BMI Calculator
Calculate your Body Mass Index, see your healthy weight range, and understand your result.
Waist-to-Hip Ratio Calculator
A more precise measure of abdominal fat and cardiovascular risk
For men, a ratio above 0.90 indicates central obesity. Your ratio of 0.86 is approaching increased risk.
What is BMI (Body Mass Index)?
Body Mass Index (BMI) is a numerical value calculated from your weight and height. It's one of the most widely used screening tools in medicine for estimating whether a person's weight falls within a healthy range. Healthcare providers across UK and worldwide use BMI as a quick, initial indicator of potential weight-related health risks. It applies to adult men and women.
How is BMI calculated?
The BMI formula divides your weight in kilograms by your height in metres squared:
For example, if you weigh 75 kg and are 1.73 m tall: 75 ÷ (1.73 × 1.73) = 75 ÷ 2.99 = 25.1 — just into the overweight category according to WHO classifications. If you're using imperial measurements, the formula is: BMI = (weight in pounds ÷ height in inches²) × 703
BMI Categories & Health Risks
BMI in UK - Key statistics
The UK has one of the highest rates of overweight and obesity in Western Europe, and understanding where the country stands can help put your own BMI result into context.
If your BMI places you in the overweight or obese range, you're far from alone in the UK, but it does mean taking your result seriously. Speaking with a GP is a sensible next step, and if weight-related health issues are affecting your ability to work, you may be entitled to Statutory Sick Pay (SSP) under UK employment law.
Limitations of BMI
💪 It can't tell muscle from fat
The core limitation of BMI is that it measures weight relative to height, nothing more. It doesn't distinguish between muscle mass, bone density, water retention, and body fat. Two people with identical BMI scores can have vastly different body compositions and health profiles. Someone carrying most of their weight as lean muscle is in a fundamentally different position to someone carrying it as visceral fat around the abdomen.
👥 It varies by sex, age, and ethnicity
BMI doesn't account for natural differences in body composition across different groups. Women typically carry around 10% more body fat than men at the same BMI, largely due to essential fat stores related to reproductive function. Older adults tend to have less muscle and more fat than younger people at the same BMI. Ethnicity matters too. Research shows that people of South Asian, Chinese, and other Asian backgrounds face elevated health risks at lower BMI thresholds.
🏃 When BMI is least reliable?
Athletes and highly active people often register as overweight or even obese on the BMI scale purely because muscle is denser than fat. Pregnant and breastfeeding women undergo substantial changes in body composition, increased blood volume, fluid retention, and the weight of the growing baby all inflate BMI readings in ways that have nothing to do with excess body fat. Children and teenagers grow at different rates, and their body fat levels change naturally with age and puberty. Standard adult BMI categories don't apply. Instead, the CDC recommends using age- and sex-specific BMI percentile charts for anyone between the ages of 2 and 20. Older adults who have lost muscle mass with age may show a "normal" BMI while actually carrying excess fat, a condition sometimes called sarcopenic obesity. Some research suggests that a slightly higher BMI, between 25 and 27, may actually be associated with better outcomes in adults over 65.
📏 Better measures to use alongside BMI
Waist circumference is one of the most practical alternatives. It specifically measures abdominal fat, which is more closely linked to cardiovascular disease and type 2 diabetes than overall weight. The HSE and WHO recommend the following thresholds for increased health risk: greater than 94 cm (37 inches) for men and greater than 80 cm (32 inches) for women. A substantially increased risk applies above 102 cm (40 inches) for men and 88 cm (35 inches) for women. Waist-to-hip ratio compares waist measurement to hip measurement and provides further insight into fat distribution. A ratio above 0.90 for men or 0.85 for women indicates central obesity according to the WHO. Body fat percentage measures the actual proportion of your weight that comes from fat, making it more precise than BMI. It can be assessed through methods ranging from skinfold callipers to DEXA scans, though these aren't as readily available as a simple BMI calculation.