Weight & Mass Converter
Convert between kilograms, pounds, ounces, grams and more.
Where "Weight" Conversions Go Wrong — and Why It Matters
Most conversion errors with mass and weight come from two overlooked distinctions: the metric tonne vs. the US ton vs. the UK long ton, and the loose everyday use of "weight" to mean "mass." Let's unpack both.
In physics, mass measures how much matter an object contains (kilograms, grams, pounds-mass), while weight is the gravitational force acting on that mass (newtons). A 70 kg person has the same mass on the Moon as on Earth, but weighs only about 114 N on the Moon versus 686 N on Earth. For everyday shipping, cooking, and commerce this distinction is irrelevant — but for engineering and aerospace calculations, confusing the two collapses rockets.
The Three "Tons" Problem
The word "ton" alone is dangerously ambiguous. Three distinct units share the name:
- Metric tonne (t): 1,000 kg = 2,204.62 lb. The SI standard and the globally dominant usage in trade.
- Short ton (US ton): 2,000 lb = 907.185 kg. Standard in US commercial and agricultural contexts.
- Long ton (Imperial ton): 2,240 lb = 1,016.05 kg. Historical UK usage; still seen in shipping and naval contexts.
A cargo listed as "100 tons" without specification differs by 10,860 kg between metric and short ton interpretations. Always confirm which ton applies in any international shipment or contract.
Mass in Cooking vs. Science
Culinary recipes from the US often specify volume (cups, tablespoons) where professional baking and all scientific protocols require mass. Converting between them requires knowing the ingredient's density — water is 1 g/mL, bread flour is roughly 0.53 g/mL, and honey is about 1.42 g/mL. This tool handles mass-to-mass conversion only; for volume-to-mass conversions you need the density of your specific ingredient.
Precision Considerations for Pharmaceuticals and Chemistry
At the milligram and microgram scale, measurement precision becomes critical. 1 mg = 0.001 g = 0.0000353 oz. A 5% rounding error in a 200 mg dose represents 10 mg — a clinically significant margin for many drugs. For pharmaceutical calculations, always work in milligrams throughout and convert only for the final patient-facing label. Never use pound-to-milligram conversions with fewer than six significant figures.
How to Use This Tool
- Enter a numeric value in any unit field.
- All other unit fields update instantly with full precision.
- All major mass units are included: milligram, gram, kilogram, metric tonne, ounce, pound, stone, short ton, and long ton.
⇄ FAQ
01 What is the difference between a metric tonne and a US ton? +
A metric tonne is 1,000 kg (2,204.62 lb). A US short ton is 2,000 lb (907.19 kg). They differ by about 10%. Always confirm which is meant in contracts, shipping documents, and agricultural records.
02 How do I convert kilograms to pounds precisely? +
1 kg = 2.20462262185 lb (to 11 significant figures). For most purposes, 2.20462 is sufficient. Multiply your kg value by this factor; do not use the approximation 2.2 for anything requiring more than 2 significant figures in the result.
03 Why does my kitchen scale use grams instead of ounces for baking? +
Grams offer finer resolution for small quantities and eliminate the density problem. 100 g of flour is always 100 g regardless of how tightly it was packed, whereas a "cup" of flour can vary by 20–30% depending on scooping technique.
04 Is weight the same as mass? +
Physically, no. Mass is an intrinsic property measured in kg; weight is a force (mass × gravitational acceleration) measured in newtons. Colloquially and commercially they are used interchangeably on Earth, where gravitational acceleration varies less than 0.5% across locations.
