Weight Converter

How weight conversion actually works

Converting between weight units is, under the hood, a single idea: pick one base unit, express every other unit as a multiple of it, and convert by going through that base. This tool uses the gram as its base. When you type a value into any field, it multiplies your number by that unit's gram factor to get a base value in grams, then divides that base value by every other unit's factor to fill in the rest. Every box updates live because they all derive from one shared number. The factors are exact constants — for example, one pound is defined as exactly 453.59237 grams, and one ounce as exactly 28.349523125 grams — so the math is precise, not approximate.

The units and their exact factors

A worked example

Say you type 150 into the Pounds field. The tool computes the base value as 150 × 453.59237 = 68,038.8555 grams. To show kilograms it divides by 1,000, giving 68.0388555 kg. To show stones it divides 68,038.8555 by 6,350.29318, giving about 10.714 st. To show ounces it divides by 28.349523125, giving 2,400 oz exactly (since a pound is exactly 16 ounces). Every field is computed from that same 68,038.8555-gram base, which is why nothing ever drifts out of sync.

The tool also formats results sensibly: very large or very small numbers switch to scientific notation, values above 1,000 are shown to 10 significant figures, and smaller values to 8, so you never see a misleading wall of floating-point noise like 67.99999999998.

The "real-world comparisons" feature

Beyond raw numbers, the tool adds intuitive comparisons so a weight means something. Enter a few thousand kilograms and it might say "≈ 1.4 average cars (~1,400 kg each)"; enter a couple of grams and it offers "≈ 2.0 paperclips (~1 g each)." These anchors are deliberately rough and clearly labelled with their assumed reference weight — an African elephant at 5,000 kg, an adult at 70 kg, an apple at 182 g — so you can sanity-check a result against everyday intuition.

Common pitfalls this tool helps you avoid

• Pounds-mass versus pounds-force. This converter handles mass. The pound here is the unit you weigh groceries in, not a measure of force. Do not use it for engineering force calculations without accounting for gravity.
• Short ton vs long ton vs tonne. These three are commonly confused. A metric tonne is 1,000 kg, a US short ton is 907.18 kg (2,000 lb), and an imperial long ton is 1,016.05 kg (2,240 lb). Using the wrong one introduces a 10% error — the tool keeps all three separate on purpose.
• Ounces of weight vs fluid ounces. The ounce here is a unit of mass (1/16 of a pound). It is unrelated to the fluid ounce, which measures volume.
• Stones and pounds together. Body weight in the UK is often quoted as "11 st 4 lb," which is 11 stones plus 4 pounds, not 11.4 stones. Convert each part and add, or enter the total in pounds (158 lb in that example).

Where this is useful

Recipes that mix grams and ounces, shipping where carriers price by the kilogram while your scale reads pounds, fitness tracking across metric and imperial regions, lab work converting milligrams to grams, and freight planning where short tons and tonnes appear side by side. Because every unit derives from the same exact gram constants and all calculation happens in your browser, the conversions are both accurate and private — nothing you type is sent anywhere.