Are "weight" and "mass" the same?

Not strictly in physics. Mass is a constant property of an object (measured in kg). Weight is the force acting on that mass due to gravity (measured in newtons). On Earth the numeric value is almost identical because g ≈ 9.81 m/s². In everyday use they are treated as synonyms.

What’s the difference between pound (avoirdupois) and troy pound?

Regular pound (lb, avoirdupois) = 453.592 g used for everyday weight. Troy pound = 373.242 g used only for precious metals and gems. A "troy ounce" (oz t) is also slightly heavier than a regular ounce: 31.103 g vs 28.349 g. The calculator uses avoirdupois unless specified otherwise.

What’s a "tonne" versus a "ton"?

Metric tonne (t) = 1,000 kg. The US uses "short ton" (2,000 lb ≈ 907.185 kg). The UK uses "long ton" (2,240 lb ≈ 1,016.047 kg). The calculator shows metric tonnes unless you pick the US variants.

How accurate is the conversion?

The calculator uses exact factors defined by BIPM: 1 lb = 0.453 592 37 kg (since 1959). Display precision is 6+ decimals for small values and rounds to a readable count for large values. Measurement device inaccuracy (bathroom scales, etc.) is usually larger than the conversion error.

Weight Converter - kg, lbs, oz, grams

Unit	Kilogram (kg)	Gram (g)	Pund (lb)	Ounces (oz)
1 kg	1	1000	2.20462	35.27396
1 g	0.001	1	0.00220	0.03527
1 lb	0.45359	453.59237	1	16
1 oz	0.02835	28.34952	0.0625	1
1 st (stone)	6.35029	6350.293	14	224

Unit

Kilogram (kg)

Gram (g)

Pund (lb)

Ounces (oz)

1 kg

1000

2.20462

35.27396

1 g

0.001

0.00220

0.03527

1 lb

0.45359

453.59237

1 oz

0.02835

28.34952

0.0625

1 st (stone)

6.35029

6350.293

224

How weight conversion is calculated

All weight conversions are based on the international yard and pound agreement of 1959, which defines one pound (lb) as exactly 0.45359237 kilograms. Stones and ounces are sub-units of the pound.

1 stone (st) = 14 pounds (lb)
1 pound (lb) = 16 ounces (oz)
1 kilogram (kg) = 1000 grams (g)

About this tool

Weight and mass conversion between the metric system (grams, kilograms, tonnes) and imperial units (ounce, pound, stone). The SI unit is the kilogram (kg); all other mass units are defined relative to it. This tool converts in real time between common units: milligram (mg), gram (g), kilogram (kg), tonne (t), ounce (oz), pound (lb) and stone (st). Useful for international recipes, shipping, gyms and packages. All calculations run locally in your browser, values are never sent anywhere.

How to use it

Enter the value in the field matching your unit (kg, lb, oz, etc.).
The other units update automatically in real time.
Use decimal comma or period, both work.
For very small or large numbers the result is shown in readable form (e.g. 1,500 g or 1.5 kg).
Everything runs locally, no data leaves your browser.

Examples

Body weight

Input75 kg

Output165.347 lb = 11.81 st = 2 645.5 oz

British scales typically show stone + pounds, "11 st 11 lb".

US recipe

Input8 oz

Output226.796 g

Rounded to 225 g in practice. "1 stick of butter" = 4 oz = 113 g.

Package shipping

Input2.5 lb

Output1 133.98 g ≈ 1.134 kg

Shipping brackets are usually in kg (0–1 kg, 1–2 kg, etc.). Always round up.

Common use cases

Converting recipes between American cup/oz and metric g/kg.
Checking shipping costs for packages with kg brackets.
Transferring body weight between kg and pounds/stone in gym apps.
Analytical lab values given in mg/L converted to g/L.
Estimating trailer capacity (kg) against American specs (lb).
Comparing nutrition per 100 g against per oz.

Frequently asked questions

Are "weight" and "mass" the same?: Not strictly in physics. Mass is a constant property of an object (measured in kg). Weight is the force acting on that mass due to gravity (measured in newtons). On Earth the numeric value is almost identical because g ≈ 9.81 m/s². In everyday use they are treated as synonyms.
What’s the difference between pound (avoirdupois) and troy pound?: Regular pound (lb, avoirdupois) = 453.592 g used for everyday weight. Troy pound = 373.242 g used only for precious metals and gems. A "troy ounce" (oz t) is also slightly heavier than a regular ounce: 31.103 g vs 28.349 g. The calculator uses avoirdupois unless specified otherwise.
What’s a "tonne" versus a "ton"?: Metric tonne (t) = 1,000 kg. The US uses "short ton" (2,000 lb ≈ 907.185 kg). The UK uses "long ton" (2,240 lb ≈ 1,016.047 kg). The calculator shows metric tonnes unless you pick the US variants.
How accurate is the conversion?: The calculator uses exact factors defined by BIPM: 1 lb = 0.453 592 37 kg (since 1959). Display precision is 6+ decimals for small values and rounds to a readable count for large values. Measurement device inaccuracy (bathroom scales, etc.) is usually larger than the conversion error.

Technical background

Conversion factors (BIPM 1959 standard): 1 lb = 0.453 592 37 kg (exact), 1 oz = 1/16 lb = 28.349 523 125 g, 1 stone = 14 lb = 6.350 293 18 kg, 1 short ton (US) = 2,000 lb = 907.184 74 kg, 1 long ton (UK) = 2,240 lb = 1,016.046 908 8 kg. Metric prefixes: 1 kg = 1,000 g = 1,000,000 mg. SI redefined the kilogram in 2019 based on Planck’s constant h = 6.626 070 15 × 10⁻³⁴ J·s, with no physical prototype. Previously "Le Grand K", a platinum-iridium cylinder at BIPM in Paris, was the physical reference.

Mass / Weight Reference Table