Article — Pounds to Grams Converter
Pounds to Grams: The Exact 453.59237 Factor and Where It Shows Up
One pound equals 453.59237 grams exactly. The factor is fixed by the 1959 International Yard and Pound Agreement, which defined the avoirdupois pound as precisely 0.45359237 kilograms. To convert pounds to grams, multiply by 453.59237. The reverse: grams × 0.00220462 = pounds. So 5 lb = 2,267.96 g, 100 g = 0.2205 lb, and 7 lb 4 oz = 3,289 g.
You meet this conversion in recipes (US vs. European cookbooks), at the post office (parcel limits in pounds or kilograms), in pediatrics (US birth weights in pounds, international standards in grams), and on shipping documents. The factor never changes, but the unit you start from often does.
The exact pounds-to-grams factor
1 lb × 453.59237 = 453.59237 g. The factor terminates — every decimal place after the 7 is zero. The reverse direction, grams to pounds, multiplies by 0.0022046226218487758..., a non-terminating decimal because 1 ÷ 453.59237 has no simple expression. For shop or kitchen use, 1 lb ≈ 454 g is accurate to 0.1% (off by 0.4 g per pound).
This is one of the cleanest conversions in the imperial system because the pound was redefined in 1959 to be exactly a fraction of the kilogram. Before that, the US pound, the imperial pound, and various trade pounds differed by small amounts — sometimes by 5–10 mg per pound. The 1959 treaty harmonized all of them under a single exact value.
The exact pound-to-kilogram value 0.45359237 was chosen because it preserved the existing US "pound" (defined in 1894 as 0.4535924277 kg) to 8 significant figures, while also matching the UK imperial pound to within 0.1 ppm. The 1959 treaty essentially rounded both definitions to 7 digits, then declared the result exact.
Pounds to grams in cooking and baking
US recipes use cups, ounces, and pounds. European recipes use grams and milliliters. Cross-pollination needs unit conversion. A US recipe calling for "1 pound of all-purpose flour" wants 454 g; "8 oz of butter" = 227 g; "1 lb 4 oz of ground beef" = 567 g. Volume-to-weight is the trickier direction because density varies (1 cup of flour = 120-125 g, but 1 cup of sugar = 200 g), so always convert weight first when possible.
For baking, weighing is more accurate than measuring by volume. A "cup of flour" can vary by 30 grams depending on how packed it is. Professional bakers and serious home bakers use a kitchen scale set to grams. The European convention of recipe-by-weight (every ingredient in grams) makes scaling easy: doubling a recipe is just doubling each gram figure, with no risk of measuring-cup ambiguity.
For mental math in the kitchen: pounds × 450 is close enough for most recipes. 1.5 lb × 450 = 675 g (true: 680.4 g). The error is under 1%, well inside the natural variation of ingredients. Use the exact 453.59 only when the recipe specifies a tight tolerance, such as bread hydration ratios.
Infant weight in pounds and grams
US hospitals record birth weight in pounds and ounces. International medical literature and World Health Organization growth charts use grams or kilograms. A 7 lb 4 oz baby is 3,289 g (about 3.29 kg). The formula: (lb × 453.59) + (oz × 28.35). Each ounce is 28.35 g, since 16 oz make a pound.
WHO defines low birth weight as <2,500 g (5 lb 8 oz). Very low birth weight is <1,500 g (3 lb 5 oz). Macrosomia — large for gestational age — starts above 4,000 g (8 lb 13 oz). Pediatricians track growth on percentile charts in grams; tracking on the same scale internationally makes literature comparison easier. For US parents reading a European baby book, this conversion comes up on every chart.
Shipping weight: pounds, ounces, and grams
USPS caps parcels at 70 lb (31.75 kg). Above that, the package goes to UPS Freight, FedEx Freight, or commercial trucking. Within that limit, US shippers price by both weight and dimension (dimensional weight). A 50-lb package (22.7 kg) is the airline economy class checked-bag limit; 70 lb (31.75 kg) is the premium-class checked-bag limit and the USPS Priority Mail ceiling.
