Weight Conversion: Grams, Pounds, Stone, and the Ton Trap

Weight is the conversion people do most often without thinking: a kitchen scale reads grams, the gym loads plates in pounds, the airline wants kilograms, and a British medical form asks for stone. The Weight Converter answers all of those from one input, and the reason it can is that every unit on its list is defined by one fixed number of grams.

Everything pivots through grams

The converter uses the pass-through-one-base method every unit tool relies on: multiply the input by its factor to reach grams, then divide by each target unit's factor. The whole tool is therefore just one table of definitions:

1 mg    = 0.001 g
1 g     = 1 g            (the pivot)
1 kg    = 1,000 g
1 oz    = 28.3495 g
1 lb    = 453.592 g
1 stone = 6,350.29 g     (14 lb)
1 ton   = 1,000,000 g    (metric tonne)

Enter 150 lb and the tool computes 150 × 453.592 = 68,038.8 g once, then reads off 68.0388 kg, 2,400.9 oz, 10.714 stone, and every other unit from that same number. Nothing is ever converted unit-to-unit directly, which is what keeps a seven-unit table internally consistent.

The factors are definitions, rounded for display

Since the 1959 international agreement the pound has been defined as exactly 453.59237 grams, which fixes the ounce at 28.349523125 g and the stone at 6,350.29318 g. The converter stores slightly rounded factors — 453.592, 28.3495, 6,350.29 — and rounds results to six decimal places. The drift is on the order of one part per million: invisible for groceries, luggage, and body weight, worth remembering for calibration-grade lab work. This pattern of exact definitions behind rounded factors runs through the whole customary system, a history told in Why Two Measurement Systems.

The ton trap: three units, one name

The converter's "ton" is the metric tonne: exactly 1,000 kg. Two other tons share the word, and they are not close:

metric tonne   = 1,000 kg   = 2,204.62 lb
US short ton   = 2,000 lb   =   907.185 kg
UK long ton    = 2,240 lb   = 1,016.05 kg

Shipping quotes, scrap metal, and aggregate pricing all hinge on which ton is meant — the short and long ton differ by 11% on their own. When a ton figure crosses a border or an industry, convert it to kilograms first and compare there; a converter that only knows metric tonnes will not silently absorb the difference for you.

Stone: the unit that never travels alone

Stone survives in daily use almost entirely as British body weight, and it is spoken as a mixed number: "11 stone 4" means 11 stone plus 4 pounds, not 11.4 stone. To convert, multiply the stone count by 14, add the pounds, then apply the pound factor: 11 st 4 lb = 158 lb = 71.67 kg. Going the other way, divide the kilograms by 6.35029 and take the whole number as stones; multiply the fractional remainder by 14 to recover the leftover pounds.

Metric steps are just powers of ten

Half the table is trivial because milligrams, grams, and kilograms differ by clean factors of 1,000 — that is the metric system doing its job. The only factors that need memorizing are the customary ones, and two shortcuts cover most daily life: 1 kg is about 2.2 lb, and 1 oz is about 28 g. One caution belongs to the kitchen: recipes written in grams measure mass, while cup measures hold volume, and the two are not interchangeable for flour, sugar, or butter. The Cooking Converter handles the volume side; a weight converter handles the scale side, and confusing them is the most common baking measurement error.

Try it yourself

Type any weight into the Weight Converter and read every unit at once — try 70 kg for a typical adult, then check the stone reading against the stone-plus-pounds method above. If the number came from a recipe, cross-check volumes with the Cooking Converter, and when a parcel's dimensions need the same treatment as its mass, the Length Converter completes the set.