⚖️ Weight & Mass Converter
Convert between kilograms, pounds, grams, ounces, stone, metric tons, troy ounces, carats, atomic mass units and 80+ weight and mass units — with Newton's second law, gravitational weight, slug, troy system, Planck mass & historical units explained in MathJax
🔄 Weight & Mass Unit Converter
🌍 All Units at Once
📖 How to Use This Weight & Mass Converter
-
1Filter by Unit Category (Optional)
Choose Metric/SI (kg, g, mg, µg, t, quintal), Imperial/US (lb, oz, stone, short ton, long ton, grain, dram, hundredweight), Troy System (troy oz, troy lb, pennyweight, carat, scruple), Asian (catty, tael, jin, momme, baht), Historical (talent, shekel, mina, libra, tola, pud), or Scientific (amu, dalton, electron mass, slug, Planck mass).
-
2Enter Your Mass Value
Type the numeric value. Works across the full range — from the Planck mass (2.18×10⁻⁸ kg — smallest meaningful mass in physics) to tonnes, kilotonnes, and beyond.
-
3Select From and To Units
Choose your source and target units. The result and exact conversion factor appear instantly in the fuchsia result box with a full formula.
-
4Use Quick-Convert Buttons
Preset buttons — kg↔lb, g↔oz, stone↔kg, troy oz→g — set both dropdowns instantly for the most searched weight conversions.
-
5View All Units & Copy
"All Units at Once" shows your mass in every supported unit simultaneously. Click "📋 Copy Result" for use in nutrition labels, shipping manifests, laboratory reports, or precious metal valuations.
📐 Weight & Mass Conversion Reference Table
| From | To | Multiply By | Mathematical Expression |
|---|---|---|---|
| 1 kg | lb | 2.204623 | \( 1\,\text{kg} = 1/0.45359237\,\text{lb} = 2.204622622\,\text{lb} \) |
| 1 lb | kg | 0.453592 | \( 1\,\text{lb} = 0.45359237\,\text{kg} \) (exact, 1959) |
| 1 oz | g | 28.34952 | \( 1\,\text{oz} = \tfrac{1}{16}\,\text{lb} = 28.349523125\,\text{g} \) (exact) |
| 1 troy oz | g | 31.10348 | \( 1\,\text{oz t} = 31.1034768\,\text{g} \) (exact) |
| 1 stone | kg | 6.350293 | \( 1\,\text{st} = 14\,\text{lb} = 6.35029318\,\text{kg} \) (exact) |
| 1 metric ton | kg | 1,000 | \( 1\,\text{t} = 10^3\,\text{kg} = 2{,}204.623\,\text{lb} \) |
| 1 short ton (US) | kg | 907.1847 | \( 1\,\text{ton (US)} = 2000\,\text{lb} = 907.18474\,\text{kg} \) |
| 1 long ton (UK) | kg | 1016.047 | \( 1\,\text{ton (UK)} = 2240\,\text{lb} = 1016.0469\,\text{kg} \) |
| 1 carat | g | 0.2 | \( 1\,\text{ct} = 0.2\,\text{g} = 200\,\text{mg} \) (metric carat, exact) |
| 1 grain | g | 0.064799 | \( 1\,\text{gr} = \tfrac{1}{7000}\,\text{lb} = 64.79891\,\text{mg} \) (exact) |
⚖️ Mass vs Weight — The Critical Physics Distinction
Mass and weight are two of the most commonly confused concepts in physics — and for good reason: in everyday English, "How much do you weigh?" and "What's your mass?" mean the same thing. But in science and engineering, they are fundamentally different quantities with different units, and confusing them can cause serious errors — as famously happened in 1999 when NASA lost the Mars Climate Orbiter because one engineering team used imperial units and another used metric, resulting in a $327 million spacecraft burning up in the Martian atmosphere.
\( W = mg \qquad \text{(weight = mass × gravitational field strength)} \)
\( g_{\text{standard}} = 9.80665\,\text{m/s}^2 \quad \text{(exact, CGPM 1901 — ISO 80000-3)} \)
\( g_{\text{Moon}} = 1.625\,\text{m/s}^2 \quad g_{\text{Mars}} = 3.721\,\text{m/s}^2 \quad g_{\text{Jupiter (equator)}} = 24.79\,\text{m/s}^2 \)
\( 1\,\text{kgf} = 1\,\text{kg} \times 9.80665\,\text{m/s}^2 = 9.80665\,\text{N} \qquad \text{(kilogram-force)} \)
🔬 The Kilogram — Redefinition of the SI Base Unit (2019)
The kilogram (kg) is the SI base unit of mass — and it underwent its most significant redefinition in over 130 years on 20 May 2019. For the previous 130 years, the kilogram was defined by a physical platinum-iridium cylinder called the International Prototype of the Kilogram (IPK), stored under three glass bells in a vault at the BIPM in Sèvres, France. Comparing the IPK with national copies showed troubling drifts of up to 50 µg over decades, creating measurement uncertainty.
