What is weight conversion?

Weight (technically mass, in scientific terms) conversion translates measurements between metric units (kilograms, grams, milligrams, tonnes) and imperial/US units (pounds, ounces, stones, tons). The need for conversion arises from international product specifications, fitness tracking, cooking recipes, shipping calculations, and medical dosing. While most of the world uses metric (kg), the US uses pounds and the UK uses ‘stones’ for body weight (where 1 stone = 14 pounds, so a person says ‘I weigh 11 stone’ rather than ‘154 pounds’). Many scientific contexts also use metric exclusively. This converter handles all common weight units instantly with full precision using internationally-defined conversion factors.

How to use this tool

1. Enter the value — Number to convert. Can be a decimal (e.g. 70.5) or integer.
2. Select ‘from’ unit — Choose what unit your value is in – kg, g, mg, tonnes, pounds, ounces, stones, US tons, UK long tons.
3. Read all conversions — Every other unit shows the equivalent value, updated instantly as you type.

Weight conversion factors

All metric ↔ imperial conversions use international standards:

• 1 kg = 2.20462 pounds = 35.274 ounces
• 1 pound = 0.453592 kg = 16 ounces
• 1 ounce = 28.3495 grams
• 1 stone = 14 pounds = 6.35029 kg (UK body weight)
• 1 kg = 1,000 g = 1,000,000 mg = 0.001 metric tonnes
• 1 metric tonne (t) = 1,000 kg = 2,204.62 pounds
• 1 US ton = 2,000 pounds = 907.185 kg (also called ‘short ton’)
• 1 UK long ton = 2,240 pounds = 1,016.05 kg

Worked example: 70 kg in pounds:

• 70 × 2.20462 = 154.32 pounds
• Or in stones: 154.32 / 14 = 11.02 stone (UK style: ‘about 11 stone’)

Examples

• 70 kg to pounds: 154.32 lb (typical adult man)
• 1 pound to grams: 453.59 g (recipe conversions)
• 500 mg to ounces: 0.0176 oz (medication dosing)
• 200 g (5 medium apples) to ounces: 7.05 oz
• 10 stone to kg: 63.5 kg (UK body weight)
• 2,000 pounds shipping (1 US ton) to kg: 907 kg
• Newborn baby 7.5 lb to kg: 3.4 kg (standard pediatric)

Tips & best practices

• For body weight, memorize: 1 kg ≈ 2.2 lb. So 70 kg ≈ 154 lb, 80 kg ≈ 176 lb
• For cooking ingredient conversions, 1 oz = 28 g, so a 4 oz portion is ~113 g
• For US vs UK confusion: US ton (2,000 lb / 907 kg) is 10% smaller than UK long ton (2,240 lb / 1,016 kg) – always check which system the spec uses
• Shipping uses ‘metric tonne’ = 1,000 kg internationally; US domestic shipping uses ‘short ton’ = 2,000 lb
• Body weight in UK conversation: ’11 stone’ = 154 lb = 70 kg. 1 stone increments are about 6.4 kg
• For medication, never convert between mg and g without double-checking – dosing errors are dangerous
• Newborn weight is the only context where ‘pounds and ounces’ is universally used: ‘7 lb 3 oz’ (7 pounds 3 ounces)

Limitations & notes

This converter uses standard internationally-defined factors. Some specialty industries use unique units not included here: troy ounces for precious metals (1 troy oz = 31.1 g, different from regular oz), grains in firearms (1 grain = 0.0648 g), carats for gemstones (1 carat = 0.2 g). For those, search ‘troy ounce to gram’ specifically.

Frequently Asked Questions

How do I convert pounds to kg quickly mentally?

Divide pounds by 2.2, or multiply by 0.45. For example: 100 lb / 2.2 = 45.4 kg. For most everyday purposes, 2.2 lb per kg is precise enough.

What’s the difference between weight and mass?

Scientifically: weight = mass × gravitational acceleration. On Earth, mass and weight are proportional (a 1 kg mass weighs 9.81 newtons). In everyday English, ‘weight’ usually means mass – we say ’70 kg’ which is mass, not weight. The astronaut on the moon has the same mass (70 kg) but lower weight (115 newtons instead of 686).

Why does the UK use stones for body weight?

Historical convention. The stone (14 lb) was used since the 14th century for trade and is still common in informal British conversation about body weight: ‘I weigh 11 stone 6’. Medical contexts in the UK now use kg (since 2000s). Most other countries use either kg (metric world) or just pounds (US).

How accurate is this conversion?

Exact – uses international conversion factors defined by the National Institute of Standards and Technology (NIST). The browser computes with 15-17 significant digits of precision, far beyond what anyone needs for everyday or scientific work.

What’s the difference between US ton and metric tonne?

US ton (short ton) = 2,000 pounds = 907.185 kg. Metric tonne (also called ‘tonne’ or ‘metric ton’) = 1,000 kg = 2,204.62 pounds. Metric tonne is about 10% larger. Shipping internationally usually uses metric tonne; US trucking uses short ton.

How do I convert dry vs liquid weight?

Weight units (kg, lb, oz) measure mass and work for any substance. For COOKING, recipes sometimes give weight (‘200 g flour’) or volume (‘1 cup flour’) – those need a substance-specific density to convert (1 cup flour = 120-130 g depending on packing). Use a kitchen scale for accuracy.

Why does converting milligrams to ounces give such tiny numbers?

Because ounce is a relatively large unit compared to milligrams. 1 ounce = 28,350 mg. A typical 500 mg pill = 0.0176 oz. Pharmacies use milligrams or micrograms for medication dosing because ounces are too large to be useful at small scales.

Related tools

Length Converter · Volume Converter · Temperature Converter · Area Converter