How this instrument works
Ounces and pounds here are avoirdupois units, brought into English trade from medieval France, where aveir de peis meant goods of weight. An avoirdupois pound holds 7000 grains and splits into sixteen ounces of 437.5 grains each. That sixteen rewards scrutiny: ounce descends from Latin uncia, meaning one twelfth, because Rome divided its libra into twelve parts; lb still points back to libra, though only troy weight kept Rome's twelve.
Sixteen is a power of two, which is why this particular factor behaves so well. Halve one pound and you have 8 oz; halve again for 4 oz, then 2, then 1 — precisely what balance beams and nested weights can do, precisely why butchers, grocers and coffee roasters settled on quarter-pound and half-pound quantities. It also means 1/16 terminates after four decimal places as 0.0625, which is dyadic, so binary floating point stores it perfectly. Very few cross-system conversions can claim as much.
Both units now rest on an SI foundation. Since the 1959 international yard and pound agreement, an avoirdupois pound is exactly 0.45359237 kilograms, which makes one ounce exactly 28.349523125 grams — definitions chained end to end, carrying no measurement uncertainty at any link. Americans meet these units at postal counters, deli scales and nutrition panels; British and Irish cooks meet them in older recipes; boxing and wrestling still make weight in them; and maternity wards on both sides of the Atlantic announce newborns as, say, 7 lb 9 oz.
- Type your weight into the Ounces (oz) field — it opens at 24 oz, so a result is on screen before you touch anything.
- Read your answer on the Pounds (lb) line. It recalculates on every keystroke; there is nothing to submit.
- Fractional ounces are welcome. The field steps in thousandths, which suits a digital kitchen or postal scale.
- Want pounds-and-ounces instead of a decimal? Keep the whole pounds, then multiply whatever is left over by 16.
- Going the other direction, from pounds back to ounces, multiply your pound figure by 16 rather than by 0.0625.
Worked example — a 24 oz parcel at the counter
A shop drops a padded envelope onto a postal scale and reads 24 ounces. Enter 24 into the Ounces (oz) field and the Pounds (lb) line returns 1.5, because 24 × 0.0625 = 1.5 — or, said without decimals, 24 ÷ 16 is one and a half pounds.
Written onto a shipping label that becomes 1 lb 8 oz: one whole pound, with a leftover 0.5 lb multiplied by 16 to give 8 oz. Carriers who price by weight will round a 1.5 lb parcel up to a 2 lb billing tier, so the half matters commercially even though the arithmetic itself is exact.
Questions
Is 0.0625 an exact factor or a rounded one?
Exact. It is simply 1/16 written as a decimal, and 1/16 terminates cleanly because 16 is a power of two. Sixteen avoirdupois ounces make one avoirdupois pound by definition, so nothing is approximated anywhere along the way — not in that factor, and not in how a machine stores it, since 0.0625 is representable in binary floating point without any error.
Is a troy ounce the same as an ounce here?
No, and confusing them gets expensive. A troy ounce is 31.1034768 g against 28.349523125 g for an avoirdupois ounce — roughly 10% heavier — and only twelve troy ounces make a troy pound. Gold, silver and platinum trade in troy ounces; groceries, parcels and people are weighed in avoirdupois ounces. Use this converter for avoirdupois only.
Does a fluid ounce convert with this same factor?
No. A fluid ounce measures volume, not mass, so no fixed conversion to pounds exists without knowing what fills the container. As a rough anchor, a US fluid ounce of cool water weighs about 1.04 avoirdupois ounces, which is why a US pint of water comes to a little over a pound. Anything denser or lighter than water breaks that near-coincidence immediately.
Do British and American ounces differ?
Not for weight. Both countries signed that 1959 international yard and pound agreement, so an avoirdupois ounce is 28.349523125 g on either side of the Atlantic, and sixteen make a pound in each. Fluid ounces are where imperial and US customary genuinely diverge: an imperial fluid ounce is about 28.41 mL, a US fluid ounce about 29.57 mL.
How do I turn 1.5 lb into pounds and ounces?
Keep whole numbers as pounds and multiply what remains by 16. So 1.5 lb is 1 lb plus 0.5 × 16 = 8 oz, written 1 lb 8 oz. A frequent slip is reading a decimal as though it were ounces and writing 1 lb 5 oz, which comes out three ounces light. Decimal pounds and pound-and-ounce notation agree only at whole pounds.
Why not divide by 12, as older measures did?
Because avoirdupois weight never used twelve. Twelve to a pound belongs to troy weight, inherited from Rome's libra, and it survives in precious metals and in our word ounce itself, from uncia. Trade goods in England went to a sixteen-ounce pound and stayed there. Dividing 24 oz by 12 gives 2 lb rather than 1.5 lb — a third too heavy.