\( h = 6.62607015 \times 10^{-34}\,\text{J·s} = 6.62607015 \times 10^{-34}\,\text{kg·m}^2\text{·s}^{-1} \quad \text{(exact, SI 2019)} \)
\( 1\,\text{kg} \equiv \frac{h}{6.62607015 \times 10^{-34}}\,\text{m}^{-2}\text{·s} \quad \text{(derived from fixed Planck constant)} \)
\( 1\,\text{lb} = 0.45359237\,\text{kg} \quad \text{(exact — 1959 International Avoirdupois Pound Agreement)} \)
\( 1\,\text{kg} = 1000\,\text{g} = 10^6\,\text{mg} = 10^9\,\text{µg} = 10^{12}\,\text{ng} \quad \text{(metric prefix chain, exact)} \)
\( m_{\text{Planck}} = \sqrt{\frac{\hbar c}{G}} \approx 2.176 \times 10^{-8}\,\text{kg} \approx 21.76\,\mu\text{g} \quad \text{(Planck mass — natural unit)} \)
🇺🇸 The Imperial & US Customary System — Pound, Ounce & Avoirdupois
The pound (lb) is the base unit of the US customary and imperial mass systems. Its name derives from the Latin libra pondo ("pound by weight"), which is why the chemical symbol for lead is Pb (plumbum) and why we abbreviate pound as "lb" even though there's no 'b' or 'l' in "pound." The avoirdupois system (from Old French "goods of weight") is the everyday system used for general trade.
\( 1\,\text{lb} = 16\,\text{oz} = 256\,\text{dr} = 7{,}000\,\text{gr} = 453.59237\,\text{g} \quad \text{(exact, 1959)} \)
\( 1\,\text{oz} = \tfrac{1}{16}\,\text{lb} = 28.349523125\,\text{g} \quad \text{(exact)} \qquad 1\,\text{gr} = \tfrac{1}{7000}\,\text{lb} = 64.79891\,\text{mg} \quad \text{(exact)} \)
\( 1\,\text{stone} = 14\,\text{lb} = 6.35029318\,\text{kg} \qquad 1\,\text{cwt (US)} = 100\,\text{lb} = 45.3592\,\text{kg} \)
\( 1\,\text{ton (US short)} = 2000\,\text{lb} = 907.18474\,\text{kg} \qquad 1\,\text{ton (UK long)} = 2240\,\text{lb} = 1016.0469\,\text{kg} \)
\( 1\,\text{metric ton} = 1000\,\text{kg} = 2204.623\,\text{lb} = 1.1023\,\text{US short tons} = 0.9842\,\text{UK long tons} \)
Problem: A person weighs 82 kg. Convert to pounds, stone (UK-style), and stone+pounds combined display.
Pounds: \( 82 \times 2.204622622 = \mathbf{180.779\,\text{lb}} \)
Stone (decimal): \( 180.779 \div 14 = \mathbf{12.913\,\text{stone}} \)
Stone + lbs (combined): 12 stone (= 168 lb) + remainder (180.779 − 168 = 12.779 lb) = 12 st 12.8 lb
Quick formula: \( \text{stone} = \lfloor m_{\text{lb}}/14 \rfloor \qquad \text{extra lb} = m_{\text{lb}} \bmod 14 \)
Context: In the UK, body weight is traditionally expressed as "stone and pounds" (e.g., 12 stone 13 lb for ~82 kg). In the US, body weight is in pounds (180 lb). In most of the world, it's kilograms (82 kg). A bathroom scale in the UK displays all three. This calculator converts between all three systems instantly.
💎 Troy Weight System — Gold, Silver & Precious Metals
\( 1\,\text{troy lb} = 12\,\text{oz t} = 240\,\text{dwt} = 5{,}760\,\text{gr} = 373.2417216\,\text{g} \quad \text{(exact)} \)
\( 1\,\text{troy oz} = \tfrac{1}{12}\,\text{troy lb} = 20\,\text{dwt} = 480\,\text{gr} = 31.1034768\,\text{g} \quad \text{(exact)} \)
\( 1\,\text{pennyweight (dwt)} = 24\,\text{gr} = 1.55517384\,\text{g} \)
\( \text{Troy oz vs avdp oz: } \frac{31.1035}{28.3495} = 1.09714... \approx 9.71\%\text{ heavier} \)
\( 1\,\text{troy lb} = 0.822857...\,\text{avdp lb} \quad \text{(troy lb is lighter than avoirdupois!)} \)
Problem: Gold spot price is $3,200 per troy ounce (April 2026). A gold bar weighs 400 troy oz. What is its mass in kg and value?
