The avoirdupois system is the everyday weight system used across the English-speaking world, but it hides more units than most people realize, and several of them, hundredweight and ton especially, mean different things in the US versus the UK. This calculator converts between all 10 avoirdupois units instantly, showing every conversion at once so you never have to guess which “ton” a figure is actually using.
Rather than converting between just two units at a time, this calculator takes your input and instantly shows it expressed in all 10 avoirdupois units at once: Grains, Drams, Ounces, Pounds, Stone, UK Quarters, US and UK Hundredweight, and US and UK Tons. This is especially useful for this particular unit family, since several of these units are easy to confuse, and having every conversion visible at once avoids picking the wrong one silently.
Everything in this system ultimately reduces to a fixed number of pounds, which is what this calculator uses as its internal reference point when converting between any two units.
| Unit | US (short) | UK (long) |
|---|---|---|
| Hundredweight | 100 lb | 112 lb |
| Ton | 2,000 lb | 2,240 lb |
This split exists because the historical UK hundredweight was defined as 8 stone (8 × 14 lb = 112 lb), while the US version was simplified to a flat 100 lb for easier arithmetic, and the respective “ton” figures scale up from each. This is exactly why this calculator lists US and UK versions of both units separately rather than assuming one definition, using the wrong one when converting a shipping weight, a historical recipe, or an old engineering spec can throw off a result by more than 10%.
Grains and drams sit at the small end of the avoirdupois scale and are less commonly encountered day to day, grains occasionally show up in ammunition and archery (bullet and arrow weights are often specified in grains), while drams appear in some older pharmacy and cooking contexts. Both convert cleanly through the same pound-based reference: 7,000 grains or 256 drams per pound.
Stone (14 lb) is still commonly used for body weight in the UK and Ireland, even though it isn’t part of the US customary system at all. This calculator handles it the same way as every other unit, converting it cleanly against grains, ounces, pounds, or any other supported unit.
The US (short) versions use round numbers, 100 lb per hundredweight and 2,000 lb per ton, while the UK (long) versions are based on the historical hundredweight of 112 lb (8 stone), scaling up to a 2,240 lb ton. Using the wrong regional definition can meaningfully change a converted result, which is why this calculator lists both separately.
Grains are still commonly used to specify ammunition bullet weight and archery arrow weight, both contexts where the small unit size gives more precise specification than ounces or pounds would.
No, stone (14 lb) is specific to UK and Irish usage, mainly for body weight. It isn’t part of the US customary weight system, though this calculator converts it the same way as any other avoirdupois unit since it still fits the same underlying pound-based structure.