Lbs to Kg Calculator
Convert pounds to kilograms, kilograms to pounds, and see body weight in stone. Also convert ounces to grams. 1 lb = 0.453592 kg exactly — used by the NHS, gyms, and boxers worldwide.
Lbs to Kg Conversion Table (100–300 lbs)
| Lbs | Kg | Stone & lbs | BMI (5'8" / 173 cm) |
|---|---|---|---|
| 100 | 45.36 kg | 7 st 2 lb | 15.3 |
| 110 | 49.90 kg | 7 st 12 lb | 16.7 |
| 120 | 54.43 kg | 8 st 8 lb | 18.2 |
| 130 | 58.97 kg | 9 st 4 lb | 19.7 |
| 140 | 63.50 kg | 10 st 0 lb | 21.2 |
| 150 | 68.04 kg | 10 st 10 lb | 22.7 |
| 160 | 72.57 kg | 11 st 6 lb | 24.2 |
| 170 | 77.11 kg | 12 st 2 lb | 25.7 |
| 180 | 81.65 kg | 12 st 12 lb | 27.2 |
| 190 | 86.18 kg | 13 st 8 lb | 28.7 |
| 200 | 90.72 kg | 14 st 4 lb | 30.2 |
| 220 | 99.79 kg | 15 st 12 lb | 33.3 |
| 250 | 113.40 kg | 17 st 12 lb | 37.8 |
| 300 | 136.08 kg | 21 st 6 lb | 45.3 |
BMI shown for reference at height 5'8" (173 cm). BMI = kg ÷ (height in metres)².
The Pound: History and Definition
The pound (lb) is one of the oldest units of weight in continuous use in Britain, with roots going back to the Roman libra pondo (pound weight) — which is why both "lb" (the abbreviation) and "£" (the currency symbol) derive from the Latin libra. Over centuries, several different pounds were used in Britain: the Tower pound, the Troy pound, the Merchant pound, and the Avoirdupois pound.
Today's pound is the avoirdupois pound, internationally defined since 1959 as exactly 0.45359237 kilograms. This definition was agreed by the United States, Canada, Australia, New Zealand, South Africa, and the United Kingdom in the International Yard and Pound Agreement of 1959. It replaced earlier, slightly varying national definitions.
Body Weight in the UK: Stone, Lbs, and Kg
The UK has a unique relationship with body weight measurement. Officially, the NHS uses kilograms for all clinical purposes. BMI calculations, drug dosing by body weight, and nutritional assessments are all in metric. Yet informally, most British adults describe their weight in stones and pounds — a system that does not exist in the US (which uses only pounds) or in most of Europe (which uses only kilograms).
This creates genuine confusion. A British person who weighs 11 stone might not immediately know that this equals:
- 154 pounds (11 × 14 = 154)
- 69.85 kilograms (154 × 0.453592)
When visiting an NHS clinic, patients are typically weighed in kilograms on clinical scales. The doctor calculates BMI using kilograms and height in metres. But the patient goes home and tells their family they weigh "11 stone" — none of the three measurement systems quite aligning in everyday British health conversations.
Gym Weights: Lbs vs Kg Plates
UK gyms typically use metric (kg) weight plates, but many exercises and personal bests are still discussed in pounds among gym-goers influenced by American fitness culture. Here is a practical reference for common barbell configurations:
| Plates Each Side | Total Weight (kg) | Total Weight (lbs) | Common Use |
|---|---|---|---|
| 2 × 5 kg | 30 kg (bar 20 kg) | 66.1 lbs | Beginner squat/deadlift |
| 2 × 10 kg | 40 kg (bar 20 kg) | 88.2 lbs | Light press/row |
| 2 × 20 kg | 60 kg (bar 20 kg) | 132.3 lbs | Intermediate bench press |
| 2 × 20 + 2 × 5 kg | 70 kg (bar 20 kg) | 154.3 lbs | Common deadlift starting weight |
| 2 × 40 kg | 100 kg (bar 20 kg) | 220.5 lbs | "100 kg club" milestone |
| 2 × 50 kg + 2 × 10 kg | 140 kg (bar 20 kg) | 308.6 lbs | Advanced powerlifting |
The American "plate" (45 lbs = 20.41 kg) is very close to the 20 kg metric plate (44.09 lbs), which is why both cultures effectively train with the same real load while using different numbers. A US lifter boasting a "315 lb bench" has lifted 142.9 kg — equivalent to 7 standard 20 kg plates plus the bar.
