How do I convert pounds to kilograms?

Divide the weight in pounds by 2.205 to get kilograms. For a quick estimate, divide by 2.2. So 150 pounds ÷ 2.2 = approximately 68 kg.

Why does the US use pounds instead of kilograms?

The US inherited the imperial system from Britain and never officially switched. Congress authorized metric use in 1866 but never mandated it. Cultural inertia and conversion costs have kept pounds, miles, and Fahrenheit in everyday use.

What weighs exactly 1 kilogram?

A liter of water at 4°C weighs almost exactly 1 kilogram. Common objects close to 1 kg include a standard pineapple, a hardcover dictionary, or two cans of soup.

Is a stone still used as a unit of weight?

Yes, in the UK and Ireland, body weight is often expressed in stones (1 stone = 14 pounds = 6.35 kg). A 154-pound person weighs 11 stone. It's rarely used outside the British Isles.

Pounds to Kilograms and Back — The Complete Weight Conversion Guide

You’re at the gym in another country. The dumbbell rack shows 20 kg. Is that heavy or light? Or you’re ordering something online from Europe, and the shipping calculator wants your package weight in kilograms. If you grew up with pounds, these conversions don’t come naturally.

Let’s fix that with a clear, practical guide to weight conversions.

The Core Formula

The key number to remember is 2.205.

To convert pounds to kilograms, divide by 2.205. So 170 pounds ÷ 2.205 = 77.1 kg.

To convert kilograms to pounds, multiply by 2.205. So 80 kg × 2.205 = 176.4 pounds.

For quick mental math, just use 2.2. It’s close enough for most purposes and much easier to calculate in your head.

Quick Reference Chart

Here are the most common conversions people search for:

100 pounds is about 45.4 kg. 120 pounds is 54.4 kg. 140 pounds is 63.5 kg. 150 pounds is 68 kg. 160 pounds is 72.6 kg. 180 pounds is 81.6 kg. 200 pounds is 90.7 kg.

Going the other direction: 50 kg is 110.2 pounds. 60 kg is 132.3 pounds. 70 kg is 154.3 pounds. 75 kg is 165.3 pounds. 80 kg is 176.4 pounds. 90 kg is 198.4 pounds. 100 kg is 220.5 pounds.

Smaller Units: Ounces and Grams

For smaller weights — cooking, postage, jewelry — you’ll need ounces and grams.

1 ounce = 28.35 grams. 1 pound = 16 ounces = 453.6 grams. 1 kilogram = 1,000 grams = 35.27 ounces.

A practical shortcut: 1 ounce is roughly 28 grams. So that 8-ounce steak is about 227 grams, and a 100-gram chocolate bar is about 3.5 ounces.

Why Two Systems Exist

The metric system was created in France in 1795, designed to be logical and consistent — everything based on factors of 10. The imperial system evolved organically from Roman, Anglo-Saxon, and other historical measurements.

Today, only three countries haven’t officially adopted the metric system: the United States, Myanmar, and Liberia. However, even in the US, metric is standard in science, medicine, the military, and international trade.

The ironic part? The US pound is officially defined in terms of the kilogram. One pound is legally defined as exactly 0.45359237 kilograms.

When Precision Matters

For cooking at home, rounding to the nearest gram is fine. But certain fields demand precision. Pharmaceuticals measure in milligrams. Gemstones use carats (1 carat = 0.2 grams). Precious metals use troy ounces (1 troy ounce = 31.1 grams, different from the standard 28.35-gram ounce).

Convert Instantly

Skip the math and use our free Weight Converter for instant, accurate conversions between pounds, kilograms, ounces, grams, and more.