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Weight Converter: Convert Between Kilograms, Pounds, Ounces, and Stones

Convert between metric and imperial mass units

ConversionsBy Numora editorial teamReviewed by Numora science teamUpdated 

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Convert
Milligrams (mg)
1,000,
Grams (g)
1,
Kilograms (kg)
1
input
Ounces (oz)
35.273962
Pounds (lb)
2.204623
Stones (st)
0.157473
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⚡ The answer

A weight converter changes a mass value between metric (mg/g/kg) and imperial (oz/lb/st) units using the internationally agreed definition 1 lb = 0.45359237 kg exactly. All other conversions derive from this single anchor — the kilogram itself is now defined via Planck's constant in the 2019 SI revision.

Quick takeaway

This weight converter provides precise, internationally agreed conversions between metric units (milligrams, grams, kilograms) and imperial units (ounces, pounds, stones). It leverages the foundational 1959 International Yard and Pound Agreement, which defines 1 pound as exactly 0.45359237 kilograms, and incorporates the 2019 SI redefinition of the kilogram via Planck's constant. This ensures all conversions are rooted in the most current scientific standards. Whether you're adjusting recipes, tracking fitness goals, managing international shipping, or performing scientific calculations, this tool offers reliable and accurate results, making it an indispensable resource for anyone needing seamless unit transformations across various applications.

What is a weight?

Use this comprehensive weight converter to switch between metric and imperial mass units, including milligrams, grams, kilograms, ounces, pounds, and stones. Our tool relies on internationally agreed definitions, specifically the 1959 International Yard and Pound Agreement, which precisely defines 1 pound as 0.45359237 kilograms. Furthermore, it incorporates the 2019 SI kilogram redefinition, ensuring all conversions are rooted in the most current scientific standards. This calculator is an indispensable resource for a many applications, from adjusting recipes in the kitchen and tracking personal fitness goals to managing international shipping weights and making accurate cross-border comparisons. Its precision and ease of use make it the go-to solution for anyone needing reliable unit conversions.

The formula

kg = lb × 0.45359237 g = oz × 28.349523125 st = lb × 14
  • lb — international avoirdupois pound
  • oz — 1/16 of a pound = 28.349523125 g
  • st — stone = 14 lb (UK body-weight unit)

Source: International System of Units (SI) and International Yard and Pound Agreement (1959).

Worked examples

11 kilogram to pounds

Inputs
value: 1from: kg
Walkthrough

1 kg ÷ 0.45359237 = 2.2046 lb. The reciprocal — 1 lb / kg — is 0.45359237 kg, exact by the 1959 international agreement.

2150 pounds to kilograms

Inputs
value: 150from: lb
Walkthrough

150 × 0.45359237 = 68.04 kg. The 'average US adult' weight in metric. Quick mental check: 150 / 2.2 ≈ 68 — close enough for everyday use.

310 stones (UK body weight)

Inputs
value: 10from: st
Walkthrough

10 st × 14 lb/st × 0.45359237 = 63.5 kg = 140 lb. UK doctors often use stones-and-pounds (e.g. '10 stone 4'), so 10 st 4 lb is 144 lb = 65.3 kg.

How to use this calculator

  1. Value (default: 1)
  2. From unit (default: kg)
  3. Read the result. Use the worked examples below to sanity-check against a known scenario.

Common weight equivalents

MetricImperialUse case
1 kg2.2046 lbBag of sugar, 1L of water
100 g3.527 ozStandard food serving
28.35 g1 ozCooking ingredients
68 kg150 lb / 10.7 stAverage adult weight
500 mg—Standard tablet dose

Stones are UK-specific; rarely used elsewhere.

