Weight Unit Converter Guide
Mass vs weight, the metric–imperial bridge, and the three ton definitions you need to keep straight.
Convert between every common mass unit and know which "ton" you are actually using.
Weight conversion is easy until you hit "ton" — which has three different values depending on where you are — or until someone asks whether you mean mass or force. This guide covers the common units, the exact bridges, and the two places the naming trips people up.
Part of: Unit Conversion Tools
Quick answer
Convert between every common mass unit and know which "ton" you are actually using.
Key points
- ▸ Metric: 1 kg = 1,000 g. 1 tonne (metric ton) = 1,000 kg.
- ▸ Imperial: 1 lb = 16 oz. 1 stone = 14 lb. 1 short ton (US) = 2,000 lb. 1 long ton (UK) = 2,240 lb.
- ▸ Cross-system anchors: 1 lb = 0.45359237 kg exactly. 1 oz = 28.349523125 g exactly. 1 kg ≈ 2.2046 lb.
- ▸ Three tons: metric tonne 1,000 kg = 2,204.62 lb; US short ton 2,000 lb = 907.185 kg; UK long ton 2,240 lb = 1,016.047 kg. The three differ by up to 12%.
- ▸ Mass vs weight: the tool reports mass (kg, lb). Weight (force) is mass × g, measured in newtons. Day-to-day the words are interchangeable; in physics they are not.
- ▸ Stone is alive in the UK and Ireland for body weight. 11 st 3 lb is 157 lb or 71.21 kg.
How to
- Enter the mass value in the source unit.
- Pick the target unit — watch for tonne vs short ton vs long ton.
- Read the result at six decimals; round to sensible places for the context (kg body weight: one decimal; shipping: whole numbers).
- If you see "ton" in a spec sheet, confirm which ton before converting.
Examples
- 180 lb to kg180 × 0.45359237 = 81.647 kg. Typical adult weight.
- 11 st 3 lb to kg11 × 14 + 3 = 157 lb. 157 × 0.45359237 = 71.21 kg.
- 2 short tons to metric tonnes2 × 907.185 / 1,000 = 1.814 tonnes — a US truck of gravel weighs about 1.8 metric tonnes.
When to use which tool
- CYAN · STABLE — Cooking, fitness, body weight — one or two decimals is enough.
- GOLD · GUARDED — Shipping, commercial weighing — keep four decimals and name the ton explicitly.
- MAGENTA · CRITICAL — Metrology, calibration, scientific mass measurement — carry the full 0.45359237 factor and round only at report time.
Related
Frequently asked questions
› Are mass and weight actually different?
Yes. Mass is the amount of matter (kg, lb). Weight is the force gravity exerts on that mass (newtons). On Earth the distinction rarely matters; on the Moon a 70 kg person still has 70 kg of mass but weighs only about one-sixth as much.
› Which ton is the default in US shipping?
US freight uses the short ton (2,000 lb) unless the label says "metric tonne" or "MT." International shipping almost always means the metric tonne.
› Why is 1 lb defined in terms of kg? Troubleshooting
The international pound was redefined as exactly 0.45359237 kg in 1959 so every English-speaking country uses the same value. The kilogram is the primary SI unit.
› How should I use this guide with a Kefiw tool? How-to
Use the guide as the plan and the linked Kefiw tool as the check. Read the steps first, try the move manually, then use the tool to compare outputs, catch edge cases, and decide whether the result actually fits your task.
› What mistake do tool guides help avoid? Troubleshooting
Tool guides help avoid using a utility mechanically without understanding what you are trying to accomplish. Most word, writing, and text utilities are fast, but speed can hide context mistakes. Know whether you are solving a puzzle, cleaning copy, drafting a line, or checking a rule.