terican

BIPM-ratified constants · v1.0

Converter

Stones, to kilograms converter calculator.

Convert stones to kilograms using the precise formula kg = st x 6.35029318. Fast, accurate stones to kg converter for health and fitness use.

From

stones

st_to_kg

1 st_to_kg =6.3503Kilograms

Equivalents

Precision: 6 dp · Notation: Decimal · 2 units

→ Kilograms

Stonesst_to_kg6.3503

→ Stones

Kilogramskg_to_st0.15747

Common pairings

1 st_to_kgequals0.15747 kg_to_st
1 kg_to_stequals6.3503 st_to_kg

The conversion

How the value
is computed.

Stones to Kilograms: Formula, Derivation, and Applications

The stones to kg converter transforms mass measurements between the imperial stone unit and the metric kilogram. The stone remains widely used in the United Kingdom and Ireland for expressing human body weight, while the kilogram serves as the globally recognized SI base unit of mass. Accurate conversion between these units relies on a precise, internationally defined factor.

The Conversion Formula

The formula to convert stones to kilograms is:

kg = st × 6.35029318

To convert kilograms back to stones, the inverse formula applies:

st = kg ÷ 6.35029318

Where st represents the mass in stones and kg represents the equivalent mass in kilograms.

Variable Definitions

  • st (stones): The input value in stones. One stone equals exactly 14 avoirdupois pounds by definition.
  • kg (kilograms): The result in kilograms, the SI base unit of mass as maintained by international standards bodies.
  • 6.35029318: The exact conversion factor representing the number of kilograms in one stone, derived from fixed international pound and stone definitions.

Historical Context and Unit Origin

The stone unit originated in medieval England and Scotland as a practical measurement for trade, agriculture, and commerce. Its definition evolved over centuries, eventually standardizing to exactly 14 avoirdupois pounds. Despite metrication efforts across Europe and the Commonwealth nations, the stone persisted in British and Irish culture for personal body weight measurement, creating a unique measurement landscape where clinical records, fitness discussions, and everyday conversations routinely reference this imperial unit alongside metric standards. Understanding this historical persistence helps explain why the conversion between stones and kilograms remains a frequently needed calculation in modern contexts.

Derivation of the Conversion Factor

The conversion factor of 6.35029318 kg per stone derives from two internationally defined relationships. First, one stone equals exactly 14 avoirdupois pounds. Second, one international pound equals exactly 0.45359237 kilograms, established by the international yard and pound agreement of 1959. Multiplying these two values yields: 14 × 0.45359237 = 6.35029318 kg.

This factor is fully traceable to SI base units. According to NIST's SI Units reference, the kilogram is the SI base unit for mass, and all derived conversion factors for traditional units such as the stone must trace back to this standard. Additionally, NIST's documentation on units outside the SI confirms that the international pound value of 0.45359237 kg is exact and universally accepted, ensuring that stones-to-kilograms conversions produce results consistent with international measurement standards.

Practical Conversion Examples

The following examples illustrate common body weight conversions using the formula kg = st × 6.35029318:

  • 8 stone to kg: 8 × 6.35029318 = 50.80 kg
  • 10 stone to kg: 10 × 6.35029318 = 63.50 kg
  • 11 stone to kg: 11 × 6.35029318 = 69.85 kg
  • 12 stone to kg: 12 × 6.35029318 = 76.20 kg
  • 13 stone to kg: 13 × 6.35029318 = 82.55 kg
  • 15 stone to kg: 15 × 6.35029318 = 95.25 kg

For reverse conversions: 60 kg ÷ 6.35029318 = 9.45 st; 75 kg ÷ 6.35029318 = 11.81 st; 100 kg ÷ 6.35029318 = 15.75 st.

Real-World Use Cases

The stones to kilograms converter supports a wide range of practical applications:

  • Clinical and medical settings: UK healthcare providers traditionally record patient weight in stones, while international drug dosing protocols use kilograms. Accurate conversion ensures safe pharmaceutical dosing, where weight-based calculations commonly express dose in mg per kg of body weight.
  • Body mass index (BMI) calculations: BMI requires weight in kilograms and height in meters (BMI = kg / m²). Individuals who know their weight in stones must convert to kg before calculating BMI accurately.
  • Fitness and athletic training: Personal trainers and nutritionists across the UK and internationally translate client weight measurements to ensure consistent tracking, progress monitoring, and macronutrient target setting.
  • Combat sports and weight classes: Boxing, wrestling, and mixed martial arts organizations define weight categories in both stones and kilograms depending on the governing body and country, requiring reliable conversion for competition preparation.
  • Occupational health and safety: Workplace ergonomics assessments, load-bearing equipment specifications, and occupational medicine evaluations may reference weight in either unit depending on regulatory jurisdiction, requiring accurate cross-unit translation.

Precision and Rounding

The conversion factor 6.35029318 carries nine significant figures, matching the precision of the defined international pound (0.45359237 kg). For everyday body weight applications, rounding to two decimal places (6.35 kg per stone) introduces an error of less than 0.005%, negligible for health and fitness purposes. Scientific, legal, and commercial weighing applications should retain the full factor to satisfy metrological traceability requirements and regulatory compliance with international measurement standards.

Reference

Frequently asked questions

How many kg is 1 stone?
One stone equals exactly 6.35029318 kilograms. This value derives from the definition that one stone equals 14 avoirdupois pounds, and one international pound equals exactly 0.45359237 kg. Multiplying 14 by 0.45359237 yields 6.35029318 kg, a factor recognized by NIST and international measurement standards bodies worldwide.
How do you convert stones to kilograms?
To convert stones to kilograms, multiply the stone value by 6.35029318. For example, 11 stone equals 11 times 6.35029318, which gives 69.85 kg. For the reverse conversion, divide the kilogram value by 6.35029318. For instance, 80 kg divided by 6.35029318 equals approximately 12.60 stone.
What is 10 stone in kg?
10 stone equals 63.50 kilograms. Using the formula kg = st times 6.35029318, multiplying 10 by 6.35029318 gives exactly 63.5029318 kg, which rounds to 63.50 kg. This weight falls within the healthy BMI range for many adults of average height, typically corresponding to a BMI of approximately 21 to 23 depending on height.
Why is stone still used in the UK for body weight?
The stone persists in the UK for body weight due to long-established cultural tradition dating back centuries. While the UK officially adopted the metric system for most commercial and scientific purposes, informal body weight discussion in stones remains deeply embedded in everyday life, media coverage, and healthcare conversations. The unit is rarely used outside the UK and Ireland.
How accurate is the stones to kg conversion factor?
The conversion factor 6.35029318 is accurate to nine significant figures, derived from the precisely defined international pound (0.45359237 kg) and the fixed definition of one stone as 14 pounds. For body weight purposes, rounding to 6.35 introduces an error of less than 0.005%. Legal metrology and scientific applications should use the full factor as specified by NIST standards.
What is 70 kg in stone?
70 kilograms equals approximately 11.02 stone. Dividing 70 by the conversion factor 6.35029318 gives 11.0229 stone. This is often expressed as 11 stone and approximately 0.3 pounds when using mixed units. A weight of 70 kg falls within the healthy BMI range for adults of average height according to standard international health guidelines.