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Weight Converter

Convert between kilograms, pounds, ounces, and grams instantly

Value

Kilograms (kg): 1.00

Pounds (lb): 2.20

Ounces (oz): 35.27

Grams (g): 1000

Reviewed by Dr. James Smith, Ph.D.

Physics Professor | Metrology Consultant

Last Updated: November 24, 2025

Understanding Weight and Mass

In everyday language, we use "weight" and "mass" interchangeably, but in science, they are distinct concepts. This calculator handles the conversion of mass units (like kilograms and pounds) which are commonly referred to as weight.

Mass vs. Weight: The Scientific Distinction

Mass is a measure of the amount of matter in an object. It is constant regardless of where you are in the universe. Your mass is the same on Earth, the Moon, or floating in space. The standard unit is the kilogram (kg).

Weight is the force of gravity acting on an object's mass. It depends on the gravitational field strength. On the Moon, where gravity is weaker, you would weigh about 1/6th of what you weigh on Earth, but your mass would remain exactly the same.

Weight (W) = Mass (m) × Gravity (g)
On Earth, g ≈ 9.8 m/s²

Common Units of Mass

Kilogram (kg): The base unit of mass in the International System of Units (SI). Originally defined by a physical prototype, now defined by the Planck constant.
Pound (lb): The primary unit of mass in the US Customary and British Imperial systems. Defined exactly as 0.45359237 kilograms.
Ounce (oz): 1/16th of a pound. Commonly used for food ingredients and precious metals (though precious metals use "troy ounces," which are different).
Gram (g): 1/1000th of a kilogram. Standard for small measurements in cooking and science.

💡 Expert Tips from Dr. Smith

The "Kilo" Confusion: In colloquial English, "kilo" always means kilogram. But in physics, "kilo" is just a prefix meaning 1000. A "kilometer" is 1000 meters. Always check the context.

Cooking Conversions: When a recipe calls for "8 oz of flour," that's a weight measurement (approx 227g). But "8 fl oz of milk" is a volume measurement (approx 237ml). Fluid ounces measure volume, regular ounces measure weight. They are not the same!

Gym Math: If you lift weights, you'll often see plates in lbs or kgs. A "20kg" plate is actually 44.1 lbs, but usually treated as 45 lbs in gym lore. A "45lb" plate is 20.4 kg. The slight difference adds up in powerlifting competitions.

⚠️ Common Mistakes to Avoid

Confusing Troy Ounces with Avoirdupois Ounces: Gold and silver are weighed in "Troy ounces" (approx 31.1g), which are heavier than standard "Avoirdupois ounces" (28.35g). If you buy gold thinking it's standard ounces, you might get less than you paid for!
Mixing up Tons: A "ton" can mean three things: Short Ton (US, 2000 lbs), Long Ton (UK, 2240 lbs), or Metric Tonne (1000 kg / 2204 lbs). Always clarify which ton is being used in shipping or trade.
Ignoring Container Weight (Tare): When weighing ingredients, always "tare" (zero out) the scale with the empty container on it first. Otherwise, you're including the bowl's weight in your measurement.

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Frequently Asked Questions

What is the difference between weight and mass?

Mass is the amount of matter in an object and remains constant everywhere (measured in kg). Weight is the force of gravity acting on that mass (measured in Newtons). However, in daily life, we use 'weight' to mean mass. A 70kg person has the same mass on the Moon but weighs only 1/6th as much. This converter handles 'mass' units (kg, lb) as they are commonly used for weight.

How many pounds are in a kilogram?

There are exactly 2.20462 pounds in one kilogram. To roughly convert kg to lbs in your head, double the kg and add 10%. For example, 50kg is about 110lbs (Actual: 110.23lbs). This approximation is very useful for gym weights or body weight.

Why do the US and UK use stones and pounds?

The 'stone' (14 lbs) is a traditional British unit still widely used in the UK and Ireland for body weight, though not in the US. The US uses pounds (lbs) exclusively. The metric system (kg) is standard almost everywhere else. 'Lb' comes from the Roman 'libra', meaning balance or scales.

How do I convert ounces to grams for cooking?

1 ounce (oz) equals approximately 28.35 grams. For cooking, it's often rounded to 28g or 30g depending on the precision needed. A standard 'cup' of flour weighs about 120g or 4.25 oz, but volume-to-weight conversion depends on the ingredient's density.

What is a metric ton vs. a US ton?

A Metric Tonne (t) is 1,000 kg (approx 2,204 lbs). A US Short Ton is 2,000 lbs (approx 907 kg). A British Long Ton is 2,240 lbs (approx 1,016 kg). Confusing these can lead to massive errors in shipping and logistics. Always specify which 'ton' you mean.

📚 Expert References & Further Reading

NIST - SI Units - Mass. https://www.nist.gov/
BIPM - Kilogram Definition. https://www.bipm.org/
Britannica - Avoirdupois Weight. https://www.britannica.com/