Avoirdupois is the formal name for the pounds and ounces on every grocery label, postal scale and bathroom scale in the United States, and for the stone that still describes body weight in Britain and Ireland. The system has a dozen units, several of which mean different amounts on either side of the Atlantic. This converter handles all of them and adds the mixed “pounds and ounces” and “stone and pounds” forms that people actually use.
How to use the avoirdupois weight converter
- Enter the weight in Value.
- Pick its unit in From: grain, dram, ounce, pound, stone, quarter, hundredweight, ton, or a metric unit.
- Pick the unit you want in To.
- Read the result plus three breakdowns on the tape: pounds and ounces, stone and pounds, and ounces and drams. The table lists all 13 units.
Avoirdupois conversion formula
All units are exact multiples of the pound, and the pound is exactly 0.45359237 kg under the 1959 international agreement. A conversion is therefore:
To split a decimal into pounds and ounces, keep the whole pounds and multiply the fractional part by 16:
Worked example: ounces to pounds and ounces
A recipe calls for 44 oz of tomatoes, and the store sells them by the pound:
44 oz ÷ 16 = 2.75 lb
Whole pounds: 2. Remaining: 0.75 × 16 = 12 oz, so 44 oz = 2 lb 12 oz.
In metric: 2.75 × 0.45359237 = 1.2474 kg.
A newborn’s weight works the other way. A baby weighing 7 lb 6 oz is 7 + 6/16 = 7.375 lb, and 7.375 × 453.59237 g = 3,345 g.
The avoirdupois units
| Unit | Definition | Grains | Grams |
|---|---|---|---|
| grain (gr) | base unit | 1 | 0.06479891 |
| dram (dr) | 1/16 oz | 27.34375 | 1.7718452 |
| ounce (oz) | 1/16 lb | 437.5 | 28.349523 |
| pound (lb) | 16 oz | 7,000 | 453.59237 |
| stone (st) | 14 lb | 98,000 | 6,350.29 |
| quarter (UK) | 28 lb | 196,000 | 12,700.59 |
| short hundredweight (US) | 100 lb | 700,000 | 45,359.24 |
| long hundredweight (UK) | 112 lb | 784,000 | 50,802.35 |
| short ton (US) | 2,000 lb | 14,000,000 | 907,184.74 |
| long ton (UK) | 2,240 lb | 15,680,000 | 1,016,046.91 |
US and British differences
Both countries share the grain, dram, ounce and pound, so a pound of butter weighs the same in Boston and Bristol. They split at the larger units:
- Stone and quarter. Britain kept the 14-pound stone and the 28-pound quarter. They have no legal use in the United States, though Americans recognize the stone from British TV and sports.
- Hundredweight. US cwt = 100 lb; UK cwt = 112 lb. Livestock and grain prices in the US are often quoted “per cwt,” meaning per 100 pounds.
- Ton. US short ton = 2,000 lb; UK long ton = 2,240 lb. The 12% difference matters on freight bills and in shipping tonnage.
Avoirdupois versus troy
Precious metals are weighed in the separate troy system. The grain is identical, but a troy ounce is 480 grains instead of 437.5, so it is about 9.7% heavier than the ounce described here. A troy pound, with only 12 ounces, is lighter than an avoirdupois pound. If you are weighing gold, silver or platinum, use the troy weight converter. For metric-heavy work, the general weight converter covers micrograms through tonnes, and stone to kilograms gives a quick body-weight chart.
A note on drams
The avoirdupois dram (1.77 g) is different from the apothecaries’ dram (3.89 g) and the fluid dram (3.70 mL). Today the avoirdupois dram survives mainly on shotgun shell boxes, where “dram equivalent” compares a modern load with an old black-powder charge measured in drams.
Frequently asked questions
What does avoirdupois mean?
It comes from the Anglo-Norman French phrase for "goods of weight" and names the system of pounds and ounces used for ordinary merchandise. When a US or UK label says ounces or pounds without qualification, it means avoirdupois units.
How many ounces are in a pound?
There are 16 avoirdupois ounces in an avoirdupois pound. Each ounce is exactly 28.349523125 g, and the pound is exactly 453.59237 g.
Why is a British hundredweight 112 pounds?
In the British system a hundredweight is 8 stone of 14 lb, which is 112 lb. The United States dropped the stone and kept a round 100-pound hundredweight, which is why US and UK tons (20 hundredweights each) are 2,000 lb and 2,240 lb.
How many grains are in a pound?
Exactly 7,000. The grain (64.79891 mg) is the one unit shared by the avoirdupois, troy and old apothecaries' systems, which makes it a convenient bridge between them.