Weight conversion calculators

How to choose and check a conversion

Mass units describe the amount of matter, although everyday language commonly calls these “weight” units. Kilograms and grams are metric units; ounces, pounds, stones, short tons, and long tons are used in customary or imperial contexts. A metric tonne equals exactly 1,000 kilograms.

Check which ton a source means before converting. A U.S. short ton, British long ton, and metric tonne are different quantities. Product labels and shipping documents usually specify the convention. If they do not, ask rather than guessing.

For cooking, shipping, and fitness, use a scale suited to the required precision. Converting a rounded measurement cannot restore detail that the original scale did not capture. Keep the unrounded value during arithmetic and round only the final result.

Accuracy and sources

Convertly keeps additional precision during calculation and rounds the display for readability. Match the final precision to the source measurement and the purpose of the answer. See our methodology and source policy for definitions, primary references, limitations, and correction procedures.

Exact definitions, estimates, and rounding

Some unit relationships are exact definitions, while a measured input is still limited by the instrument used to obtain it. A calculator can correctly apply an exact factor without making the original measurement more precise. Keep the original unrounded value, perform the conversion, and round the final result to a level appropriate for the task.

Use the stated formula to check the direction of the conversion. When possible, test a familiar value such as 1, 10, or 100 before relying on an unfamiliar result. For professional, regulated, health, safety, or contractual work, confirm the required convention and rounding rule in the controlling standard or document.