BMI Calculator
Stone, KG & Pounds
Calculate your Body Mass Index instantly. Enter your details below.
Your BMI
BMI Scale
Important Disclaimer
This is a reference tool only. BMI is one metric among many. For personalized health guidance, consult your GP or healthcare provider.
What Is BMI?
BMI stands for Body Mass Index — a mathematical calculation based on your height and weight.
The formula:
BMI = Weight (kg) ÷ Height² (m)
If you weigh yourself in stones, this calculator converts your reading to kilograms automatically before calculating your BMI.
BMI Reference Categories
| BMI Range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy range |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obese |
Healthy Weight by Height
Weight ranges for a BMI of 18.5–24.9. Select your height:
Normal Weight Range (BMI 18.5–24.9)
52.2 kg — 70.3 kg
(8 st 3 lb — 11 st 1 lb)
| Height | Min (BMI 18.5) | Max (BMI 24.9) |
|---|---|---|
| 5ft 0in | 42.7 kg (6 st 10 lb) | 57.2 kg (9 st 0 lb) |
| 5ft 2in | 45.6 kg (7 st 2 lb) | 61.2 kg (9 st 9 lb) |
| 5ft 4in | 49.2 kg (7 st 10 lb) | 66.0 kg (10 st 5 lb) |
| 5ft 6in ★ | 52.2 kg (8 st 3 lb) | 70.3 kg (11 st 1 lb) |
| 5ft 8in | 55.4 kg (8 st 10 lb) | 74.4 kg (11 st 10 lb) |
| 5ft 10in | 58.6 kg (9 st 3 lb) | 78.7 kg (12 st 5 lb) |
| 6ft 0in | 62.0 kg (9 st 11 lb) | 83.4 kg (13 st 2 lb) |
| 6ft 2in | 65.4 kg (10 st 4 lb) | 87.9 kg (13 st 12 lb) |
Quick BMI — 5ft 6in Reference
At the UK average height of 5ft 6in, use this table without calculating:
| Weight | BMI | Category |
|---|---|---|
| 8 st (50.8 kg) | 18.1 | Underweight |
| 9 st (57.2 kg) | 20.4 | Normal |
| 10 st (63.5 kg) | 22.6 | Normal |
| 11 st (69.9 kg) | 24.9 | Normal |
| 12 st (76.2 kg) | 27.2 | Overweight |
| 14 st (88.9 kg) | 31.7 | Obese |
BMI Limitations
BMI does not directly measure body fat, fitness, or health status. It has well-documented limitations:
Athletes
Muscle weighs more than fat. A fit person with low body fat can register as overweight on BMI.
Muscle densityOlder Adults
Muscle reduces with age and is replaced by fat. A healthy BMI might hide an unhealthy body composition.
Age-related lossPregnancy
BMI is not applicable during pregnancy. Weight gain is normal and expected.
Use pregnancy calcEthnic Groups
South Asian and other ethnic backgrounds face different health risks at the same BMI.
Genetic differencesHeight Extremes
BMI overestimates risk in very tall people and underestimates it in very short ones.
Math limitationsFrequently Asked Questions
Yes. Because muscle weighs more than fat, athletes and very muscular individuals often fall into the overweight or obese categories on a BMI chart despite having low body fat and excellent health.
BMI can be less accurate for older adults. As people age, muscle mass naturally decreases and is replaced by fat. An older person might have a 'healthy' BMI while carrying disproportionately high active fat.
No. BMI does not apply during pregnancy. Weight gain is expected and necessary for fetal development, the placenta, fluid, and changes to your own body. Use our Pregnancy Weight Gain Calculator instead.
Some UK guidance uses lower BMI thresholds for South Asian and certain other ethnic groups because health risks can occur at a lower BMI. Ask a GP which thresholds are relevant to you.
Waist circumference measures abdominal fat. Fat stored around the organs (visceral fat) carries higher health risks than fat stored elsewhere. It is an excellent complementary measure to your BMI.
The BMI mathematical formula (weight ÷ height squared) tends to underestimate health risks in short people and overestimate them in tall people. This is a known limitation of the metric.
Technically yes, according to the standard chart. However, your individual health cannot be determined by a single number. Body composition, lifestyle, ethnicity, and waist size all play a part.
Our calculator multiplies your input in stones by 6.35029 to get kilograms, then divides that by your height in metres squared using the standard BMI formula.
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Medical Disclaimer: Content is for informational purposes only and does not constitute medical advice. Consult your GP for personalized health guidance.