Obese (Class III / Severe) | Highest metabolic risk category; qualifies for specialist clinical interventions and bariatric pathways. |
Lower thresholds for ethnic minority backgrounds
NICE guidelines explicitly state that health risks associated with excess weight occur at lower BMI levels in adults of South Asian, Chinese, Black African, and African-Caribbean family backgrounds. For these groups, overweight starts at BMI 23.0 and obesity starts at BMI 27.5.
Waist circumference: The vital companion metric
BMI cannot measure where fat is stored. Visceral fat wrapped around internal organs poses greater health risks than subcutaneous fat under the skin. NHS guidance recommends measuring waist circumference:
- • Women: Increased health risk at 80 cm (31.5 inches) or above; very high risk at 88 cm (34.5 inches).
- • Men: Increased health risk at 94 cm (37 inches) or above; very high risk at 102 cm (40 inches).
Weight management eligibility — what BMI can (and cannot) tell you
BMI categories help clinicians triage who may benefit from structured weight management support. In the UK, prescription weight loss medicines, whether private or on the NHS, typically require:
- • BMI of 30 kg/m² or above without other conditions.
- • BMI of 27 kg/m² or above with at least one weight-related medical condition (e.g. hypertension, dyslipidaemia, obstructive sleep apnoea, or pre-diabetes).
- • Reduced by 2.5 kg/m² for individuals from South Asian, Chinese, Black African, or African-Caribbean backgrounds.
Each medicine has its own rules, and a prescriber makes the final decision. Read our BMI eligibility guide.
BMI calculator for women and men
The BMI calculator for women and the BMI calculator for men use the same formula and the same adult categories, so a BMI of 27 means the same thing on the chart for either. What differs is body composition. At the same BMI, women usually carry more body fat than men, and men usually carry more muscle mass.
That is why waist circumference helps. The waist limits above are lower for women (80 cm) than for men (94 cm). Pick your sex in the BMR tab of the calculator for a calorie estimate, as the formula uses it.
How to calculate BMI
A body mass index calculator works out BMI from your height and weight using weight ÷ height² (weight in kilograms, height in metres). A BMI calculator estimates your number so you can place it in context. It is not a diagnosis.
For example, if you weigh 70 kg and are 1.75 m tall, your height squared is 3.06. Divide 70 by 3.06 and your BMI is about 22.9, which is in the healthy weight range.
Enter your weight in stones and pounds or kg. This BMI calculator takes stones as well as metric units, and height can be entered in feet and inches or cm. To work it out by hand from stones, convert to kg first: one stone is about 6.35 kg.
Healthy weight range for your height
To work out your ideal weight range, use the healthy BMI range of 18.5 to 24.9 for your height. At 1.75 m, that is about 57 kg to 76 kg (9 st to 12 st). It is a range, not a single target, and muscle mass can move it.
BMR and TDEE calculator: your daily calorie needs
Our BMR calculator uses the Mifflin–St Jeor equation (weight, height, age, and sex) to estimate calories burned at rest. Multiplying BMR by an activity factor gives an estimated TDEE—your approximate daily calorie needs for maintenance—then mild or moderate deficit ranges for planning.
Treat these figures as planning guides. Real needs vary with muscle mass, hormones, medications, and how accurately you pick an activity level. Agree low-calorie plans with a GP or dietitian if you have medical conditions.
BMR is the energy your body uses at rest. The TDEE adds movement and exercise on top, so it is the figure to start from when you plan a calorie deficit. A modest deficit below your TDEE is gentler than eating down to your BMR.
Want to follow your progress over time? Use our weight loss tracker.
FAQs
Is BMI accurate?
- BMI is a good guide, but it is not exact. It uses only your height and weight. It does not measure body fat or muscle mass. A very muscular person can have a high BMI. An older adult can have a healthy BMI and still carry too much body fat. That is why we also look at waist size and ethnic background. Think of BMI as a first check, not a diagnosis.
What is BMR basal metabolic rate?
- BMR means basal metabolic rate. It is the number of calories your body burns at rest in a day. It is the energy you need just to stay alive.
Ideal weight calculator UK: what is my ideal weight?
- There is no one perfect number. The best way is to use an ideal weight calculator UK style and look at a range. Enter your height above, and we show the healthy weight range for you. Anywhere in that range is a good place to be.
What is good BMI for your age and weight?
- For adults, the healthy BMI range is 18.5 to 24.9 at any age. What is good for you depends on your height, not just your age and weight. Ask your GP if you are 65 or over.
What is the difference between BMR and TDEE?
- BMR is what you burn at rest. TDEE is what you burn over the whole day, including movement and exercise. TDEE is always higher than BMR.
What is a BMI calculator?
- A BMI calculator is a tool that does the BMI sum for you. You enter your height and weight. It shows your body mass index and your weight group.
Can children use this tool?
- No. It is for adults aged 18 and over. Ask your GP or school nurse about a child's weight.
