Pounds to Kilograms Converter

International Mass Metrology & The 0.45359237 Invariant (1959)

The avoirdupois pound (lb) and kilogram (kg) are locked by international treaty:

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• Exact Defining Invariant**:

1 lb 0.45359237 kg Exact 1 kg = (1) / (0.45359237) lbs ≈ 2.2046226218 lbs

Kilograms (kg) = Pounds (lbs) × 0.45359237

Pounds (lbs) = Kilograms0.45359237 ≈ Kilograms × 2.20462262

• **

• British Stone Metrology**:

1 Stone (st) 14 lbs = 6.35029318 kg

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• Standard Clinical & Weight Benchmarks**:

• 1.0 lb = 0.4536 kg = 453.59 g = 16.00 oz

• 5.0 lbs = 2.2680 kg = 2,267.96 g

• 50.0 lbs (Airline Bag) = 22.6796 kg = 3 st 8.0 lbs

• 70.0 kg (WHO Adult) = 154.3236 lbs = 11 st 0.32 lbs

• 150.0 lbs = 68.0389 kg = 10 st 10.0 lbs

• 200.0 lbs = 90.7185 kg = 14 st 4.0 lbs

How to Use This Calculator

Enter your Mass / Bodyweight Value (e.g. 150), Conversion Direction — choose from Pounds (lbs) to Kilograms (kg = lbs × 0.45359237), Kilograms (kg) to Pounds (lbs = kg ÷ 0.45359237), and Clinical & Fitness Benchmark — choose from Custom Mass Value, 150.0 lbs (Human Adult Weight) → 68.0389 kg (10 st 10.0 lbs), 1.0 lb Standard → 0.4536 kg (16.0 oz / 453.59 g). Results update instantly as you type — adjust any value to compare scenarios.

The Formula

Conversion factors used in this calculator:

1 lb = 0.45359237 kg exact

Worked Example

A clinician calculating an antibiotic dose for a 150-pound patient converts bodyweight into metric units as 150 × 0.45359237 = 68.0389 kg for hospital charting.

Understanding Your Result

Unit conversion precision: round to the same number of significant figures as your original measurement. Converting 6 feet to meters gives 1.8288 m — but if your measurement was approximate (±1 inch), expressing more than 2 decimal places is false precision. For international trade and technical specifications, SI units (meters, kilograms, liters) are the standard. US customary units (feet, pounds, gallons) differ from Imperial UK units: 1 US gallon = 3.785 L vs. 1 UK gallon = 4.546 L.