Stone to Kg Converter – Exact Formula, NHS Chart and Guide

Need to convert stones to kilograms quickly and accurately? Whether you are checking your weight for a medical form, calculating your BMI, or simply curious about the metric equivalent of a UK stone measurement, understanding the exact conversion factor is essential. This guide provides the precise formula, answers to the most common conversions like 12 stone in kg, and explains how official NHS charts handle the numbers for clinical use.

How Many Kilograms Are in a Stone? (The Exact Formula)

• 1 stone equals exactly 6.35029318 kg, as defined by UK law.
• The conversion factor comes from the fact that 1 stone is 14 pounds.
• One pound is internationally agreed to weigh 0.45359237 kilograms.
• The most searched individual conversions are 10, 12, 11, and 17 stone.
• Official NHS charts round the result to two decimal places for clinical practicality.
• The stone remains the standard unit for body weight in the UK and Ireland.

The precise formula for converting stones to kilograms is simple: multiply the number of stones by 6.35029318. This figure is not an approximation. It is the exact legal standard, confirmed by international agreement and the UK’s own Weights and Measures Act 1985.

Common Stone to Kilogram Conversions (12 Stone in kg, 10 Stone in kg, 11 Stone in kg)

What is 12 stone in kg?

Twelve stone equals 76.20 kg when rounded to two decimal places, which is the standard used in most medical and commercial settings. The exact calculation is 12 multiplied by 6.35029318, which gives 76.20351816 kg.

What is 10 stone in kg?

Ten stone converts to 63.50 kg. This is one of the most frequently searched conversions, as it represents a common target weight for many individuals. The precise figure is 63.5029318 kg.

What is 11 stone in kg?

Eleven stone is equivalent to 69.85 kg. Exactly, it is 69.85322498 kg.

What is 17 stone in kg?

Seventeen stone is a higher-end conversion often used in clinical weight management. It is equal to 107.95 kg (exact: 107.95498406 kg).

What is 9 stone in kg?

Nine stone comes out to 57.15 kg. The exact number is 57.15263862 kg.

What is 2 stone in kg?

Two stone is approximately 12.70 kg. The precise conversion is 12.70058636 kg.

How to Convert Kilograms (kg) Back to Stones and Pounds

Converting from metric back to imperial is a two-step process. First, divide the kilogram weight by 6.35029318 to get the total number of stones. The whole number of that result is the stone value. The decimal portion must then be multiplied by 14 to find the remaining pounds.

The formula is: stones = kg ÷ 6.35029318. Then, pounds = (total stones – whole stones) × 14.

For a quick reference, a weight of 102 kg is approximately 16 stone and 0.9 pounds. A weight of 104 kg is roughly 16 stone and 5.3 pounds. These examples come from standard conversion tools.

The NHS Weight Conversion Chart: Stones to kg for Medical Use

NHS trusts across the UK rely on official weight conversion charts to ensure accurate patient data. These charts, available as PDFs from sources like UHSussex and the Scottish Community Pharmacy, use the standard conversion factor but present the results in a simple, rounded format suitable for clinical environments.

The NHS Weight Conversion Chart (PDF) published by UHSussex is a primary example. It lists values like 9 stone as 57.15 kg and 10 stone as 63.5 kg. The chart continues to higher values and includes a corresponding height conversion (feet and inches to metres) for BMI calculation. The rounding standard used in these medical charts is two decimal places, prioritizing clarity over extreme precision.

History of the Stone Unit

1. Pre-14th century: The stone was used as a local weighing standard across Europe. Its actual weight varied by location and commodity.
2. 1835: The UK Weights and Measures Act officially standardized the stone at 14 avoirdupois pounds, ending regional variations.
3. 1985: The later Weights and Measures Act retained the stone as a legal unit for specific purposes, including body weight measurement, even as the UK moved toward metrication.

The stone remains a legal unit for trade in the UK, defined by the UK National Measurement Office – Stone unit definition as exactly 6.35029318 kg. This legal definition comes from the international standard for the avoirdupois pound, which is set by the National Institute of Standards and Technology (NIST).

Rounding and Precision: What to Know

Why the Stone Unit Still Matters in the UK

The stone remains the dominant unit for personal body weight in the UK, Ireland, and parts of the Commonwealth, despite the widespread adoption of the metric system. Medical professionals in the UK frequently encounter patients who provide their weight in stones and pounds, making the conversion to kilograms essential for BMI calculations, medication dosing, and official health records. The NHS Weight Conversion Chart (PDF) serves as the de facto clinical standard to ensure consistency across hospital trusts and GP surgeries.

Where Do the Official Conversion Standards Come From?

The authority for the stone to kilogram conversion rests on three pillars. First, the NHS Weight Conversion Chart (PDF) provides the official healthcare reference for rounding and clinical tables. Second, the UK Weights and Measures Act 1985 legally defines the stone as 6.35029318 kg, confirming its use for trade and health. Third, the National Institute of Standards and Technology (NIST) defines the international conversion factor from the pound to the kilogram, upon which the stone value is built.

“The stone is a legal unit of measurement in the UK, exactly equal to 6.35029318 kilograms, as defined by the Weights and Measures Act 1985.”

— UK Weights and Measures Legislation

“Official NHS weight conversion charts use the 6.35029318 factor, rounding the final kilogram value to two decimal places for clinical readability and patient safety.”

— UHSussex NHS Weight Conversion Chart Documentation

Making Your Weight Conversion Future-Proof

For most everyday and medical purposes, using the rounded figures provided by NHS charts is perfectly sufficient. However, for international travel, scientific research, or official medical forms that require strict metric values, always use the exact formula (stones × 6.35029318). You can also use a kg to stone converter for the reverse calculation. For a broader range of imperial and metric weights, consult our full weight conversion table.

Frequently Asked Questions