Weight Converter

Weight converter: pounds, kilograms, ounces, grams, and stones. Free weight converter with the formula shown - runs entirely in your browser, no signup.

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Last verified July 2026

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What does this converter do?

Weight converter: pounds, kilograms, ounces, grams, and stones. Free weight converter with the formula shown - runs entirely in your browser, no signup.

  • 1 pound = 0.4536 kilogram · 1 stone = 6.35 kilogram · 1 ounce = 28.35 gram
  • All conversions route through the kilogram as the base unit, so every pair of units agrees regardless of which two you enter.
  • Standard factors are shown in the formula panel at the precision the calculator actually uses, so the arithmetic and the panel agree.
Pounds to kilograms: the 1959 exact definition of the pound
1 pound is exactly 0.45359237 kilograms by international agreement.

Reference factors (mass)

Exact factors in terms of the kilogram, from NIST standards:

  • 1 milligram = 1e-06 kilogram
  • 1 gram = 0.001 kilogram
  • 1 ounce = 0.0283495 kilogram
  • 1 pound = 0.453592 kilogram
  • 1 kilogram = 1 kilogram
  • 1 stone = 6.35029 kilogram
  • 1 metric ton = 1000 kilogram
Formula & evidence

How this calculator works

Reviewed 2026-09-20 · BoringToolsKit Editorial Team

Formula

Value x (kilograms per source unit) / (kilograms per target unit), using exact factors: pound 0.45359237, ounce 0.028349523, stone 6.35029, tonne 1000.

Worked example

1 pound = 0.4536 kilogram · 1 stone = 6.35 kilogram · 1 ounce = 28.35 gram

Sources

Sources support the method, terminology, or planning context. Editable assumptions remain your responsibility.

Assumptions to verify

  • Inputs are treated as exact decimal values.
  • Standard (not historical or survey) unit definitions are used.
  • The calculation uses the factors at the precision shown in the formula panel; rounding beyond that is display-only and adds no accuracy.

Frequently asked questions

Why convert through kilogram instead of directly?

Routing every unit through a single base (kilogram) means each unit needs only one exact factor against the standard, and any pair combines cleanly. Direct pair factors drift apart over time in hand-maintained tables; a base-unit graph cannot.

Where do these exact factors come from?

From published standards (NIST: SI SP 330 mass definitions). Units like the inch are defined exactly (1 in = 2.54 cm since 1959), so conversions between standard units are exact, not approximate.

How many decimal places should I trust?

The math is exact to the precision shown. The practical limit is your input: a tape measure is only good to ~1 mm and a kitchen scale to ~1 g, so 3–4 significant figures already exceeds the measurement's own accuracy.

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Cite this tool

BoringToolsKit. “Weight Converter.” boringtoolskit.com/weight-converter/ (reviewed 2026-09-20). Free to reference in articles, syllabi, and answer posts with a link.

Privacy: Inputs and results stay in this browser. Conversion runs locally in your browser; review the output before relying on it.

Worked example: 154 lb in stone and kilograms

Take 154 lb, the rounded weight of a 70 kg adult. Converting to stone uses the factor 6.35029 kg per stone: multiply 154 by 0.45359237 to get 69.85322498 kg, then divide by 6.35029. That gives 11.00000548 stone, which the calculator displays as 11.00 stone. The tiny overshoot exists because the page's stone factor (6.35029) is the 6.35029318 kg that exactly 14 pounds would produce, rounded to five decimal places; the error is about 5 grams per stone, invisible at two decimals.

The same input in kilograms needs no division, since pounds convert straight down the factor table: 154 x 0.45359237 = 69.85322498, shown as 69.85 kg. Going the other direction, 69.85 kg back to pounds gives 154.014 lb, so a round-trip through the two-decimal display loses roughly 0.01 lb. For any stated tolerance tighter than that, keep the full 8-significant-figure factor rather than a rounded 0.454.

Where the display rounds and why it matters

The formatter has three tiers: values of 1 kg or more print 2 decimals, smaller values print 4 significant figures, and anything at 1000 or above prints with no decimals at all. That last tier silently rounds big conversions: 2 metric tons to pounds is 4409.2488 lb, but the result box shows 4,409 lb, a 0.25 lb swing that matters for freight or recipe batching. Anything under a gram lands in the 4-significant-figure tier, so 200 mg converts to 0.007055 oz; the milligrams digit itself is real, but trailing precision is capped at 4 figures.

Two inputs are rejected outright. A zero or negative value returns the 'Value must be above 0' message, since mass factors only scale positive numbers. Extreme magnitudes still compute but can overflow to Infinity for absurd inputs, which the formatter then prints literally. Practical rule: for work that needs more than 2 decimals on large values, convert in the smaller unit (tons to pounds minus the rounding, or compute pounds as 2000 x 2.20462262 per ton by hand) and treat the on-page figure as a check, not the record.