Convert stone and pounds to kilograms instantly. Includes a bidirectional converter, full conversion table, and BMI guidance for UK users.
The stone is a unit of weight primarily used in the United Kingdom and Ireland for measuring human body weight. While the metric system has been officially adopted throughout the UK, stones and pounds remain deeply embedded in everyday language when people describe how much they weigh. Your GP may record your weight in kilograms, but most British people still think of their body weight in stones.
Understanding how to convert between stones and kilograms is essential for anyone tracking their fitness, interpreting NHS health guidelines, or communicating with healthcare professionals who use different measurement systems.
The conversion between stones and kilograms is based on the following chain of definitions:
This is an exact conversion defined by international agreement. When you see stones converted to kilograms, it should always use 6.35029 as the multiplication factor for maximum precision.
To convert a weight given in stones and pounds to kilograms, use this formula:
For example, if you weigh 11 stone 7 pounds:
| Stone | Kilograms (kg) | Pounds (lbs) | BMI at 5'6" (1.68m) |
|---|
The United Kingdom officially adopted the metric system for trade and official measurements decades ago, yet stones remain the dominant unit for personal body weight among the general public. This cultural persistence is unique — most other countries that have metricated dropped imperial units entirely for everyday use, but the British stone has proven remarkably resilient.
The reason is largely generational and habitual. Most adults in the UK grew up hearing their parents' weight described in stones. School health checks recorded weights in stones and pounds. Even television programmes discussing weight loss tend to use stones. The unit simply feels natural and intuitive to most British people in a way that kilograms still do not, despite decades of official metrication.
The NHS officially records and uses kilograms for all clinical purposes. When you attend a GP appointment, your weight will be recorded in kilograms. NHS drug dosing, BMI calculations, and clinical assessments all use the metric system. When the NHS provides healthy weight ranges, these are expressed in kilograms and BMI values.
However, many healthcare professionals will helpfully provide a stone equivalent when telling patients their weight, because they understand the emotional and conceptual connection most patients have with the imperial system. If your GP says you need to lose weight, they might say "you need to lose about a stone" rather than "you need to lose 6.35 kilograms" — even though both mean the same thing.
The NHS defines a healthy BMI as between 18.5 and 24.9. The weight range that represents a healthy BMI varies by height. Here are healthy weight ranges for common heights expressed in both units:
| Height | Healthy Weight Range (kg) | Healthy Weight Range (stone) |
|---|---|---|
| 5'4" (1.63m) | 49.2 – 66.0 kg | 7st 10lb – 10st 5lb |
| 5'6" (1.68m) | 52.2 – 70.3 kg | 8st 3lb – 11st 1lb |
| 5'8" (1.73m) | 55.4 – 74.5 kg | 8st 10lb – 11st 10lb |
| 5'10" (1.78m) | 58.7 – 78.9 kg | 9st 3lb – 12st 6lb |
| 6'0" (1.83m) | 62.1 – 83.6 kg | 9st 11lb – 13st 2lb |
| 6'2" (1.88m) | 65.7 – 88.5 kg | 10st 5lb – 13st 13lb |
BMI (Body Mass Index) is calculated as weight in kilograms divided by height in metres squared. Because BMI is a metric formula, you need to convert your weight to kilograms first if you know it in stones. Our calculator above handles this automatically, but here is the process step by step:
The BMI overweight threshold of 25 corresponds to approximately 70 kg for a person who is 5'6" (1.68m) tall — roughly 11 stone. For someone who is 5'10" (1.78m), the overweight threshold rises to approximately 79 kg (about 12 stone 6 lbs).
It is important to note that BMI is a screening tool, not a diagnostic tool. It does not account for muscle mass, bone density, age, sex, or ethnic background. The NHS and NICE recommend using waist circumference alongside BMI for a more complete picture of health risk. For people of South Asian, Chinese, or other East Asian descent, the NHS applies lower BMI thresholds for overweight and obesity classification.