Convert pound to kilogram.

About this conversion

Pounds-to-kilograms: divide by 2.20462 (or multiply by 0.45359237). Used constantly when reading product specs, fitness metrics, medical dosing, and international shipping weights.

Formula

kg = lb × 0.453592

Real-world examples

Reference values

Tips & tricks

• Mental shortcut: divide by 2.2. 100 lb ≈ 45 kg, 150 lb ≈ 68 kg.
• Medical dosing is often calculated per kg of body weight even in the US — knowing your kg weight is useful for medication accuracy.
• Airline luggage limits typically use kg internationally (23 kg checked bag, 7-10 kg carry-on); US domestic flights often quote both.

Origin & history

The international avoirdupois pound was defined in 1959 as exactly 0.45359237 kg, harmonizing slightly different US and UK definitions. The kilogram, until 2019, was defined by a physical platinum-iridium cylinder; it's now defined by Planck's constant.

What is a pound?

One avoirdupois pound equals exactly 0.45359237 kilograms or 16 ounces. Body weight, groceries, and most everyday weight measurements in the US and informally in the UK.

What is a kilogram?

The kilogram is the SI base unit of mass, defined since 2019 by fixing the Planck constant. Body weight, groceries, freight, and most everyday weight measurements outside the US.

How to picture a lb

These anchors can be useful when sizing up a value.

• 1 lb — about the weight of a paperback book.
• 5 lb — about a bag of flour.
• 150 lb — roughly an average adult.

How to convert pound to kilogram

To convert a value from pound (lb) to kilogram (kg), apply the conversion factor shown in the formula above. The calculation is the same whether you do it by hand, in a spreadsheet, or with the live converter on this page.

Steps:

1. Take your input value in lb.
2. Apply the formula see formula above.
3. The result is your value in kg.

For repeated calculations, save the formula in a spreadsheet or use the live converter at the top of this page — it handles the math automatically and displays the result as you type.

Frequently asked questions

How do I convert lb to kg?

Apply the formula lb → kg shown above, or just type your value into the converter at the top of this page. The result updates instantly.

Which is bigger, lb or kg?

This depends on the conversion ratio in the formula. If the factor multiplied by your value gives a larger number, then kg is the smaller unit (so it takes more of them to express the same quantity). If the result is smaller, then kg is the larger unit.

When would I use lb versus kg?

Both units measure mass, so the choice depends on context. Pound is typically used for shipping, scientific measurement, cooking, and commerce; kilogram similarly. Most professional fields standardize on one or the other based on regional conventions or technical tradition.

How precise is this lb to kg conversion?

The conversion factor shown is the internationally defined exact value (or the best-published approximation if the relationship is irrational, like degrees-to-radians). The live converter on this page uses double-precision floating-point math, accurate to about 15 significant digits — far beyond any practical engineering need.

Is the conversion ratio exact, or an approximation?

Most unit conversions between SI metric units, and between SI and US customary units, have been formally defined as exact values since the 1959 international yard-pound agreement and subsequent SI redefinitions. Exceptions are unit pairs that involve irrational numbers (radians, e.g.) or empirical conversions (like food calories, which depend on temperature). When in doubt, consult the formula at the top of this page.

Related conversions

See also