PhysicsCalcs
Units & Conversions

Weight and Mass Converter

Convert kilograms, grams, pounds, ounces, stones, tons, troy ounces, and atomic mass units.

Interactive converter

Weight and Mass Converter

Convert kilograms, grams, pounds, ounces, stones, tons, troy ounces, atomic mass units, and more.

Mass is normally non-negative. Weight (force) depends on gravity — use the optional W = mg panel below.

From
To

Result

Enter a value and click Convert to see the conversion.

Quick Guide

  • Convert mass between metric, imperial, troy, and scientific units.
  • Expand W = mg to estimate weight force on Earth, Moon, or Mars.
  • Mass conversion is separate from weight — they use different quantities.

Table of Contents

Key Takeaways

  • Mass (kg) measures matter; weight (N) is the gravitational force on mass.
  • 1 kg = 1,000 g exactly; 1 lb = 0.45359237 kg exactly.
  • Troy ounces (oz t) differ from avoirdupois ounces — used for precious metals.
  • The unified atomic mass unit u ≈ 1.66054×10⁻²⁷ kg.
  • Use the optional W = mg panel to estimate weight force from mass.

What Is Mass?

Mass measures the amount of matter in an object. The SI unit is the kilogram (kg). This converter handles mass units only — not weight force, unless you use the optional W = mg panel.

Mass Conversion Formula

massB=massA×(factorA/factorB)mass_B = mass_A × (factor_A / factor_B)

All units convert through kilograms. Example: 1 lb = 0.45359237 kg, so 2 lb = 0.90718474 kg.

Mass vs Weight

W=m×gW = m × g

W = weight force (N), m = mass (kg), g = gravitational acceleration (m/s²). On Earth, g ≈ 9.80665 m/s². A 1 kg mass weighs about 9.81 N (2.20 lbf) on Earth but only 1.62 N on the Moon.

Unit Groups

Metric/SI units scale from attograms to exagrams. Imperial units include pounds, ounces, stones, and US/UK tons. Troy and apothecary units are used for precious metals and pharmacy. Scientific units include the unified atomic mass unit and particle masses from CODATA.

For volume-to-mass conversion you need density — see the Volume Converter for capacity units.

Common Mass Values

ContextMassKilograms
Paperclip≈ 1 g0.001 kg
Adult human≈ 70 kg70 kg
Car≈ 1.5 t1,500 kg
Earth≈ 1 M⊕≈ 5.972×10²⁴ kg

Examples

1 kg to g

1 kg = 1,000 g.

1 lb to kg

1 lb = 0.45359237 kg exactly.

1 troy oz to g

1 oz t ≈ 31.1034768 g.

1 u to kg

1 u ≈ 1.66053906660×10⁻²⁷ kg.

Common Mistakes

Confusing pounds (mass) with pound-force (force). Mixing troy and avoirdupois ounces. Using lb on a scale as mass without noting it measures weight force under standard gravity.

Limitations

Biblical and regional mass units are omitted. Astronomical masses are approximate. The W = mg panel uses a constant g — not suitable for precision gravimetry.

FAQ

What is the difference between mass and weight?›

Mass is the amount of matter (kg). Weight is the force gravity exerts on mass: W = mg (newtons).

How many grams in a kilogram?›

1 kg = 1,000 g exactly.

How many pounds in a kilogram?›

1 kg ≈ 2.20462 lb.

What is a troy ounce?›

1 troy ounce ≈ 31.1035 g, used for gold and silver. It differs from the avoirdupois ounce (28.35 g).

What is an atomic mass unit?›

1 u (Dalton) ≈ 1.66054×10⁻²⁷ kg — defined as 1/12 the mass of a carbon-12 atom.

What is a stone?›

1 stone = 14 lb, commonly used for body weight in the UK.

How do I convert pounds to kilograms?›

Multiply pounds by 0.45359237. Example: 100 lb ≈ 45.36 kg.

How do I convert stone to kg?›

1 stone = 14 lb = 6.35029318 kg exactly.

Metric ton vs US ton?›

1 metric ton (tonne) = 1,000 kg. 1 US short ton = 2,000 lb ≈ 907.185 kg.

Can I convert mass to weight here?›

Yes — expand the W = mg panel, enter mass and local gravity, and get weight in newtons and pound-force.

Sources

  1. BIPM: SI Brochure
  2. NIST: mass unit conversions
Manish Kumar

Author & technical reviewer

Manish Kumar

PhysicsCalcs tools are reviewed with an educational focus: clear formulas, transparent assumptions, and practical context for students and science learners.

Learn more about Manish