Convert lb to g

A pound is exactly 0.45359237 kilograms by the same 1959 agreement that fixed the inch. The abbreviation "lb" comes from libra, the Roman unit it descends from.

Grams are the unit of recipes and postage outside the United States, and the unit nutrition labels use nearly everywhere.

The factor is 453.59237, and almost nobody carries that around. Rounded to 450 it is off by 0.79 % — which stays invisible on small numbers and turns into a whole unit somewhere around 1,000 lb.

That is the number worth knowing before you round: not the error itself, but where it stops being ignorable. Below that point the shorter factor is the sensible one; above it, use the field above, which never rounds until it prints.

The pound has been defined in metric terms since the international yard and pound agreement of 1959, and in this page's units that comes out at 453.59237 g to one. The definition is exact by stipulation — it was not measured, and it cannot be refined by measuring it better. The decimal above is the whole of it, with nothing rounded away at the end.

Before that agreement the US and the British versions differed slightly, and old survey figures still carry the older definition. For anything outside land surveying the difference is far below the precision anybody is working to.

A German Pfund, a French livre and a Dutch pond all mean exactly 500 g. They are not the pound this page converts and they never were — after metrication the old name was kept for a convenient half-kilogram, and it stayed in domestic use for exactly the things recipes are made of: flour, butter, sugar, mince, fruit. A recipe asking for ein Pfund Mehl wants 500 g of flour.

The gap is 10.2 per cent, and its effect depends entirely on whether it is applied evenly. A whole recipe converted at 453.6 instead of 500 makes a smaller version of the same dish and mostly works. A recipe where the flour came from a Pfund and the water from a millilitre figure is a different recipe: the ratio has moved by a tenth, which in bread or pastry is the difference between a dough that behaves and one that does not.

When a US recipe says a pound, it is generally naming something you buy rather than something you measure. A pound of butter is four sticks; a pound of pasta is the standard box; a pound of ground beef is the tray; a pound of powdered sugar is the bag. The instruction is "use the whole packet", and the weight is incidental.

That matters when converting, because the metric equivalent is a different packet. European butter comes in 250 g blocks, so a pound is 453.6 g and two blocks are 500 g — a bare ten per cent more, which is fine in a cake batter and not fine in a pastry where the fat-to-flour ratio is the recipe. Where a pound is clearly a package, the honest conversion is often to the nearest local package rather than to the nearest gram.

The three roundings differ by less than a per cent and they are not interchangeable in every context. 450 g is 0.8 per cent light, 454 g is 0.09 per cent heavy, and 453.6 g is as close as a domestic scale reading to the gram can get. For anything simmered, braised or roasted, any of the three disappears into the cooking.

The place to care is where a small ingredient is measured against a large one. Scale a bread recipe to five pounds of flour at 450 g and you have 2,250 g rather than 2,268 — eighteen grams short — while the salt and yeast, being quoted in grams already, do not shrink with it. The result is a slightly saltier, faster dough. Either round every ingredient by the same proportion, or round none of them.

Bread recipes are ratios expressed against the flour: the flour is 100 per cent and everything else is a share of it. That structure makes converting from pounds trivially safe, because only one number has to be converted. One pound of flour is 453.59 g; at 65 per cent hydration the water is 294.8 g, at 2 per cent the salt is 9.1 g, and none of those figures came from a conversion.

It also makes the 500-gram pound harmless, provided the whole recipe uses it. A Pfund of flour is 500 g, the same percentages give 325 g of water and 10 g of salt, and the loaf is the same loaf ten per cent larger. The ratio is the recipe; the absolute quantities are the batch size, and this conversion only ever changes the second.

American quantities arrive as compounds — 1 lb 2 oz, 2 lb 4 oz — and the safe route to grams is through ounces rather than through two separate conversions. 1 lb 2 oz is 18 oz, and 18 × 28.349523125 is 510.3 g. Converting the pound to 453.6 and the ounces to 56.7 and adding gives the same answer and gives it twice as many chances to go wrong.

The reverse trap is a decimal that looks like a compound. A quantity written as 1.2 lb is 544.3 g, while 1 lb 2 oz is 510.3 g — a difference of 34 g hiding behind two characters. Where a recipe has been retyped or scraped, that ambiguity is worth resolving from the context before it is converted; a quantity that is a multiple of a quarter pound is almost certainly a compound.

British bread tins are sold as 1 lb and 2 lb, and the number describes the finished loaf the tin is meant to produce rather than any quantity you would weigh into it. A 2 lb tin does not take 907 g of dough; it takes rather less, because the loaf rises above the rim and loses water in the oven.

The same applies to a good deal of cookware nomenclature and to a fair number of recipe titles. A pound cake takes its name from a historic recipe of a pound each of flour, butter, sugar and eggs, which is a ratio and a description rather than an instruction to weigh 453.6 g of four things. Convert quantities; leave names alone.

The reliable method with a recipe in pounds is to rewrite the whole ingredient list in grams before touching a pan. Doing it line by line while cooking means converting under time pressure, at inconsistent precision, and with the scale in whatever mode the last ingredient left it in — which is how a quarter pound becomes a quarter kilogram.

Writing it out also surfaces the sanity check. A converted list should total to something plausible for the number of servings claimed, and the ingredient proportions should look like the dish they are supposed to be. A single conversion error stands out badly against the other lines; the same error met alone, mid-recipe, does not stand out at all.