Calculate weight from mass and gravitational acceleration for physics and engineering use.
This tool provides estimates for informational purposes only. It is not a substitute for professional advice. Individual results vary based on your inputs and assumptions, so review important decisions with a qualified professional.
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Weight conversion is one of the most common everyday calculations — whether you are converting your body weight from kilograms to stone for a UK GP consultation, converting lbs to kg for an international shipping label, checking a recipe that uses US cups and ounces, or understanding vehicle payload limits. This comprehensive guide covers all major weight units, conversion factors, UK and US specific conventions, healthy weight ranges, and practical applications across domestic, commercial, and scientific contexts.
| From | To Kg | To Lbs | To Stone (UK) |
|---|---|---|---|
| 1 kg | 1.000 | 2.2046 | 0.1575 |
| 1 lb | 0.4536 | 1.000 | 0.0714 |
| 1 stone | 6.350 | 14.000 | 1.000 |
| 1 oz | 0.02835 | 0.0625 | 0.00446 |
| 1 gram | 0.001 | 0.002205 | 0.0001575 |
The stone unit (1 stone = 14 pounds = 6.35 kg) is one of the most distinctively British measurement conventions. While the rest of the world uses kilograms for body weight, the UK maintains the stone as the dominant cultural reference for personal weight.
Key stone-to-kg conversions for body weight context:
| Stone and Pounds | Kilograms | Pounds |
|---|---|---|
| 8 stone | 50.8 kg | 112 lbs |
| 9 stone | 57.2 kg | 126 lbs |
| 10 stone | 63.5 kg | 140 lbs |
| 11 stone | 69.9 kg | 154 lbs |
| 12 stone | 76.2 kg | 168 lbs |
| 13 stone | 82.6 kg | 182 lbs |
| 14 stone | 88.9 kg | 196 lbs |
| 15 stone | 95.3 kg | 210 lbs |
| 16 stone | 101.6 kg | 224 lbs |
UK NHS patient records use both kg and stone/lbs for body weight. GPs and hospitals typically weigh patients in kilograms for clinical calculations (drug dosing, BMI) but communicate weight to patients in stone and pounds because that is what most UK adults understand intuitively. This dual-system approach is a uniquely British feature of clinical practice.
Weight depends on gravitational field strength, which varies across the solar system. Mass (measured in kg) remains constant — only weight changes:
| Planet/Body | Gravity (m/s2) | 70 kg Weight (lbs) | 70 kg Weight (stone) |
|---|---|---|---|
| Earth | 9.81 | 154 lbs | 11 stone |
| Moon | 1.62 | 25.5 lbs | 1 st 11 lbs |
| Mars | 3.72 | 58.5 lbs | 4 st 2 lbs |
| Jupiter | 24.79 | 390 lbs | 27 st 12 lbs |
| Saturn | 10.44 | 163 lbs | 11 st 9 lbs |
The World Health Organization (WHO) and NHS use Body Mass Index (BMI) as the primary weight-for-height screening tool. BMI = weight (kg) / height (m)2.
| BMI Range | WHO Category | UK/US Guidance |
|---|---|---|
| Below 18.5 | Underweight | Medical evaluation recommended |
| 18.5–24.9 | Normal weight | Healthy range |
| 25.0–29.9 | Overweight | Lifestyle review advised; NHS weight management |
| 30.0–34.9 | Obese Class I | NHS/CDC intervention recommended |
| 35.0–39.9 | Obese Class II | Medical treatment; possible bariatric referral |
| 40.0+ | Obese Class III (Severe) | Bariatric surgery consideration |
BMI has limitations: it does not distinguish between muscle and fat, underestimates obesity risk in Asian populations (WHO uses lower thresholds of 23.0 for overweight and 27.5 for obese for Asian populations), and is a poor indicator of metabolic health in athletes. The UK NHS currently uses BMI as a primary screening tool but recommends waist circumference as a supplementary measure (healthy: below 94 cm for men, below 80 cm for women in European populations).
