Weight conversion is one of those skills that quietly shows up everywhere: luggage at the airport, gym weight plates, baby weights, recipes from abroad, medication doses, shipping. The US is one of the few countries that still uses pounds and ounces; the rest of the world weighs in kilograms and grams. Here is everything you need to move confidently between the two.

The exact factor

1 pound = 0.45359237 kilograms (exactly, by international agreement since 1959).

1 kilogram = 2.20462262 pounds.

For most practical purposes, use 2.2046 or even 2.2.

Mental math shortcuts

Pounds to kilograms: divide by 2 and subtract 10%.

  • 150 lb ÷ 2 = 75. Minus 10% (7.5) = 67.5 kg. Exact: 68.0 kg. ✓
  • 200 lb ÷ 2 = 100. Minus 10% (10) = 90 kg. Exact: 90.7 kg. ✓
  • 50 lb ÷ 2 = 25. Minus 10% (2.5) = 22.5 kg. Exact: 22.7 kg. ✓

Kilograms to pounds: double and add 10%.

  • 70 kg × 2 = 140. Plus 10% (14) = 154 lb. Exact: 154.3 lb. ✓
  • 20 kg × 2 = 40. Plus 10% (4) = 44 lb. Exact: 44.1 lb. ✓

The trick is accurate within a percent or two — plenty for daily life.

Body weight benchmarks

  • 100 lb = 45.4 kg
  • 120 lb = 54.4 kg
  • 140 lb = 63.5 kg
  • 160 lb = 72.6 kg
  • 180 lb = 81.6 kg
  • 200 lb = 90.7 kg
  • 250 lb = 113.4 kg

Luggage limits

Most international airlines use kilograms:

  • Carry-on: 7–10 kg (15.4–22 lb)
  • Checked economy: 23 kg (50.7 lb)
  • Checked business: 32 kg (70.5 lb)
  • Excess fee typically triggers over the listed weight

The 23 kg limit is why US travelers often hear "50 pounds" quoted — it's the rounded imperial version of the 23 kg standard.

Gym plates

US gym plates come in pounds: 2.5, 5, 10, 25, 35, 45.

International (and Olympic) plates come in kilograms: 0.5, 1.25, 2.5, 5, 10, 15, 20, 25.

A "standard barbell" is 45 lb (US) or 20 kg (international) — they differ slightly (45 lb = 20.4 kg).

Common matches:

  • 45 lb plate ≈ 20 kg plate (off by ~2%)
  • 25 lb plate ≈ 11.3 kg (no direct match in the 10 kg system; closest is 10 kg)
  • 10 lb plate ≈ 4.5 kg

This matters for international competitions where lifts are recorded in kg.

Baby weights

Newborn weights:

  • 5 lb = 2.27 kg
  • 6 lb = 2.72 kg
  • 7 lb = 3.18 kg (average US birth weight)
  • 8 lb = 3.63 kg
  • 9 lb = 4.08 kg
  • 10 lb = 4.54 kg

Hospitals outside the US almost always record in grams (3,500 g = 3.5 kg) or kg directly. A 3,500 g baby is about 7 lb 11 oz.

Cooking and recipes

Most international baking recipes weigh ingredients in grams. US baking often uses cups. Precision baking (breads, pastries) benefits enormously from metric weights — a "cup of flour" can vary by 20% depending on how it is packed.

Common flour conversions:

  • 1 cup all-purpose flour = 120 g
  • 1 cup bread flour = 130 g
  • 1 cup sugar = 200 g
  • 1 cup butter = 227 g = 1/2 lb

A pound is 16 oz = 453.6 g. Half a pound is 227 g — exactly one stick of butter in US stores.

Medical weights

Many medications dose by milligram per kilogram. A drug labeled "5 mg/kg" given to a 180 lb (82 kg) adult delivers 410 mg. US pediatricians often convert patient weight to kg before calculating doses — this is standard practice worldwide.

Shipping

Parcel rates commonly use pounds in the US but kilograms internationally. A "2 lb package" internationally is billed as "1 kg" (typically rounded up). International couriers like FedEx and DHL display both.

Grams, ounces, stones

  • 1 oz = 28.35 g
  • 1 lb = 16 oz = 453.6 g
  • 1 stone = 14 lb = 6.35 kg (UK-specific; rarely used in the US)
  • 1 kg = 2.205 lb = 35.27 oz

Use the tool

Our weight converter handles pounds, kilograms, grams, ounces, stones, and milligrams in any combination. Enter one value, get them all. Perfect for packing suitcases, reading international recipes, tracking fitness progress, or shipping internationally. Weight conversion is a ten-second task — once you hand it to a calculator.