Weight Converter: Pounds to Kilograms & All Unit Conversions

Why Weight Conversions Matter

Weight conversion is one of the most practical unit conversions in daily life. Whether you're reading a nutrition label in grams, checking a luggage allowance in kilograms, or following a recipe that calls for ounces, the ability to move between metric and imperial units quickly saves time and prevents mistakes.

The world runs on two parallel systems. The metric system — used by about 95% of the global population — measures weight in grams and kilograms. The imperial/US customary system uses ounces, pounds, and tons. The US is the only major economy that hasn't formally adopted the metric system for everyday use, which means conversions come up constantly for anyone working across borders.

Metric Weight Units

The metric system is based on powers of 10, making conversions straightforward once you know the base unit (gram).

The kilogram is the SI (International System of Units) base unit of mass — it's defined since 2019 by the Planck constant rather than a physical artifact. One milligram is the standard dosing unit for most medications: a 500 mg ibuprofen tablet weighs half a gram.

Imperial and US Customary Weight Units

The imperial system has a less uniform structure, with conversion factors that require memorization.

Note the difference between a US short ton (2,000 lbs) and a UK long ton (2,240 lbs). This 240-lb discrepancy matters in shipping contracts. The metric ton (tonne, 2,204.6 lbs) sits between them — always confirm which "ton" a document means before signing.

Key Conversion Reference Table

Bookmark this table. These are the conversions you'll use most often.

Weight vs Mass: The Technical Distinction

In everyday conversation, "weight" and "mass" are used interchangeably. Scientifically, they're different things.

Massis the amount of matter in an object. It's measured in kilograms (SI) or grams and doesn't change based on location. Your mass on Earth is the same as your mass on the Moon.

Weightis the gravitational force acting on that mass. It's technically measured in newtons (force = mass × acceleration). On the Moon, where gravity is about 1/6 of Earth's, you would weigh one-sixth as much — but your mass stays the same.

Why does this matter practically? In precision science and engineering, it matters a lot. A scale measures the gravitational force on an object and then back-calculates mass based on local gravity. Most commercial scales are calibrated for Earth's average gravity and technically read mass in kilograms. When you step on a bathroom scale and see "70 kg," the scale is reporting your mass — but we call it weight.

For everyday conversions: don't stress the distinction. Treat grams and kilograms as units of weight. The difference only matters in physics classrooms and spacecraft.

Top 5 Contexts Where Weight Conversions Are Essential

These are the situations where getting the conversion right actually has consequences.

1. Medical and pharmaceutical dosing.Medication doses are calculated as milligrams per kilogram of body weight (mg/kg). The FDA requires pediatric prescriptions to record patient weight in kilograms. A 2018 study in Pediatrics found that weight-unit errors (confusing lbs and kg) were the leading cause of 10-fold dosing errors in emergency departments. Converting a 44 lb child's weight to 20 kg correctly is the difference between a therapeutic dose and a dangerous one.

2. Airline baggage allowances.Major carriers publish limits in kilograms for international routes (usually 23 kg / 50 lbs for checked bags in economy) and in pounds for US domestic routes. A bag at 50.5 lbs will incur a heavy baggage fee of $75–$200 on most carriers. Knowing your bag weighs 23.5 kg before you reach the airport avoids surprise charges.

3. Cooking and baking across recipes. American recipes list ingredients in cups, ounces, and pounds; European and professional recipes list them in grams. A 200 g serving of flour is 7.05 oz or about 1.6 cups (sifted). Baking is particularly unforgiving: being off by 30 g on a bread recipe can mean the difference between a proper crumb and a dense brick.

4. International shipping and freight.Shipping carriers calculate cost by dimensional weight or actual weight in kilograms. A package that weighs 2.3 kg will be quoted differently than "approximately 5 lbs." Per IATA (International Air Transport Association) regulations, cargo manifests must list weight in kilograms. The US Postal Service caps domestic packages at 70 lbs (31.75 kg) for Priority Mail.

5. Olympic weightlifting and sports.Olympic weightlifting weight classes are defined in kilograms: 61 kg, 73 kg, 89 kg, 102 kg, and 102+ kg for men (as of 2024 Paris Olympics). An American athlete who weighs 160 lbs needs to know that converts to 72.57 kg — just under the 73 kg class. Missing a weight class cutoff by 0.5 kg can mean competing against heavier opponents.

Common Weight Benchmarks

When a number doesn't feel concrete, comparison helps. Use this table to anchor unfamiliar weights.

According to the CDC's 2021 National Health Statistics report, the average American man weighs 197.9 lbs (89.8 kg) and the average American woman weighs 170.8 lbs (77.5 kg) — both above global averages. These benchmarks are useful when reviewing weight-based medical guidelines published in kilograms.

Quick Mental Math Shortcuts

You won't always have a converter handy. These shortcuts work well enough for estimates.

