Weight / Mass Converter

Weight Conversion: Mass vs Force, the Jin Family, and the Troy Ounce Trap

A conceptual fix first: mass versus weight

Strictly, mass is measured in kilograms (kg) and is the amount of matter, constant regardless of location. Weight is the gravitational force on that mass, measured in newtons (N), and it changes with local gravity — the same object weighs about 0.5% less at the equator than at the pole.

When people say "I weigh 70 kg" they mean mass. The distinction becomes a real problem in aerospace, precision measurement, and buoyancy scenarios; for everyday conversion you can treat it as mass.

The kilogram is the only SI base unit carrying a prefix, a historical quirk (the gram was originally the base, later swapped for the kilogram). The rule that follows: multiply prefixes attach to the gram — write milligram (mg), never microkilogram.

The Chinese "jin" is not one unit

This is where real transactions lose money: the same word "one jin" is 500 g on the mainland, 600 g in Taiwan, and about 605 g in Hong Kong — a gap of up to 20%. The subordinate unit "liang" also shifts (in the old 16-liang-to-a-jin system, the liang differs by region). At a market, pharmacy, or reading an old scale, always confirm which jin you are dealing with.

Extra wrinkle: mainland China modernized to "1 jin = 10 liang = 500 g" in 1959, but Taiwan and Hong Kong still use "1 jin = 16 liang". That makes the liang conversion entirely different between them.

Pound, ounce, and the troy system

The third row is the important one: gold, silver, and platinum are always priced in troy ounces, never avoirdupois ounces. They differ by about 9.7% (31.10 vs 28.35 g). Converting a gold price with the avoirdupois ounce understates it by nearly 10% — a conversion error that costs real money.

A related trap seen online: "ounce to RMB" calculators use the troy ounce, applying price (USD/troy oz) × rate / 31.1035 to get yuan per gram. Using 28.35 would come out visibly too low.

Three different tons

When English text says "ton" without context, the difference is close to 10% — confirm the country of origin. In shipping contracts and bulk trade this distinction is a material clause.

Recording and conversion caveats

• Net versus gross. In freight, customs, and recipes these differ (gross includes packaging). Check which the header states before costing from gross weight.
• Precision and rounding point. 1 pound = 453.59237 g; rounding to 454 g loses about 0.09%. Across a batch (say 1000 items) that compounds into a visible difference. Settle trades on the exact value, round only at final display.
• Density is not a weight conversion. "How many kg in a liter" depends on the substance's density — water is near 1 kg/L but oil, alcohol, and honey differ. That needs a density parameter, not a unit swap.
• Fineness affects precious-metal mass. A troy ounce weighs the alloy; the quote is for pure content, with a fineness step in between. A pure unit conversion ignores that layer.

The tool covers kilogram, gram, milligram, ton, quintal, pound, ounce, troy ounce, stone, market jin, Taiwan jin, and Sima jin — all converted locally in the browser.