Average birth weight varies slightly between countries and populations:
Birth weight conversions: 1 lb = 453.6 g = 0.4536 kg; 1 oz = 28.35 g. So 7 lbs 8 oz = (7 x 453.6) + (8 x 28.35) = 3175 + 226.8 = 3402 g = 3.40 kg.
Commercial and postal shipping distinguishes between three weight measures:
UK Trading Standards and US FDA/USDA regulations both require net weight declarations on pre-packaged food. The UK Weights and Measures Act 1985 specifies tolerances for short-weight enforcement. Under the Measuring Instruments Regulations 2016 (UK post-Brexit retained EU law), all commercial weighing instruments must be type-approved and verified.
Building and civil engineers distinguish load types by weight characteristics:
UK floor loading limits are important for domestic settings too — a standard UK residential floor is typically designed for 1.5 kN/m2 (153 kg/m2). A standard household safe, heavy aquarium, or grand piano can approach or exceed this in concentrated areas.
| Scale Type | Typical Accuracy | UK/US Use |
|---|---|---|
| Bathroom scale | +/- 100–500 g | Body weight (UK shows kg/stone; US shows lbs) |
| Kitchen scale | +/- 1–5 g | Food preparation (UK uses grams; US uses oz/cups) |
| Postal scale | +/- 1–2 g | Letter and parcel weight for postage calculation |
| Laboratory balance | +/- 0.001 g (1 mg) | Scientific research, pharmaceutical compounding |
| Platform/pallet scale | +/- 100 g to 1 kg | Freight, shipping, industrial weighing |
Divide kilograms by 6.35 to get the stone component. Multiply the decimal part by 14 to get the remaining pounds. For example, 75 kg / 6.35 = 11.81 stone = 11 stone + (0.81 x 14) = 11 stone 11.3 lbs. Alternatively, multiply kg by 2.2046 to get total pounds, then divide by 14 to get stone with remainder in pounds.
Multiply pounds by 0.4536 to get kilograms. For example, 150 lbs x 0.4536 = 68.0 kg. To convert kg to lbs, multiply by 2.2046. A quick mental estimate: divide pounds by 2.2 for a close approximation (150 / 2.2 = 68.2 kg).
The NHS and WHO use BMI (weight in kg / height in metres squared) to assess healthy weight. BMI 18.5–24.9 is healthy. A 175 cm person with healthy BMI weighs approximately 57–76 kg (9 to 12 stone). BMI has limitations and waist circumference (under 94 cm for men, under 80 cm for women) is a useful supplementary measure.
According to the Health Survey for England, the average weight of an English adult man is approximately 83.9 kg (13 stone 3 lbs) and women 70.2 kg (11 stone 1 lb). Average BMI for men is 27.4 (overweight range); for women 26.6. US averages are higher: approximately 90.6 kg for men and 77.2 kg for women according to CDC NHANES data.
Net weight is the weight of the product alone, excluding packaging. Gross weight is the total weight including all packaging. Tare weight is the weight of the empty container. Gross = Net + Tare. All pre-packaged food in the UK (under Weights and Measures legislation) must declare net weight, and short-weight enforcement applies.
The average UK newborn weight is approximately 3.4 kg (7 lbs 8 oz). The average US newborn weighs approximately 3.32 kg (7 lbs 5 oz). Low birth weight (below 2.5 kg / 5 lbs 8 oz) is associated with increased health risk. High birth weight (above 4.0 kg / 8 lbs 13 oz) may indicate gestational diabetes and is monitored closely by UK midwives and US obstetricians.
Multiply ounces by 28.3495 to get grams. For example, 8 oz x 28.35 = 226.8 g. Conversely, divide grams by 28.35 to get ounces. A quick approximation: 1 oz is close to 30 g (slightly less). Note that troy ounces (used for precious metals) are different from avoirdupois ounces: 1 troy oz = 31.1 g.
Standard UK residential floors are typically designed for 1.5 kN/m2 (approximately 150 kg per square metre) as a distributed load. Point loads — like the legs of a heavy safe, fish tank, or grand piano — can create concentrated stress exceeding this. A 200 litre aquarium weighs approximately 220 kg when full. If placing very heavy objects, consult a structural engineer to assess your specific floor construction.