Weight Conversion Guide: Kilograms, Pounds, Ounces, and More

12 min read•June 1, 2026•Reviewed: June 1, 2026

✓Reviewed by Apex Conversion Editorial Team · Last reviewed June 1, 2026

Weight and mass conversion is one of the most frequent measurement tasks in everyday life. You encounter it when reading nutrition labels, shipping packages, following a recipe from another country, checking baggage at the airport, or monitoring health metrics on a global fitness app. The challenge is that two completely different systems — metric and imperial — are both in active daily use worldwide.

This guide covers kilograms, grams, milligrams, pounds, ounces, stones, and metric tons with exact formulas, practical memory anchors, and worked examples. Whether you are a nurse calculating medication dosages, a chef adapting a recipe, or a traveler checking a luggage limit, the information here applies directly to your task.

What the Units Mean

The kilogram (kg) is the SI base unit of mass. In 2019 it was redefined in terms of the Planck constant — making it one of the most precisely defined quantities in science. Derived metric units: milligram (mg) = 0.000001 kg, gram (g) = 0.001 kg, metric ton (t) = 1,000 kg.

The pound (lb) is the primary mass unit in the US customary and UK imperial systems. 1 lb = 0.45359237 kg exactly (by international agreement since 1959). Derived units: ounce (oz) — 16 oz = 1 lb. Stone (st) — 14 lb = 1 stone, used informally in the UK and Ireland for body weight. Short ton (US ton) = 2,000 lb ≈ 907.185 kg. Long ton (UK) = 2,240 lb ≈ 1,016 kg.

Common Units and Typical Uses

Milligrams (mg): pharmaceutical dosages, supplement amounts, micronutrient content on food labels. Grams (g): food ingredients, postal weights, precious metals (gold priced per gram), jewelry. Kilograms (kg): body weight in most countries, produce, shipping weights, luggage limits, sports equipment ratings.

Pounds (lb): US body weight, US food packaging, US postal weights, US luggage limits. Ounces (oz): US food serving sizes, precious metal trading, small package weights. Stone (st): UK/Ireland informal body weight. Metric ton (t): international freight, large commodity shipments, vehicle curb weights.

Key Conversion Formulas

━━━ POUNDS ↔ KILOGRAMS ━━━
  kg  = lb  × 0.453592     lb  = kg  × 2.20462
  Quick estimate: kg × 2.2 ≈ lb (within 0.21%)
  Example: 150 lb × 0.453592 = 68.04 kg

━━━ OUNCES ↔ GRAMS ━━━
  g   = oz  × 28.3495      oz  = g   × 0.035274
  Quick estimate: g ÷ 28 ≈ oz (within 0.18%)
  Example: 16 oz × 28.3495 = 453.59 g (= 1 lb)

━━━ STONE ↔ POUNDS ↔ KILOGRAMS ━━━
  lb  = st  × 14 (exact)   kg  = st  × 6.35029
  Example: 11 st × 14 = 154 lb × 0.453592 = 69.85 kg

━━━ METRIC ━━━
  g   = kg  × 1,000  (exact)    mg  = g × 1,000  (exact)
  t   = kg  ÷ 1,000  (exact)    1 t = 2,204.62 lb

Real-World Examples

Airline baggage: international check-in limits are typically 23 kg. A US traveler accustomed to 50 lb limits: 23 kg × 2.20462 = 50.71 lb ≈ 50 lb. Carry-on limits are often 7–10 kg (15.4–22 lb). Overweight charges trigger above 23 kg; calculating your bag weight before the airport avoids surprises.

Cooking and baking: a US recipe calling for 2 lb of flour: 2 × 453.592 = 907 g ≈ 900 g (close enough for baking). A European recipe calling for 500 g of butter: 500 ÷ 453.592 = 1.10 lb ≈ 1 lb 1.7 oz. One US stick of butter is 113.4 g (4 oz = 0.25 lb).