Boxing Weight Classes in Lbs and Kg
Boxing weight categories were originally defined in pounds and remain standardised in pounds by most governing bodies, though the British Boxing Board of Control (BBBofC) and European bodies now use both. Here are the main professional boxing weight classes:
| Weight Class | Max Weight (lbs) | Max Weight (kg) | Max Weight (stone) |
|---|---|---|---|
| Strawweight / Mini Flyweight | 105 lbs | 47.6 kg | 7 st 7 lb |
| Flyweight | 112 lbs | 50.8 kg | 8 st 0 lb |
| Bantamweight | 118 lbs | 53.5 kg | 8 st 6 lb |
| Featherweight | 126 lbs | 57.2 kg | 9 st 0 lb |
| Lightweight | 135 lbs | 61.2 kg | 9 st 9 lb |
| Welterweight | 147 lbs | 66.7 kg | 10 st 7 lb |
| Middleweight | 160 lbs | 72.6 kg | 11 st 6 lb |
| Light Heavyweight | 175 lbs | 79.4 kg | 12 st 7 lb |
| Heavyweight | 200+ lbs | 90.7+ kg | 14 st 4 lb+ |
Baby Birth Weight: Lbs/Oz vs Kg
In the UK, baby birth weights are officially recorded in grams and kilograms by the NHS. A healthy full-term newborn typically weighs between 2.5 kg (5 lbs 8 oz) and 4.5 kg (9 lbs 14 oz), with the average being approximately 3.3 kg (7 lbs 4 oz).
Despite official metric recording, British parents almost universally remember and share their babies' birth weights in pounds and ounces. "She was 7 pounds 6 ounces" is the typical British announcement — not "3.34 kilograms." This cultural habit has persisted even as the generation of parents grew up with metric education in schools.
Common UK birth weight reference points:
- Low birth weight: under 2.5 kg (5 lbs 8 oz)
- Average birth weight: 3.3 kg (7 lbs 4 oz)
- Large for gestational age: over 4 kg (8 lbs 13 oz)
- Macrosomia (very large baby): over 4.5 kg (9 lbs 14 oz)
Olympic Weightlifting: Kg Only
Olympic weightlifting uses kilograms exclusively and has since the early 20th century. The 2020 Tokyo Olympic weightlifting categories for men were: 61 kg, 67 kg, 73 kg, 81 kg, 89 kg, 96 kg, 102 kg, 109 kg, and +109 kg. For women: 49 kg, 55 kg, 59 kg, 64 kg, 71 kg, 76 kg, 81 kg, 87 kg, and +87 kg.
For British viewers used to thinking in stone and pounds, the 81 kg category corresponds to approximately 12 stone 11 lbs, and the 109 kg category corresponds to about 17 stone 2 lbs.
Related Calculators
- Stone to Lbs Calculator
- BMI Calculator
- Gallons to Litres Calculator
- Inches to Feet Calculator
- Pints to Litres Calculator
Frequently Asked Questions
One pound (lb) is exactly 0.45359237 kilograms. This precise value was agreed internationally in 1959. For practical purposes, use 0.453592 kg per pound. To convert any pounds figure to kilograms, multiply by 0.453592. For example: 10 lbs = 4.536 kg; 100 lbs = 45.36 kg; 200 lbs = 90.72 kg; 300 lbs = 136.08 kg.
There are exactly 14 pounds in one stone. So to convert stone to pounds, multiply by 14. To convert stone and pounds to kg: multiply the total pounds by 0.453592. Example: 11 stone 4 lbs = (11 × 14) + 4 = 158 lbs = 158 × 0.453592 = 71.67 kg. The stone is unique to the UK and Ireland; the US uses only pounds for body weight.
150 pounds equals 68.039 kg (150 × 0.453592 = 68.039). In stone and pounds, 150 lbs = 10 stone 10 lbs (10 × 14 = 140, remainder 10). At a height of 5'8" (173 cm), a weight of 150 lbs / 68 kg gives a BMI of approximately 22.7, which is within the healthy range of 18.5–24.9.
The NHS officially uses kilograms for all clinical measurements including BMI calculations, drug dosing (many medicines are dosed per kg body weight), and nutritional assessments. Patient records store weight in kg and height in cm/metres. However, NHS patient-facing materials and many NHS staff are comfortable with stones and pounds, and some online NHS tools show both metric and imperial. Baby weights are officially recorded in grams/kg, though parents typically describe them in lbs and oz.
There are exactly 16 ounces in one avoirdupois pound. Since 1 lb = 453.592 grams, 1 ounce = 453.592 ÷ 16 = 28.3495 grams. This is the ounce used for everyday weight measurement (not the troy ounce of 31.1035 grams used for precious metals). So 8 oz = 226.8 grams; 12 oz = 340.2 grams; 16 oz = 453.6 grams (1 lb).
According to NHS and ONS data, the average UK adult weight is approximately 83.6 kg (184 lbs / 13 stone 2 lbs) for men and approximately 70.2 kg (155 lbs / 11 stone 1 lb) for women. Average UK adult height is 175.3 cm (5'9") for men and 161.6 cm (5'3.6") for women. These averages have increased significantly since the 1990s due to rising rates of overweight and obesity.
The average UK full-term newborn weighs approximately 3.3 kg (7 lbs 4 oz). The normal range is 2.5 kg to 4.5 kg (5 lbs 8 oz to 9 lbs 14 oz). Babies under 2.5 kg are classed as low birth weight and receive additional monitoring. Despite NHS official recording in grams and kg, British parents almost universally describe birth weights in lbs and oz. "7 lb 6 oz" is a typical birth announcement weight in the UK.