Mass in grams: \( 400 \times 31.1034768 = 12{,}441.4\,\text{g} \)
Mass in kg: \( 12{,}441.4 \div 1000 = \mathbf{12.441\,\text{kg}} \approx 12.4\,\text{kg (about a brick)} \)
Value: \( 400 \times \$3{,}200 = \mathbf{\$1{,}280{,}000} \) per bar — a "good delivery" London Bullion Market Association (LBMA) bar
Key insight: The standard 400-troy-oz gold bar (used by central banks) actually weighs about 27.4 lb (avoirdupois), not 400 lb — because "troy ounce" ≠ "avoirdupois ounce."
💍 The Metric Carat — Gemstones & Diamond Grading
The metric carat (ct) is the standard unit of mass for gemstones, defined as exactly 0.2 grams (200 milligrams). Do not confuse it with karat (fineness of gold alloys, e.g., 18 karat = 75% gold). The carat originated from the carob seed (Ceratonia siliqua), which was traditionally used as a counterweight because of its remarkably uniform mass (~200 mg).
\( 1\,\text{ct} = 0.2\,\text{g} = 200\,\text{mg} \quad \text{(metric carat, exact — adopted 1907, CGPM)} \)
\( 5\,\text{ct} = 1\,\text{g} \qquad 1\,\text{kg} = 5000\,\text{ct} \quad \text{(clean decimal relationship)} \)
\( 1\,\text{ct} = 100\,\text{points} \qquad \text{(points used for diamonds below 1 ct: 0.50 ct = 50 points)} \)
\( \text{Gold karat: } K = \frac{24 \times m_{\text{Au}}}{m_{\text{total}}} \qquad \text{(18K = 75\% Au = 18/24 gold fraction)} \)
⚛️ Atomic Mass Unit (amu) & the Dalton
\( 1\,\text{u} = 1\,\text{Da} = \tfrac{1}{12} m\left({}^{12}\text{C}\right) = 1.66053906660 \times 10^{-27}\,\text{kg} \quad \text{(CODATA 2018)} \)
\( m_{\text{proton}} = 1.007276467\,\text{u} = 1.67262 \times 10^{-27}\,\text{kg} \)
\( m_{\text{neutron}} = 1.008664916\,\text{u} = 1.67493 \times 10^{-27}\,\text{kg} \)
\( m_{\text{electron}} = 5.485799 \times 10^{-4}\,\text{u} = 9.10938 \times 10^{-31}\,\text{kg} \)
\( 1\,\text{slug} = 1\,\text{lbf·s}^2/\text{ft} = 14.59390\,\text{kg} \quad \text{(imperial mass unit — mass that accelerates 1 ft/s² per 1 lbf)} \)
⚖️ Real-World Mass Reference Table
| Object | Mass (kg) | Mass (lb) | Notes |
|---|---|---|---|
| 🦠 Bacterium (E. coli) | ~10⁻¹⁵ | ~2×10⁻¹⁵ | ~1 picogram |
| 🧫 Human cell | ~10⁻¹² | ~2×10⁻¹² | ~1 nanogram |
| 💊 Aspirin tablet | 0.000325 | 0.000716 | 325 mg standard dose |
| 🍎 Apple (medium) | 0.182 | 0.40 | ~6.4 oz |
| ⚽ Football (FIFA) | 0.430 | 0.948 | 410–450 g specification |
| 👤 Adult human (avg.) | ~70 | ~154 | Global average 2016: 62 kg |
| 🚗 Compact car | ~1,400 | ~3,086 | Kerb weight, 1.4 t |
| 🐘 African elephant (bull) | ~6,000 | ~13,228 | Largest land animal |
| 🚌 Loaded bus | ~18,000 | ~39,683 | 18 metric tonnes GVW |
| 🚢 Supertanker (ULCC) | ~500×10⁶ | ~1.1×10⁹ | 500,000 DWT laden |
🌏 Asian Weight Units — Traditional & Modern
Chinese Units — Jin, Liang, Tael
Jin (市斤): 500 g = 1.102 lb (modern PRC standard since 1930s). Liang (两): 50 g = 1/10 jin. Tael (两 Hong Kong): 37.5 g (precious metals). Hong Kong gold tael differs from mainland liang. Chinese buyers still request gold in taels; dealers quote in troy oz for international settlements.
Japanese Units — Momme & Kan
Momme (匁): 3.75 g (now used only in the silk and pearls trade internationally). Kan (貫): 3.75 kg = 1,000 momme. Japan metricated in 1958; the momme remains in pearl jewellery globally as a quality-weight standard. Pearl weight is still quoted in momme in international trade catalogues.
Thai Baht Weight
Baht (บาท): 15.244 g — Thailand's traditional gold weight unit (not the currency, though both share the same name historically). Thai gold is sold by baht-weight in traditional Thai shops; international gold is priced per troy oz. 1 troy oz ≈ 2.04 baht (weight). Thai gold is typically 96.5% pure (23 karat).
Indian Units — Tola, Seer, Maund
Tola: 11.6638 g — traditional Indian gold measure, used across South Asia. Seer: 933.1 g (varies by region). Maund: 37.324 kg (40 seer). India still quotes gold in tolas in rural markets; urban India uses grams. 1 tola ≈ 10 g in common practice.