Pounds to kilograms: Divide by 2, then subtract 10% of the result.
Example: 220 lbs → 110 → minus 11 = 99 kg (exact: 99.79 kg).

Kilograms to pounds: Multiply by 2, then add 10% of the result.
Example: 90 kg → 180 → plus 18 = 198 lbs (exact: 198.41 lbs).

Grams to ounces: Divide by 30 for a rough estimate (exact divisor is 28.35).
Example: 300 g → 300 ÷ 30 = 10 oz (exact: 10.58 oz).

Kilograms to stone: Multiply by 0.157, or roughly divide by 6.35.
Example: 76 kg ÷ 6.35 ≈ 12 stone (exact: 11.97 stone).

Weight in Aviation and Payload Limits

Commercial aviation is one of the most weight-sensitive industries. Aircraft are certified for a Maximum Takeoff Weight (MTOW) calculated in kilograms. A Boeing 737-800 has an MTOW of 79,016 kg (174,200 lbs). Every kilogram of payload — passengers, luggage, fuel, cargo — must fit within that limit.

Airlines use standardized passenger weights for load calculations. The FAA updated its standard passenger weight assumptions in 2023 to 190 lbs (86.2 kg) for summer travel including carry-on bags. If you have ever been on a small regional aircraft and been asked to step on a scale before boarding, this is why.

Weight Conversions in Everyday Cooking

Professional chefs and serious bakers weigh ingredients rather than measure by volume. Volume measurements like "a cup of flour" can vary by 20–30% depending on how the flour is packed. One cup of all-purpose flour weighs between 120 g and 150 g depending on sifting.

International recipe conversions you'll encounter:

• 100 g butter = 3.53 oz = roughly 7 tablespoons
• 500 g ground beef = 17.6 oz = just over 1 lb
• 1 kg potatoes = 2.2 lbs = about 6 medium potatoes
• 250 g flour = 8.82 oz = roughly 2 cups (unsifted)
• 30 g cheese = 1.06 oz = about one serving

For dedicated cooking conversions, see our Cooking Measurement Conversions Guide or the Cooking Measurement Converter tool.

BMI and Weight-for-Height Calculations

Body Mass Index (BMI) uses weight in kilograms and height in meters: BMI = kg / m². An American who weighs 185 lbs (83.91 kg) and stands 5'10" (1.778 m) has a BMI of 26.5, placing them in the "overweight" range (BMI 25–29.9) by CDC classification.

The conversion from lbs and inches to metric is where most BMI calculation errors happen. Always confirm the unit your calculator expects before entering values. Our BMI Calculator accepts both imperial and metric inputs and handles the conversion automatically.

Frequently Asked Questions

How do I convert pounds to kilograms?

To convert pounds to kilograms, multiply by 0.453592. So 150 lbs equals 150 × 0.453592 = 68.04 kg. The reverse conversion — kilograms to pounds — multiplies by 2.20462. A 70 kg person weighs approximately 154.3 lbs. For quick estimates, divide pounds by 2.2.

How many grams are in an ounce?

One ounce equals exactly 28.3495 grams. Sixteen ounces make one pound (453.592 grams). In cooking, this matters when a recipe calls for 100 g of flour but your scale reads ounces — that is 3.527 oz. Precious metals like gold are measured in troy ounces, which equal 31.1035 grams.

What is a stone in pounds?

A stone is a unit of weight used primarily in the UK and Ireland equal to 14 pounds or 6.35 kg. Body weight is still commonly expressed in stone in Britain — a person weighing 168 lbs is described as 12 stone. To convert stone to pounds, multiply by 14.

Is weight the same as mass?

Technically, no. Mass is the amount of matter in an object (measured in kilograms or grams) and does not change based on location. Weight is the force of gravity acting on that mass and varies by location — you weigh less on the Moon. In everyday use, however, the terms are used interchangeably.

How do I convert kg to lbs without a calculator?

A reliable mental shortcut: multiply kilograms by 2 and then add 10% of that result. For 80 kg: 80 × 2 = 160, plus 10% (16) = 176 lbs. The exact answer is 176.37 lbs, so the estimate is very close. For lbs to kg, divide by 2 and subtract 10% of the result.

Why do doctors use kilograms for medication dosing?

Medication doses are calculated as milligrams per kilogram of body weight (mg/kg), making metric units the clinical standard worldwide. Using kilograms avoids conversion errors: a 2.2x error from confusing pounds and kilograms can cause a dangerous overdose. The FDA requires weight-based dosing to be recorded in kilograms for all pediatric patients.

What is the maximum weight allowed in checked luggage?

Most major airlines set the checked bag limit at 50 lbs (23 kg) per bag for economy class on international routes. Bags over 50 lbs but under 70 lbs (32 kg) typically incur a heavy bag fee of $75–$200. Bags exceeding 70 lbs (32 kg) are often refused entirely. Domestic US limits are commonly 50 lbs as well.