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Weight Converter

How do I convert weight units?

How it is calculated

Every unit is defined by a fixed factor to the kilogram: base_kg = value × factor_from, then result = base_kg ÷ factor_to. The factors used are 1 lb = 0.45359237 kg, 1 oz = 0.028349523125 kg, 1 st = 6.35029318 kg, 1 t = 1000 kg, 1 g = 0.001 kg and 1 mg = 0.000001 kg. The value is the amount in the unit you choose under from; if that unit is not recognised the tool falls back to kilograms. All seven units are shown at once, each with two decimals, and more digits below 1.

Worked example

Convert 150 lb. Step 1: 150 × 0.45359237 = 68.04 kg (68.038855 before rounding). Step 2: divide by each factor: 68.038855 ÷ 0.001 = 68,038.86 g; ÷ 1000 = 0.06804 t; ÷ 0.028349523125 = 2,400.00 oz; ÷ 6.35029318 = 10.71 st. So 150 lb equals 68.04 kg, 2,400.00 oz and 10.71 st.

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Common mistakes

  • Leaving the from unit on kilograms while typing a pound value, which makes the answer roughly 2.2 times too large.
  • Confusing the tonne (t, 1000 kg) with the imperial ton; this tool only uses the metric tonne.
  • Reading stone as a decimal: 10.71 st is 10 stone and about 10 lb (0.71 × 14), not 10 stone 71 lb.
  • Trusting a rounded figure for further maths; convert from grams or kilograms instead.
  • Mixing up ounces of weight (oz) with fluid ounces of volume; they are not interchangeable.

About this calculator

This tool converts a mass value — what everyday usage calls weight — between units such as kilograms, grams, tonnes, pounds, ounces and stone, applying the exact fixed ratio that relates each unit pair rather than an estimate. Unlike some conversions, this conversion is purely mathematical: these are fixed ratios between units of mass, so the result does not shift with location the way a weight reading does, nor with temperature or anything else.

It is used constantly for cooking and baking when a recipe uses a different unit system than what's on hand, for tracking body weight or fitness progress when switching between kilograms and pounds, and for shipping or luggage limits that are often stated in one system while a scale reads in another.

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Comments (1)

  • Editorial team

    Results use two decimals, and more below 1, so read fine work from the closest unit. The oz here is the avoirdupois ounce for weight, not a fluid ounce, and a stone is 14 pounds. For body weight, pounds and stones to kilograms is the usual need. Which unit should we add next?

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