Body weight: a person weighing 70 kg: 70 × 2.20462 = 154.3 lb = 11 st 0.3 lb ≈ 11 stone in UK conversation. A child weighing 55 lb: 55 × 0.453592 = 24.95 kg ≈ 25 kg. Weight loss apps increasingly show both kg and lb simultaneously.

Common Mistakes to Avoid

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Using 2.2 as the lbs-to-kg factor: the exact factor is 2.20462. For body weight tracking and medical use, use 2.20462 to avoid compounding errors.
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Confusing weight ounces (oz) and fluid ounces (fl oz): oz measures mass; fl oz measures volume. 1 fl oz of water weighs approximately 1.04 oz but other liquids differ.
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Mixing short tons (US), long tons (UK), and metric tons: US short ton = 2,000 lb = 907 kg. UK long ton = 2,240 lb = 1,016 kg. Metric ton = 1,000 kg = 2,204.62 lb. For international shipping, always confirm which ton is meant.
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Forgetting that stone is 14 pounds (not 10 or 12): 1 stone = exactly 14 lb. 11 stone 7 = (11 × 14) + 7 = 161 lb = 73.03 kg.
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Using troy ounces for food or avoirdupois ounces for precious metals: 1 troy oz = 31.1035 g vs. 1 avoirdupois oz = 28.3495 g — about 10% heavier. Gold and silver are always priced in troy ounces.

Frequently Asked Questions

How many pounds is 1 kilogram?

1 kilogram = 2.20462 pounds exactly. The exact definition: 1 lb = 0.45359237 kg, so 1 kg = 1 ÷ 0.45359237 = 2.20462 lb. A quick approximation: multiply kg by 2.2 — accurate within 0.21%.

How many kilograms is 100 pounds?

100 lb × 0.453592 = 45.36 kg. This is a useful anchor: 100 lb ≈ 45 kg. 200 lb ≈ 90 kg. 50 lb ≈ 22.5 kg.

How many grams is 1 ounce?

1 avoirdupois ounce = 28.3495 grams. A quick approximation: 1 oz ≈ 28 g. This is different from a troy ounce (used for precious metals), which is 31.1035 g.

How many pounds is 1 stone?

1 stone = 14 pounds exactly. To convert stone to kg: multiply by 6.35029. Example: 10 stone = 140 lb = 63.5 kg.

What is the weight limit for airline carry-on in kg?

Most international carriers allow 7–10 kg (15.4–22 lb) for carry-on bags. US domestic carriers often use linear inches instead of weight. Always check the specific airline: low-cost carriers like Ryanair and EasyJet have stricter limits (typically 10 kg / 22 lb).

How do I convert mg to g?

Divide milligrams by 1,000 to get grams. 500 mg = 0.5 g. 1,000 mg = 1 g. This conversion matters for supplement doses: a vitamin tablet labeled 250 mg contains 0.25 g of active ingredient.

How many pounds is a metric ton?

1 metric ton = 1,000 kg × 2.20462 lb/kg = 2,204.62 lb ≈ 2,205 lb. A metric ton is about 10% heavier than a US short ton (2,000 lb).

How do I weigh myself accurately in kg vs. lb?

Modern bathroom scales display in both. For conversion: body weight in lb ÷ 2.205 = kg. Body weight in kg × 2.205 = lb. Weigh yourself at the same time each day (morning, after bathroom, before eating) for consistent results regardless of unit.

How many ounces is 200 grams?

200 g ÷ 28.3495 = 7.05 oz. A 200-gram portion of chicken breast is just over 7 oz. Many US food packages are labeled in both oz and g for this reason.

What is 1 pound in grams?

1 lb = 16 oz × 28.3495 g/oz = 453.59 g ≈ 454 g. Equivalently, 1 lb = 0.453592 kg × 1,000 g/kg = 453.592 g. This is one of the most important cooking conversions for adapting US recipes.

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