Weight is an object's gravity force measurement, calculated by multiplying its mass by the local gravitational acceleration (often Earth's 9.8 m/s²) for a result in Newtons: weight = mass x gravity;
While often used interchangeably with mass in daily life, mass is constant, but weight changes depending on location (e.g., one weight less on the Moon).
Mass and weight contrast: Mass is how much space one occupies, weight is how much its gravity is
Newton (N)
Gram (g): 1/1000th of a kilogram
Milligram (mg): 1/1000th of a gram (tiny amounts)
Tonne (t): 1,000 kilograms (large weights)
Other Metric: Hectogram (hg), Decagram (dag), Centigram (cg)
Ounce (oz): Smallest common unit (~28g)
Pound (lb): 16 oz (common for body weight, groceries)
Stone (st): Used in UK (14 lbs)
Ton (T): 2,000 lb (US) or 2,240 lb (long ton in UK) for very heavy
Some units of mass and weight are used in specific industries, high-precision science, or historical commerce IO daily.
Material and jewerly
Troy Ounce (oz t): The global standard for pricing gold, silver, and platinum. It is heavier than a standard ounce, weighing 31.103 grams.
Metric Carat (ct): Used exclusively for gemstones and pearls; one carat is exactly 200 milligrams.
Pennyweight (dwt): Used in North American jewelry making; it equals 1.555 grams or 1/20th of a troy ounce.
Grain (gr): One of the smallest units (~64.8 mg), used today for bullets and gunpowder in ballistics and for pearls.
Momme (mm): A traditional Japanese unit (3.75g) still used internationally as the standard for weighing pearls.
Scientific and physics units
In physics, "weight" is defined as a force (mass × gravity), leading to specialized units that differ from standard mass.
Newton (N): official SI weight unit. On Earth, a 1 kg mass "weighs" ~9.8 N.
Dalton (Da) / Atomic Mass Unit (u): Used to measure mass at the molecular level, roughly equivalent to the mass of one proton or neutron.
Slug: A unit of mass in the US customary system defined as the mass that accelerates at 1 ft/s2 when 1 pound-force is applied (~14.59 kg).
Solar Mass (M☉): Used in astronomy to measure stars and galaxies; it equals the mass of our Sun (~2x1030 kg).
Regional and historical trade units
These remain in use for specific commodities or in local markets.
Tola: A traditional unit in South Asia (approx. 11.66g) used for gold.
Tael: Used in East Asia for gold and herbal medicines; its value varies by region (e.g., 37.5g in Hong Kong).
Stone (st): A British unit for human body weight equal to 14 pounds.
Apothecaries' units: Includes scruples and drams; formerly the standard for pharmacy, these have been almost entirely replaced by metric (milligrams) in 2026.
Derived units are measurements of complex physical quantities (like speed, force, energy, pressure) made by combining the 7 SI base units (meter, kilogram, second, ampere, kelvin, mole, candela) through multiplication or division.
All weight units are derived from kg·m/s², which can be scaled via grams, tons, cm, km, ft, lbm, etc., which gives all the different derived units you see (dyne, kgf, lbf, etc.).
Derived weight units:
1 kg⋅m/s2 = 1 N
Note: We often misuse "weight" with mass when we really mean “mass.” E.g., “I weigh 60 kilograms” is actually wrong, as kilograms measure mass, not force. The correct physics statement is “My mass is 60 kg, so my weight is 60 × 9.8 ≈ 588 N.”
weight = mass x gravity and mass = weight ÷ gravity;
Newtonweight (N) → Kilogrammass (kg): 1 N = 1 ÷ 9.8 = 0.102 kg
Newtonweight (N) ← Kilogrammass (kg): 1 kg = 1 x 9.8 = 1.98 N
Newtonweight (N) → Slugmass: overall formula of newton to slug is "mass (slug) = weight (N) ÷ gravity or acceleration (ft/s²)"; breaking it down: 1 Nweight → kgmass: m = W/g = 1/9.8 = 0.10204 kg and 1 slug = 14.5939 kg, ∴ 0.10204/14.5939 = 0.007 slugs; overall it's: 0.102kg/14.5939kg = 1N/(9.8m/s² x 14.5939kg) = 0.007 slugs
[1] Wikipedia
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