Weight Unit Converter
BMI Calculator
Ideal Weight Range Calculator
How to Use This Weight Calculator
Weight Conversion
Enter any weight value and select the unit you want to convert from. The calculator will automatically display the equivalent weights in kilograms, pounds, stones, grams, ounces, and tonnes. This is particularly useful in the UK where stones are commonly used alongside metric measurements.
BMI Calculation
Input your height and weight in your preferred units. The calculator converts these measurements and computes your Body Mass Index using the standard formula. Your result will include your BMI value, weight category, and your ideal weight range based on NHS guidelines.
Ideal Weight Range
Simply enter your height to discover the weight range that corresponds to a healthy BMI between 18.5 and 24.9. This range is based on World Health Organisation standards and NHS recommendations.
BMI Categories Explained
| BMI Range (kg/m²) | Category | Health Implications |
|---|---|---|
| Below 18.5 | Underweight | May indicate malnutrition or eating disorders. Increased risk of weakened immunity and osteoporosis. |
| 18.5 – 24.9 | Healthy Weight | Optimal range associated with lower risk of weight-related health conditions. |
| 25 – 29.9 | Overweight | Increased risk of type 2 diabetes, high blood pressure, and cardiovascular disease. |
| 30 – 34.9 | Obese Class I | Moderately increased health risks requiring lifestyle changes. |
| 35 – 39.9 | Obese Class II | Severely increased health risks. Medical intervention may be recommended. |
| 40 and above | Obese Class III | Very high risk of serious health conditions. Medical supervision advised. |
Weight Measurement Systems in the UK
The United Kingdom uses a unique combination of imperial and metric measurements for weight. While official NHS guidelines and medical settings use metric units (kilograms), many people still prefer stones and pounds for personal weight measurements.
Common UK Weight Units
Stone: One stone equals 14 pounds or approximately 6.35 kilograms. This unit remains popular in the UK and Ireland for measuring body weight.
Kilogram: The standard metric unit used in healthcare settings. One kilogram equals 2.205 pounds or approximately 0.157 stones.
Pound: An imperial unit where 1 pound equals 0.453592 kilograms. Commonly used alongside stones in the UK.
| Stones | Kilograms | Pounds |
|---|---|---|
| 8 st | 50.8 kg | 112 lb |
| 10 st | 63.5 kg | 140 lb |
| 12 st | 76.2 kg | 168 lb |
| 14 st | 88.9 kg | 196 lb |
| 16 st | 101.6 kg | 224 lb |
| 18 st | 114.3 kg | 252 lb |
The BMI Formula and Calculation Method
Body Mass Index is calculated by dividing a person’s weight in kilograms by the square of their height in metres. The mathematical formula is expressed as BMI = weight (kg) ÷ height² (m²).
Calculation Example
For someone weighing 70 kilograms with a height of 1.75 metres, the calculation proceeds as follows. First, square the height by multiplying 1.75 by 1.75, which equals 3.0625. Then divide the weight of 70 kilograms by 3.0625, resulting in a BMI of 22.9. This value falls within the healthy weight range of 18.5 to 24.9.
Converting UK Measurements
When your weight is measured in stones and pounds, convert to kilograms by multiplying stones by 6.35029 and pounds by 0.453592, then adding the results. For height in feet and inches, multiply feet by 0.3048 and inches by 0.0254, add these values, then use the resulting metres in the BMI formula.
Limitations of BMI
Athletes and Muscular Individuals: People with high muscle mass may have an elevated BMI despite having low body fat. Muscle tissue is denser than fat, which can result in misleading classifications.
Older Adults: As people age, they typically lose muscle mass and gain fat. BMI may underestimate body fat in elderly individuals, potentially classifying them as healthy weight when body composition suggests otherwise.
Ethnic Variations: Research indicates that people of Asian descent face increased health risks at lower BMI values. The NHS recommends that individuals from Black and Asian backgrounds consult healthcare professionals for personalised assessments.
Pregnancy and Children: BMI calculations are not appropriate during pregnancy due to natural weight gain. Children and teenagers require age-specific centile charts rather than adult BMI categories, as body composition changes significantly during growth and development.
Frequently Asked Questions
Achieving and Maintaining a Healthy Weight
Balanced Nutrition: A varied diet including fruits, vegetables, whole grains, lean proteins, and healthy fats supports weight management. The NHS Eatwell Guide recommends filling half your plate with vegetables and fruits, a quarter with wholegrain carbohydrates, and a quarter with protein sources.
Physical Activity: Adults should aim for at least 150 minutes of moderate aerobic activity or 75 minutes of vigorous activity weekly, plus strength training twice a week. Activities like brisk walking, cycling, swimming, or gardening contribute to calorie expenditure and muscle maintenance.
Portion Control: Using smaller plates, checking food labels, and being mindful of serving sizes helps prevent overeating. Restaurant portions often exceed recommended amounts, so consider sharing meals or saving half for later.
Hydration: Drinking water before meals can reduce appetite and calorie intake. The NHS recommends 6 to 8 glasses of fluid daily, with water being the healthiest choice. Sugary drinks contribute significant calories without providing satiety.
Sleep Quality: Insufficient sleep disrupts hormones that regulate hunger and appetite, potentially leading to weight gain. Adults should aim for 7 to 9 hours of quality sleep per night to support metabolic health.
Professional Support: If you struggle with weight management, NHS services include referrals to dietitians, weight management programmes, and in some cases, specialist obesity services. Your GP can assess your individual circumstances and recommend appropriate interventions.
When to Seek Medical Advice
Consult a healthcare professional if your BMI falls outside the healthy range, especially if you experience related symptoms. Unexplained weight loss or gain, difficulty performing daily activities, breathlessness, joint pain, or signs of nutritional deficiency warrant medical evaluation.
Individuals with pre-existing conditions such as diabetes, cardiovascular disease, or eating disorders require tailored guidance rather than general weight management advice. Pregnant women or those planning pregnancy should discuss weight matters with their midwife or GP.
The NHS provides various weight management services depending on your BMI and circumstances. These range from lifestyle advice and group programmes to specialist clinics for severe obesity. Early intervention typically yields better outcomes and prevents complications.