Weight Converter – Free Online Weight Conversion Calculator

Need a simple way to flip between grams, kilograms, pounds, ounces, stones, or tons?Our weight converter gives you instant, precise results powered by the International System of Units (SI) and NIST-aligned factors. Whether you’re prepping a recipe, printing shipping labels, tracking gym progress, or finishing a school lab, reliable weight conversion removes guesswork and keeps numbers consistent across metric and US customary systems.

Why Use a Weight Converter?

Manual math and rounded “rules of thumb” create errors that snowball on bigger quantities. A modern weight conversion calculator:

• applies exact factors (e.g., 1 lb = 0.45359237 kg, 1 oz = 28.349523125 g),
   
• lets you choose your precision and significant figures,
   
• supports scientific notation for very small or very large masses.

How the Weight Converter Works

1. Enter a value: Whole numbers or decimals.
    
2. Choose a starting unit: grams (g), kilograms (kg), milligrams (mg), micrograms (µg), pounds (lb), ounces (oz), stones (st), metric tons (t), short tons (US), or long tons (UK).
    
3. Pick a target unit: Convert in one click.
    
4. Copy/Share: Paste results into a recipe, spec sheet, shipping form, or lab report.

Under the hood, the calculator converts via the base SI unit, the kilogram, then maps to your target. This hub-and-spoke model keeps every pair consistent.

Units You Can Convert

• Metric (SI): microgram (µg), milligram (mg), gram (g), kilogram (kg), metric ton (t).
   
• Imperial/US Customary: ounce (oz), pound (lb), stone (st), short ton (US ton), long ton (imperial ton).
  This coverage makes the weight converter useful for e-commerce, manufacturing, fitness, and education.

Popular Weight Conversions Examples

• Pounds to Kilograms: 1 lb = 0.45359237 kg
  Example: 150 lb = 68.0388555 kg (round to 68.04 kg for 4 s.f.)
   
• Ounces to Grams: 1 oz = 28.349523125 g (exact).
  Example: 12 oz flour = 340.1942775 g (≈ 340.19 g).
   
• Stones to Pounds: 1 st = 14 lb.
  Example: 11 st = 154 lb (≈ 69.85 kg).
   
• Kilograms to Metric Tons: 1 t = 1000 kg.
  Example: 2.4 t = 2400 kg.
   
• Short Tons (US) to Pounds: 1 short ton = 2000 lb.
   Example: 3 short tons = 6000 lb. 

Formulas, Factors, and Accuracy

The core idea is simple:

target_mass = source_mass × (source_to_kg) × (kg_to_target)

Key exact factors aligned with BIPM/NIST definitions:

• 1 kg = 1000 g = 1,000,000 mg
   
• 1 lb = 0.45359237 kg
   
• 1 oz (avoirdupois) = 28.349523125 g
   
• 1 st = 14 lb
   
• 1 short ton (US) = 2000 lb; 1 long ton (UK) = 2240 lb
   
• 1 metric ton (t) = 1000 kg

Tip: Precious metals often use the troy ounce (ozt), which is 31.1034768 g different from the everyday ounce. A proper weight conversion calculator will label this clearly or keep it out of general conversions to avoid mistakes.

Rounding & Significant Figures About Weight Conversion

Match your output to your input. If a nutrition label shows 42 g, reporting 1.481104258 oz is overkill. Convert first, then round to the appropriate significant figures or decimal places. For lab work, choose the same precision as your instrument; for logistics, round to the nearest gram or ounce to keep packing lists neat.

Everyday Use Cases Where Weight Converter Used

• Cooking & Baking: Convert ingredients to grams or ounces for consistent results across recipes.
   
• Fitness & Health: Log body weight in kg while gym equipment reads in lb; compare stones to kilograms quickly.
   
• Shipping & E-commerce: Generate labels in kilograms while suppliers quote pounds; map carton weights to metric tons for freight.
   
• Manufacturing & QA: Switch between grams and ounces for parts and consumables; standardize BOMs and tolerance checks.
   
• Education & STEM: Keep units consistent in lab reports; practice dimensional analysis and unit conversion fluency.

Common Mistakes and How to Avoid Them

• Using approximate factors: Skip “2.2 lb = 1 kg” in serious work—use 1 kg = 2.20462262185 lb when high precision matters.
   
• Mixing mass and force: In physics contexts, weight (force) uses newtons (N). Everyday “weight” means mass; your converter assumes mass units unless stated.
   
• Rounding too early: Do the full conversion first, then round once at the end.
   
• Unit ambiguity: Make sure “ton” means metric, short, or long in your region or industry.

Weight Conversion Chart