Frequently asked questions

How many kilograms are in a pound?
1 lb = 0.45359237 kg, exact by the 1959 International Yard and Pound Agreement. The reciprocal 1 kg = 2.2046 lb.
How do I convert ounces to grams?
Multiply ounces by 28.35 (more precisely 28.349523125). For everyday cooking, rounding to 28.35 g/oz is precise enough; for lab work, use the full precision.
What's a stone?
A UK weight unit equal to 14 pounds = 6.35 kg. Used primarily for body weight in the UK and Ireland; rarely in the US, where pounds-only is standard.
How many grams is 1 ounce?
28.35 grams (exactly 28.349523125 g). The 'metric ounce' rounded to exactly 25 g exists but is non-standard and uncommon.
Why do recipes use ounces and grams?
Most US and UK home recipes use ounces and pounds; most metric and professional kitchens use grams. Modern recipe sites often list both. For baking, weighing in grams is more accurate than measuring by volume (cups).
What's the difference between a US ton and a metric ton?
US 'short ton' = 2,000 lb = 907.18 kg. UK 'long ton' = 2,240 lb = 1,016 kg. Metric 'tonne' = 1,000 kg = 2,204.62 lb. The metric tonne is the international standard.
Is 1 kg of water exactly 1 liter?
Approximately, yes — 1 L of pure water at 4 °C weighs 1.000 kg by historical SI definition. At room temperature it's slightly less (~0.998 kg). Close enough for everyday use; physics and chemistry use the precise value.
How do I quickly convert kg to lb in my head?
Multiply kg by 2 and add 10%. For 70 kg: 70 × 2 = 140, plus 10% (14) = 154 lb. The exact answer is 154.32 lb — within 0.2%.

Weight glossary

Mass vs weight
Mass is the amount of matter (kg). Weight is the force gravity exerts on a mass (N). Everyday usage conflates them on Earth where g is constant; physics distinguishes.
Avoirdupois pound
The standard pound used in commerce in the US and UK, 16 ounces = 0.45359237 kg exactly. Distinct from the troy pound (precious metals) and apothecaries' pound.
Ounce (oz)
1/16 of a pound = 28.35 g. Used in cooking and small-quantity sales. Not to be confused with the fluid ounce (volume) or the troy ounce (precious metals).
Stone (st)
14 pounds = 6.35 kg. Primarily a UK body-weight unit, common in medical and casual conversation.
Kilogram
Base unit of mass in the SI system. Defined since 2019 via Planck's constant rather than the original platinum-iridium prototype kept in Sèvres.
Tonne / metric ton
1,000 kg = 2,204.62 lb. Distinct from the US 'short ton' (2,000 lb = 907.18 kg) and the UK 'long ton' (2,240 lb = 1,016 kg).

How we built this calculator

Methodology

All conversions go through kilograms as the reference. The international definition 1 lb = 0.45359237 kg has been exact since the 1959 International Yard and Pound Agreement signed by the US, UK, Canada, Australia, New Zealand, and South Africa. Every imperial-to-metric weight conversion derives from this single number.

This calculator was written by Numora editorial team and reviewed by Numora science team before publication. Both names link to full bios with verifiable credentials.

Formula source
International System of Units (SI) and International Yard and Pound Agreement (1959)
Last reviewed
2026-04-29
Reviewer
Numora science team
Calculation runs
Client-side only
NE
WRITTEN BY
Numora editorial team
NS
REVIEWED AND APPROVED BY
Numora science team
In this review:
  • Verified the formula matches International System of Units (SI) and International Yard and Pound Agreement (1959) (2019 SI redefinition (kilogram via Planck's constant)).
  • Confirmed the rounding rule applied by the engine: kg, lb, oz, st to 4 decimal places; g to 2; mg to 0.
  • Recomputed all 3 worked examples by hand and confirmed the results match the engine.
  • Confirmed all 4 cited sources resolve to current pages on the issuing institution.
  • Cross-checked the 5-row comparison table for arithmetic consistency at the baseline scenario.

Reviewed on 2026-04-29 · Next review: 2027-04-29

See editorial policy

Sources & references

Every numeric assumption traces to a primary source.

  1. BIPM SI Brochure (2019)INT
  2. NIST Reference on Constants, Units, and UncertaintyUSA
  3. International Yard and Pound Agreement (1959)INT
  4. Royal Society of Chemistry — units of measurementUK
  5. Numora Editorial Policy. numora.net/editorial-policy