Weight Converter

The Weight Converter translates mass values between the metric system (milligram, gram, kilogram, tonne) and the imperial system (ounce, pound, stone, US ton, UK long ton) in one integrated interface. Everyday life throws this conversion at you constantly: a bag of flour calls for 500 g in a recipe but your American kitchen scale reads ounces, a box label shows 2.5 kg but your shipping form wants pounds, a gym routine demands 225 lb on the bar but the plates are labeled in kilograms, a pediatrician records baby weight in ounces while the family chat expects kilograms.

This tool handles nine common units at once and includes specialty units for pharmacy (grain, troy ounce) and gemstones (carat). Type a value in any field and every other field updates instantly. Arithmetic uses the exact international definition (1 lb = 0.45359237 kg exactly), which means round-trip conversions never drift — type 10 kg, read 22.046 lb, type 22.046 lb back, and you get 10 kg (at standard display precision). Compound inputs like 11 stone 7 pounds are parsed automatically to match how British body weight is often spoken, and quick conversions for common cooking and gym values are one keystroke away.

The international avoirdupois pound has been defined since 1959 as exactly 0.45359237 kilograms. This is a rational, exact relationship, so the mass-to-pound conversion is precise to arbitrary decimal places within floating-point limits. Every imperial weight unit derives from the pound: 1 ounce = 1/16 lb = 28.349523125 g exactly, 1 stone = 14 lb = 6.35029318 kg exactly, 1 US ton = 2000 lb = 907.18474 kg exactly, 1 UK long ton = 2240 lb = 1016.0469088 kg exactly, 1 grain = 1/7000 lb = 0.06479891 g exactly.

Metric units follow SI prefix math with exact decimal factors: 1 tonne = 1000 kg, 1 kg = 1000 g, 1 g = 1000 mg, 1 mg = 1000 μg. No rounding or precision loss across the chain.

Specialty units have their own international definitions: 1 troy ounce (precious metals) = 31.1034768 g exactly, 1 carat (gemstones) = 200 mg = 0.2 g exactly, 1 pennyweight = 1/20 troy ounce. The troy system is distinct from avoirdupois — mixing them up is the classic rookie mistake with gold prices, where a troy ounce of gold weighs more than an avoirdupois ounce.

Mass versus weight: strictly, mass (measured in kg) is the amount of matter, while weight (measured in newtons) is the force of gravity on that mass. On Earth\u2019s surface the two are proportional so the distinction is rarely important in daily life. This converter handles mass units throughout — the label \"weight\" is used informally because that is what people search for, but the underlying quantity is mass everywhere except in physics contexts that explicitly require force units.

Compared to typing '5 lb in kg' into Google, this tool shows every unit at once plus specialty units like troy ounce and carat. For a single casual conversion the search box is faster; for any real work (kitchen, gym, shipping) the side-by-side view wins.

Compared to dedicated fitness or cooking apps, the browser version works on any device with no install and no login. Specialty apps sometimes hide units behind menus or add unnecessary friction; a flat all-at-once view is quicker for most conversions.

Compared to scientific calculators with unit support, this tool covers everyday mass conversion without the learning curve. For dimensional analysis and unit-aware coding, use a proper library like Python Pint or JavaScript convert-units. For reading a recipe or verifying a shipping weight, this tool is the right level of abstraction.