BMI Calculator
Check your result against clinical guidelines, understand what your score means for your health, and discover whether you could be eligible for weight loss treatment.
BMI calculator
Body mass index (BMI) is one of the most widely used tools in healthcare. Enter your height and weight into our BMI calculator, and you'll get an instant snapshot of where your weight sits relative to clinical guidelines.
But a number on its own only tells part of your health story. Read on to understand what your result means, where it helps to calculate other measurements alongside BMI, and what you can do next.
Your BMI result
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| Underweight | Healthy | Overweight | Obesity |
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What is BMI and how is it calculated?
BMI stands for body mass index. It's a simple formula that uses your height and weight to give a numerical value that broadly indicates whether you're carrying too little, too much, or an appropriate amount of weight for your size.
Despite its age, BMI remains the standard screening measure used by the WHO, NICE, and health organisations worldwide because it's quick, non-invasive, and costs nothing to calculate.
Our calculator supports both metric measurements (kg and cm) and imperial measurements (stones, pounds, feet, and inches), so you can use whichever you're most comfortable with.
BMI is calculated using a simple formula:
weight (kg) ÷ height² (m²)
What does that mean in practice?
If you weigh 80 kg and are 1.75 m tall, the calculation looks like this:
80 ÷ (1.75 × 1.75) = 26.1
A BMI of 26.1 falls into the overweight range, just above the healthy weight threshold of 24.9.
Understanding your results: what is a healthy BMI?
The WHO uses the same adult BMI categories:
| BMI | Category |
|---|---|
| 18.4 and below | Underweight |
| 18.5–24.9 | Healthy weight |
| 25.0–29.9 | Overweight |
| 30.0–34.9 | Obese (Class 1) |
| 35.0–39.9 | Obese (Class 2) |
| 40.0 and above | Obese (Class 3) |
These are population-level guidelines, not a diagnosis. A BMI in the overweight range isn't automatically cause for alarm, and a BMI in the healthy range doesn't guarantee good health.
Start your clinical assessmentDoes ethnicity affect your BMI?
Standard BMI thresholds were developed primarily using data from white European populations. Research now shows clearly that people from other ethnic backgrounds can develop obesity-related health complications at lower BMI values.
NICE now recommends lower BMI thresholds for people from South Asian, Chinese, other Asian, Middle Eastern, Black African, and African-Caribbean backgrounds.
| Category | Standard | Adjusted |
|---|---|---|
| Overweight | 25.0 kg/m² | 23.0 kg/m² |
| Obese | 30.0 kg/m² | 27.5 kg/m² |
If your BMI is above 23.0 kg/m² and you're from one of these ethnic groups, it's worth speaking to a clinician about your individual risk.
Is BMI always accurate?
BMI is a useful screening tool, but it does have some limitations when applied to individuals.
Beyond BMI: why waist-to-height ratio matters
NICE recommends measuring waist-to-height ratio (WHtR) alongside BMI in adults with a BMI below 35 kg/m², as a practical way to assess fat stored around the abdomen (central adiposity).
As a working guide, a waist circumference of less than half your height (0.5 or under) falls within the healthy range. NICE uses the following thresholds:
- • WHtR below 0.5: healthy central adiposity
- • WHtR 0.5–0.59: increased health risk
- • WHtR 0.6 or above: high health risk
Measuring your WHtR is simple
Find Midpoint
Use a tape measure to find the midpoint between your lowest rib and the top of your hip bone.
Record Waist
Record that measurement comfortably. This usually falls around your belly button.
Calculate Ratio
Divide your waist circumference by your height (both in cm or inches) to find your ratio.
BMI and GLP-1 weight management medication
GLP-1 receptor agonists are among the most effective medications currently available for weight management. Eligibility is based on specific BMI criteria set by clinical guidelines.
Standard criteria
- • BMI ≥ 30 kg/m²
- • Or BMI 27–30 with a weight-related condition
- • Age 18 or over
South Asian adjusted criteria
- • BMI ≥ 27.5 kg/m²
- • Or BMI 25–27.5 with a weight-related condition
- • Lower threshold due to higher metabolic risk
This information is intended for educational purposes only. Prescription treatment is subject to clinical assessment and may not be suitable for everyone.
Learn more about treatment optionsWhat counts as a weight-related health condition?
For the purposes of clinical guidance, qualifying conditions include type 2 diabetes, hypertension (high blood pressure), obstructive sleep apnoea, and cardiovascular disease, among others.
GLP-1 medications are designed to be used as part of a clinically managed weight management programme, and not as standalone solutions.
Learn more about treatment options →Common qualifying conditions
- • Type 2 diabetes
- • High blood pressure
- • Obstructive sleep apnoea
- • Cardiovascular disease
- • Dyslipidaemia
Calculating BMI: your questions answered
References
1. Wu Y, Li D, Vermund SH. Advantages and limitations of the body mass index (BMI) to assess adult obesity. Int J Environ Res Public Health. 2024.
2. Caleyachetty R, et al. Ethnicity-specific BMI cutoffs for obesity based on type 2 diabetes risk in England. Lancet Diabetes Endocrinol. 2021.
3. National Institute for Health and Care Excellence. Semaglutide for managing overweight and obesity [TA875]. London: NICE; 2023.
4. Ashwell M, et al. Waist-to-height ratio as an indicator of early health risk. PLoS ONE. 2016.
Ready to take control of your health?
Book a free consultation with our clinical team to discuss your BMI results and treatment options.