⚖️ Weight Converter

Weight and Mass Conversion Guide

Weight and mass conversions are among the most frequently needed unit conversions in everyday life — cooking, fitness, shipping, medicine, science, and international commerce all use different weight systems. The two primary systems are the metric/SI system (kilograms, grams) used by most of the world, and the imperial/US customary system (pounds, ounces) used primarily in the United States and United Kingdom.

A technical note: weight and mass are different concepts in physics. Mass is the amount of matter in an object (measured in kilograms). Weight is the gravitational force on that mass (measured in Newtons). However, in everyday contexts — bathroom scales, cooking, shipping — "weight" and "mass" are used interchangeably, and this converter treats them equivalently for practical purposes.

Complete Unit Reference

• Metric ton (tonne): 1,000 kg = 2,204.62 lbs — used in international commerce and shipping
• Kilogram (kg): The SI base unit of mass. 1 kg = 1,000 grams = 2.20462 lbs
• Gram (g): 0.001 kg = 0.035274 ounces — cooking and pharmaceutical measurements
• Milligram (mg): 0.001 gram — medication dosages and micronutrient quantities
• Pound (lb): 453.592 grams = 16 ounces — the primary unit of everyday weight in the U.S.
• Ounce (oz): 28.3495 grams — cooking measurements, product packaging, precious metals (troy ounce = 31.1g)
• Stone (st): 14 pounds = 6.35 kg — body weight unit in the UK and Ireland
• Short ton (US ton): 2,000 lbs = 907.185 kg — U.S. commercial and industrial use
• Long ton (Imperial ton): 2,240 lbs = 1,016.05 kg — UK commercial use

Essential Quick-Reference Conversions

• 1 kg = 2.205 lbs (memorize as "roughly 2.2 lbs per kg")
• 1 lb = 0.4536 kg (memorize as "roughly 450 grams per pound")
• 1 oz = 28.35 g (roughly 28 grams per ounce)
• 1 stone = 14 lbs = 6.35 kg
• 100 lbs = 45.36 kg
• 1 metric ton = 1.102 US tons = 0.984 long tons

Practical Applications by Context

• Cooking and baking: U.S. recipes use cups, ounces, and pounds. European recipes typically use grams and kilograms. 1 cup of all-purpose flour ≈ 120–130g (it varies by how densely packed). Kitchen scales in grams are more precise than volume measurements for baking.
• Body weight: Americans weigh themselves in pounds; most of the world uses kilograms; UK residents often use stones. To convert your weight between systems: divide pounds by 2.205 to get kg; divide kg by 6.35 to get stones.
• Fitness and exercise: Dumbbells and barbells in the U.S. are labeled in pounds; most international equipment uses kg. A 45 lb plate ≈ 20.4 kg; a 25 lb plate ≈ 11.3 kg.
• Postal and shipping: USPS rates in the U.S. are by pounds and ounces. International shipping uses kilograms. Most carriers convert automatically, but understanding the relationship helps when estimating shipping costs.
• Precious metals: Gold and silver are measured in troy ounces (31.1g each), NOT regular (avoirdupois) ounces (28.35g). A troy pound = 12 troy ounces = 373.24g, significantly different from a regular pound (453.59g).

Mental Estimation Shortcuts

• Converting kg to lbs: Multiply by 2 and add 10% of the original. 70 kg → 140 + 7 = 147 lbs (actual: 154 lbs — not perfect, but quick). Better: multiply by 2.2. 70 × 2.2 = 154 lbs.
• Converting lbs to kg: Divide by 2 and subtract 10% of the result. 150 lbs → 75 − 7.5 = 67.5 kg (actual: 68.04 kg). Close enough for most purposes.
• Kitchen ounces to grams: Multiply by 28. 4 oz × 28 = 112g (actual: 113.4g).

Frequently Asked Questions

What's the difference between an ounce (oz) and a fluid ounce (fl oz)? A regular ounce measures mass/weight (28.35 grams). A fluid ounce measures volume (29.57 mL in the US). They're coincidentally similar in size for water (1 fl oz of water weighs approximately 1.04 oz) but diverge significantly for denser substances. Never use them interchangeably in recipes.

What is a "metric ton" vs a regular ton? A metric ton (or tonne) is exactly 1,000 kg (2,204.6 lbs). A US short ton is 2,000 lbs (907.2 kg). A UK long ton is 2,240 lbs (1,016 kg). International shipping and commodities markets use metric tons. U.S. domestic freight often uses short tons. Always clarify which "ton" is meant in commercial contracts.

Why is the troy ounce different from the regular ounce? The troy system (troy pound, troy ounce) derives from medieval Troyes, France, a major trading city. It survived specifically for precious metals (gold, silver, platinum) and gemstones while the avoirdupois system became standard for everyday goods. A troy ounce of gold (31.1g) is 10% heavier than a regular ounce (28.35g) — a significant difference in pricing.