Weight Converter Online Free

How to Convert Weight

1. 1Select the source unit from the From dropdown — e.g. kilograms.
2. 2Enter your value. The target unit result updates instantly. Use the swap button to reverse direction.
3. 3The all conversions table shows the value in every supported unit simultaneously — useful for checking multiple units at once.

Metric and Imperial Weight Units

The metric system scales by powers of 10: 1000 mg = 1 g, 1000 g = 1 kg, 1000 kg = 1 metric ton. Imperial units use less regular ratios: 16 oz = 1 lb, 14 lb = 1 stone, 2000 lb = 1 US ton. The exact bridge between the systems is 1 lb = 0.45359237 kg, defined by international agreement in 1959.

That oddly precise number is not an approximation — it is a definition. Since 1959 the international avoirdupois pound has been fixed at exactly 0.45359237 kilograms by agreement among the English-speaking countries, which means every pound-to-kilogram conversion is exact rather than measured. The everyday shortcut of “multiply kg by 2.2” comes from the reciprocal (1 kg ≈ 2.20462 lb), and it is close enough for luggage and body weight but drifts noticeably on large quantities, which is why this converter uses the full factor.

Avoirdupois vs Troy: Not All Ounces Are Equal

One conversion trap is worth knowing about because it causes real confusion: the ounceis not a single unit. The everyday ounce used for food, mail, and body weight is the avoirdupois ounce, equal to about 28.35 grams, and it is what this converter uses. Precious metals like gold and silver, however, are traditionally weighed in troy ounces, which are heavier at about 31.10 grams — so a “one-ounce” gold coin is meaningfully heavier than a one-ounce chocolate bar. There are also confusingly fewer troy ounces in a troy pound (12 rather than 16). If you are converting the weight of jewellery or bullion, make sure you are working in troy units; for everything else, the standard avoirdupois ounce here is correct.

The Conversions People Actually Need

In practice a handful of conversions cover most real use. Body weight moves between kilograms, pounds, and (in the UK and Ireland) stone, where one stone is 14 pounds or about 6.35 kg. Cooking and baking often means turning a US recipe's ounces into grams — roughly 28 grams per ounce — which a kitchen scale makes far more reliable than volume cups. Shipping and luggage hinge on the kg↔lb bridge, where the difference between the 2.2 shortcut and the exact factor can decide whether a bag is over an airline's limit. And science and industry lean on the clean metric ladder — milligrams to grams to kilograms to tonnes, each a factor of a thousand apart. Because this tool shows every unit at once and uses exact factors, you can move between any of these without memorising a single number.

Worked Example: The Airline Baggage Limit Rounding Trap

Most international economy checked-bag allowances are listed as 23 kg — which airlines almost universally describe as "50 lb" on English-language signage. Converted precisely, 23 kg × 2.20462 = 50.71 lb, which is actually over 50 lb. Airlines round down in their marketing but weigh bags in kilograms at the counter, so a bag that reads "50.5 lb" on a US bathroom scale is still under the real 23 kg limit — it is the kg figure that determines the fee, not the rounded lb figure quoted in travel guides.

The gap matters most near the threshold: a bag at 23.3 kg (51.4 lb) is over the limit by 300 g, small enough that shifting one paperback book to a carry-on avoids an overweight fee that commonly runs $75–$200 per bag.