About Mass & Weight Converter — kg, lb, oz, Tons & Stone
The mass and weight converter translates a mass between the units that share one job site: kilograms and metric tonnes from SI drawings and material data, pounds and ounces from US datasheets and shipping papers, stone from UK body-weight convention, and the three tons that refuse to be one unit — the US short ton (2,000 lb), the UK long ton (2,240 lb), and the metric tonne (1,000 kg). Every conversion runs through the SI base unit — the kilogram — using the exact avoirdupois definitions published in NIST SP 811 Appendix B, so a chain like kg → lb → kg returns exactly where it started.
The anchors worth memorizing: 1 lb = 0.45359237 kg exactly (the 1959 international pound definition), so 1 kg ≈ 2.20462 lb; 1 stone = 14 lb = 6.35029 kg; and the tons sit at 907.185 kg (short), 1,016.05 kg (long), and 1,000 kg (metric) — close enough to be confused, far enough apart to sink a load rating. Strictly, these are units of mass; "weight" in everyday and commercial use means the same thing, and the converter follows that usage while never touching gravity.
How It Works
- Enter the mass, pick the unit it is currently in ("from"), and pick the unit you need ("to"). The headline shows the converted value; the table below it shows the same mass in all eight units at once, so you can lift whichever one the next document needs.
- Every conversion is value × (kilograms per from-unit) ÷ (kilograms per to-unit). The factors are exact by definition: the international avoirdupois pound is 0.45359237 kg, and the ounce, stone, and both tons are exact multiples of it (NIST SP 811 Appendix B; the stone via NIST Handbook 44 Appendix C).
- Displayed values are rounded to 6 significant digits. That is display rounding only — the underlying conversion is done in full double precision, which is why round-trips return your original number.
- Watch the three-ton trap: an unqualified "ton" in a US spec is usually the 2,000 lb short ton, in older UK documents the 2,240 lb long ton, and in SI paperwork the 1,000 kg tonne. The converter names all three explicitly so the 10% short-vs-long gap never hides in a word.
Worked Example
A US rigging plan lists a component at 10 lb and the crane submission wants kilograms. Through the kilogram: 10 lb × 0.45359237 kg/lb = 4.53592 kg — the exact definition, no rounding loss. The same mass is 160 oz and 0.714286 stone; going the other way, a 1 tonne (1,000 kg) pallet is 2,204.62 lb, which is 1.10231 short tons — over the nominal "1 ton" rating of a light-duty hoist even though it is exactly one metric tonne.
kg to lbs conversion chart (with oz and stone)
Common kilogram values converted to pounds, ounces, and stone with the exact NIST SP 811 factor (1 lb = 0.45359237 kg), shown to 6 significant digits — exactly what the converter outputs for the same inputs.
| Mass | lb | oz | stone |
|---|---|---|---|
| 1 kg | 2.20462 | 35.274 | 0.157473 |
| 5 kg | 11.0231 | 176.37 | 0.787365 |
| 10 kg | 22.0462 | 352.74 | 1.57473 |
| 25 kg | 55.1156 | 881.849 | 3.93683 |
| 50 kg | 110.231 | 1,763.7 | 7.87365 |
| 100 kg | 220.462 | 3,527.4 | 15.7473 |
Formulas
- Conversion through the base unit
x = value × f_from ÷ f_to- Kilograms per unit (the factor table)
lb 0.45359237 · oz 0.028349523125 · stone 6.35029318 · short ton 907.18474 · long ton 1,016.0469088 · tonne 1,000- The everyday anchors
1 kg ≈ 2.20462 lb; 1 lb = 16 oz; 1 stone = 14 lb; 1 tonne ≈ 1.10231 short tons
Standards & References
- NIST SP 811, Guide for the Use of the International System of Units, Appendix B — conversion factors (pound 4.535924×10⁻¹ kg, exact 0.45359237 per footnote 22; ounce 2.834952×10⁻² kg; short ton 9.071847×10² kg; long ton 1.016047×10³ kg)
- NIST Handbook 44 (2024), Appendix C — British units: 14 pounds = 1 stone, giving 6.35029318 kg exactly
- Displayed to 6 significant digits; conversions computed in full double precision
Frequently Asked Questions
How do I convert kg to lbs?
Divide kilograms by 0.45359237 (the exact definition of the pound), or multiply by 2.20462 for everyday work. So 10 kg ≈ 22.046 lb and 100 kg ≈ 220.46 lb. Going the other way, multiply pounds by 0.45359237 to get kilograms exactly.
What is the difference between a short ton, a long ton, and a metric tonne?
Three different units that share a name. The US short ton is 2,000 lb = 907.185 kg; the UK long ton is 2,240 lb = 1,016.05 kg; the metric tonne is 1,000 kg = 2,204.62 lb. The spread between short and long is 10.7% — enough to overload a hoist or misprice a freight contract — so the converter lists all three explicitly and never abbreviates any of them to just "ton".
Is this converting mass or weight?
Mass. Kilograms, pounds, ounces, stone, and tons are all units of mass, and converting between them is pure multiplication with no gravity involved. In everyday and commercial language "weight" means mass — a shipping weight in lb converts to kg with this tool exactly. Weight as a force (what a scale spring actually feels) is mass × g and lives in newtons or pounds-force; use the force converter for that.
How many pounds is a stone?
Exactly 14 lb, which is 6.35029318 kg. The stone survives mainly in UK and Irish body-weight usage — an "11 stone" person is 154 lb ≈ 69.9 kg. It is defined through the same international pound as every other avoirdupois unit, so the conversion is exact.
Why do round-trip conversions return my exact starting number?
Because every conversion runs through the kilogram in full double precision and only the display is rounded to 6 significant digits. kg → lb → kg is (value × 1 ÷ 0.45359237) × 0.45359237, which cancels to the starting value to within one floating-point ulp. If you re-enter the rounded display value instead, you carry the display rounding with you — copy from the all-units table for exact chains.