How this instrument works
An avoirdupois ounce is one sixteenth of an avoirdupois pound, and both descend from something much smaller: a grain, fixed at exactly 64.79891 milligrams. A pound holds 7000 grains, so an ounce holds 437.5 of them — 28.349523125 g precisely. Merchants in medieval England used avoirdupois (avoir de pois, goods of weight) for wool, spices and bulk produce, and that trading system, not any laboratory, is where 16 came from.
Kilograms entered this arithmetic in 1959, when standards bodies in six countries — United States, United Kingdom, Canada, Australia, New Zealand and South Africa — agreed to define one pound as 0.45359237 kg. America had previously used 0.4535924277 kg, inherited from an 1893 order signed by Superintendent Thomas Mendenhall; Britain's figure diverged further down. Harmonising shifted commercial masses by roughly one part in ten million and ended decades of quiet disagreement between national copies.
Invert 0.028349523125 and you get 1600000000⁄45359237 ounces per kilogram, whose decimal expansion opens 35.27396194958… — so 35.2739619496, this sheet's factor, is that ratio rounded rather than measured. Ounces still run American retail: postage bands, cereal boxes, a 12 oz bag of coffee, boxing divisions, and birth weights read out as pounds and ounces in maternity wards on both sides of an ocean. Kilograms do almost everything else, and since 20 May 2019 have been pinned to a fixed Planck constant. Because both units now sit on definitions rather than artefacts, converting between them is pure arithmetic: nothing depends on gravity, altitude or which balance you own.
- Type your mass into the Kilograms (kg) field — 1 kg is preloaded, and a step of 0.001 lets you key grams straight in.
- Weighing 500 g? Enter 0.5 rather than 500; this field reads kilograms only.
- Read Ounces (oz) directly beneath, recomputed on every keystroke.
- Want pounds and ounces? Divide that result by 16 — whole part gives pounds, remainder times 16 gives leftover ounces.
- Working backwards from an ounce figure, divide by 35.2739619496 to recover kilograms.
Worked example — one kilogram on an American scale
A British recipe asks for 1 kg of strong bread flour and your kitchen scale reads ounces only. Enter 1 in Kilograms (kg); Ounces (oz) returns 35.2739619496. Call it 35.27 oz, or divide by 16 and keep a remainder to get 2 lb 3.27 oz, which is how an American baker would actually weigh it out.
Rounding matters more than such a small number suggests. A pub shortcut of 2.2 lb per kilogram yields 35.2 oz — about 0.21% light, worth two grams of flour here, but two kilograms adrift on a tonne of palletised freight. Carrying all ten decimals costs nothing and keeps a shipping manifest agreeing with its own totals.
Questions
Is one kilogram exactly 35.2739619496 ounces?
No — that figure is rounded. Exactness runs in reverse: one avoirdupois ounce is precisely 0.028349523125 kg, being a sixteenth of a pound defined as 0.45359237 kg. Inverting yields 1600000000⁄45359237 oz per kilogram, a non-terminating decimal opening 35.27396194958…. Stopping at ten decimals leaves relative error under one part per trillion, which no commercial balance on earth could detect.
Is a troy ounce the same ounce?
No, and mixing them up gets expensive. A troy ounce, used for gold, silver and platinum, weighs 31.1034768 g — roughly 10% more than an avoirdupois ounce at 28.349523125 g. Troy weight also counts 12 ounces to its pound rather than 16, so a troy pound is lighter even though its ounce is heavier. This sheet handles avoirdupois only; never price bullion with it.
Do imperial and US customary ounces differ?
For mass, no. Since 1959 both systems share one international avoirdupois ounce of 28.349523125 g, so a British ounce of butter and an American ounce of butter weigh identically. Volume is where they part company: a US fluid ounce holds 29.5735295625 mL against an imperial 28.4130625 mL, a 4% gap that quietly ruins cocktail ratios. Fluid ounces measure space, not mass, and belong to a different converter.
How do I express my answer as pounds and ounces?
Divide by 16, then split. A 3.5 kg newborn converts to 123.4588668 oz; 123.4588668 ÷ 16 = 7.7162, giving 7 lb, and 0.7162 × 16 = 11.46 oz — recorded as 7 lb 11½ oz on a maternity chart. Hold full precision until that final step, since rounding twice can move a birth weight by a whole ounce.
Why does the 2.2 pounds shortcut fall short?
Because one kilogram is 2.20462262185 lb, and lopping it to 2.2 discards everything past two decimals. Multiply by 16 and that loss becomes visible: 2.2 lb shows as 35.2 oz against the true 35.2739619496 oz, about 0.21% low. Fine for one bag of apples, poor across 500 kg of palletised stock, where it hides over one kilogram of product.
Did the 2019 SI redefinition change any of these numbers?
Numerically nothing changed. On 20 May 2019 the kilogram stopped being the platinum-iridium cylinder held near Paris since 1889 and became instead one consequence of fixing Planck's constant at 6.62607015 × 10⁻³⁴ J s. That value was chosen for continuity, so 0.45359237 kg per pound still stands, every ounce keeps its old weight, and not one shop scale required recalibration.