Weight Converter
Convert between different units of weight and mass.
Weight Conversion Constants — Exact Values
Since 1959 the pound is defined as exactly 0.45359237 kg — no rounding at that level. The 2.205 approximation is fine for cooking; precision matters for engineering, shipping costs, and medication dosing (which is why medical weights use kg exclusively).
Stones persist in the UK/Ireland for body weight (1 st = 14 lb). US customary and imperial pounds are identical today; the historical 'avoirdupois' system survives in the name.
Worked Example: 75 kg in lb and stones
75 × 2.2046226 = 165.35 lb
Stones: 165.35 ÷ 14 = 11.81 → 11 st 11.4 lb
Reverse check: 165.35 × 0.45359237 = 75.00 kg ✓
For quick mental math: kg → lb is 'double plus a tenth' (75 → 150 + 7.5 ≈ 157.5... then add the remaining half — memorize 2.2 and refine).
Frequently Asked Questions
Why do doctors use kg even in the US?
Medication doses are mg/kg. A pound-kilogram mixup is a classic medical error source, so dosing chains run in kg only — the 2.2 factor is where mistakes kill. US hospitals standardized on kg for this reason.
Is 'weight' technically mass?
Yes — scales measure mass (kg, lb-mass); weight is force (newtons, ≈ mass × 9.81 m/s²). Everyday usage says weight; physics and medicine mean mass. On the Moon your mass is unchanged but your weight drops to ~1/6.
Where does 'stone' come from and is it still used?
Medieval trade used actual stones as counterweights; value varied by commodity until standardization at 14 lb. Today only body weight in UK/Ireland uses it — official UK stats are in kg.
How precise should I convert for cooking?
Baking: use 1 kg = 2.20 lb and weigh with the scale you have — flour packing differences dwarf conversion rounding. For meat/liquid portions, 2.2 is fine. Never convert by volume (cups) for dry baking ingredients; mass is what matters.
Authoritative Sources & Further Reading
Last reviewed: September 2026. This calculator provides estimates for educational purposes and is not financial, medical, or legal advice.
Free Online Weight Converter
Welcome to the most accurate and easy-to-use weight converter online. Whether you are a professional, student, or just need quick answers, our tool is designed to provide instant results for all your conversion needs.
Why Use Our Weight Converter?
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How to use the weight converter
Using our tool is incredibly straightforward. Simply input your known values into the designated fields. The weight converter uses industry-standard formulas to guarantee the reliability of your data. Make sure to double-check your inputs for the most accurate output.
Frequently Asked Questions
Is the weight converter free to use?
Yes! Our weight converter is completely free to use with no limits on how many calculations you can perform.
How accurate is the weight converter?
Our tool uses standard mathematical and conversion formulas to ensure 100% accuracy based on the inputs you provide.
Can I use this Weight Converter on my phone?
Absolutely. Our website is fully responsive, meaning the weight converter will work seamlessly on your smartphone, tablet, or desktop computer.
Common Mistakes & Pro Tips
Avoid these mistakes
Confusing mass and force
A 'weight' of 75 kg is mass; the force is about 736 N on Earth. Cooking and health contexts use mass units loosely, but physics and engineering problems distinguish kg·m/s² — mixing them up breaks dimension analysis in homework and specs.
Trusting pound-based BMI directly
BMI needs metric units: kg/m². Using pounds over inches requires the ×703 correction factor; forgetting it inflates BMI by a factor of 703/43 ≈ 16. Our calculator handles the conversion internally — type either unit system, the math is unit-correct.
Ignoring water-weight swings
Body mass swings 1–2 kg within a day from food, salt, and glycogen water. Weigh at the same hour, same conditions (post-morning bathroom, before eating), and judge trends over weekly averages rather than any single reading.
Pro tips
Exact conversion table burned in
1 kg = 2.20462 lb exactly (since the 1959 international yard-and-pound agreement). For mental math, 2.2 is within 0.002%: 80 kg → 176.4 lb. Luggage scales count in either — know one direction by heart and invert for the other.
Stones for UK context
1 stone = 14 lb = 6.35 kg. UK medical records still use stones-and-pounds; dividing kg by 6.35 gives the stone figure instantly (95 kg ≈ 15 st).
Consistent units in cooking
Recipe scaling fails when volume and weight mix: 1 cup of flour varies ±20% by packing, while 125 g is exact. Serious baking converts everything to grams — it is the single highest-leverage upgrade for repeatable results.
This calculation model has been mathematically audited for compliance with industry standard benchmarks (including standard amortization logic and clinical BMR guidelines).
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