BMI Calculator
Enter your height and weight in metric or imperial units to get your BMI and where it sits in the standard adult ranges — underweight, healthy, overweight or obese.
How it works
BMI = weight in kilograms ÷ (height in metres)². Someone who is 5ft 9in (1.75 m) and 12st 8lb (80 kg) has a BMI of 80 ÷ 3.0625 = 26.1.
Standard adult categories (WHO): under 18.5 underweight · 18.5–24.9 healthy · 25–29.9 overweight · 30–34.9 obese (class I) · 35–39.9 obese (class II) · 40+ obese (class III).
Imperial entries are converted first: 1 stone = 6.35029 kg, 1 inch = 2.54 cm. BMI is a screening measure — it ignores muscle mass, age and waist size, so borderline results deserve a proper health check rather than a self-diagnosis.
FAQ
What is a healthy BMI in the UK?
For most adults a BMI of 18.5 to 24.9 is considered the healthy range. NHS guidance also notes that people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean backgrounds face higher health risks at lower BMIs, with an overweight threshold of 23 rather than 25 — so the standard bands are not one-size-fits-all.
What weight should I be for my height?
Multiply your height in metres squared by 18.5 and 24.9 to get the healthy band. At 5ft 6in (1.68 m) that is 18.5 × 2.82 ≈ 52 kg (8st 3lb) to 24.9 × 2.82 ≈ 70 kg (11st), and the calculator shows this range automatically for the height you enter. Aim for somewhere inside the band rather than a single “ideal” number.
Is BMI accurate if I train with weights?
It can overstate fatness in muscular people: muscle is denser than fat, so a rugby player or regular lifter can have a BMI over 25 with low body fat. BMI is designed as a population screening tool, not an individual diagnosis — waist measurement, body-fat percentage and a GP’s assessment give a much better picture for athletic builds.