European parcel carriers list weight limits in kilograms — typically 30 kg for standard service, with surcharges from 23 kg up. Crossing between US and European shippers means doing the conversion in advance: an exporter quoting "50 lb maximum" must communicate "22.7 kg maximum" to a European customer, or the customer may package to 22 kg (48.5 lb) and lose 2 lb of allowable capacity.
Avoirdupois pound vs. troy pound
The "pound" in this calculator is the avoirdupois pound — the standard commercial pound, 16 ounces, 453.59 g. Gold, silver, and other precious metals are traded by the troy pound, which contains only 12 troy ounces and totals 373.24 g. A pound of gold is therefore 18% lighter than a pound of flour. Confusing the two when calculating jewelry weights or bullion purchases is an expensive mistake.
Within the troy system, 1 troy ounce = 31.10 g, slightly heavier than the avoirdupois ounce of 28.35 g. So gold sold at "10 oz" means 311 g (10 troy oz), not 283.5 g. Spot price quotes on the London Bullion Market and the COMEX both use the troy ounce — every gold investor needs to remember that one ounce is not always one ounce.
The riddle "which weighs more, a pound of feathers or a pound of gold?" has a real answer: the feathers. Feathers are sold by the avoirdupois pound (453.59 g); gold by the troy pound (373.24 g). The pound of feathers weighs 80 g more than the pound of gold. Riddle has a literal answer because the word "pound" hides two different units.
The pound from Roman libra to 1959 treaty
The pound traces back to the Roman libra, a unit of weight standardized at about 329 g after 268 BC. The Latin word for the unit (and for the scales used to weigh it) gave us both the abbreviation "lb" and the £ symbol used for British currency — a pound of silver was the original "pound sterling." Roman commerce spread the libra across Europe and Britain.
Medieval England developed many local pounds. The merchant pound (7,200 grains, about 467 g), the tower pound (5,400 grains, 350 g), and the troy pound (5,760 grains, 373.24 g) coexisted for centuries. The avoirdupois pound (7,000 grains, 453.59 g) became the commercial standard around 1300 and was officially recognized by Henry VIII. The 1959 treaty fixed it permanently to the SI kilogram.
Why metric recipes use grams
Grams scale linearly with no units to switch — 50 g of butter is 50 g whether you have 50 g of butter or 5 kg. With pounds and ounces, doubling a recipe that calls for "1 lb 2 oz" gives "2 lb 4 oz," and a baker has to do the carry-over math (16 oz to a pound, not 10). Metric scales without that headache, which is the main reason European pastry has standardized on grams.
Bakers' percentages (weight of each ingredient as a percentage of flour weight) only work in metric. A bread formula at 65% hydration means 650 g of water to every 1,000 g of flour. The same recipe in pounds and ounces — "65% hydration to a 2 lb 3 oz flour weight" — requires mental gymnastics every time you scale. Grams just multiply.
1 lb 453.59 g1 oz 28.35 g1 lb 4 oz 567 g1 stone 6,350 g (14 lb)1 kg 2.2046 lb1 troy oz 31.10 g (gold)1 troy lb 373.24 gCommon pounds-to-grams mistakes
The biggest is mixing avoirdupois and troy pounds — they differ by 80 g per pound. Second is forgetting that ounces inside a pound-and-ounce reading need their own multiplier (28.35 g/oz), not 453.59 ÷ 10. Third is using "pounds" for fluid measure: a "pound" of liquid is not a thing in the US, and a UK "pint of beer weighs a pound" rhyme is only approximately true. Always confirm whether your "pound" is a unit of mass or a casualism for volume.
- 1 lb (avoirdupois) = 453.59237 g (exact)
- 1 oz (avoirdupois) = 28.3495 g
- 1 troy lb = 373.2417 g
- 1 troy oz = 31.1035 g
- 1 stone (UK) = 14 lb = 6,350 g
- 1 kg = 2.20462 lb
- USPS parcel cap = 70 lb = 31,751 g
- Low birth weight (WHO) = under 2,500 g (5 lb 8 oz)
- 454 g ≈ 1 lb (accurate to 0.1%)
- Mental math: double the lb count, add ~10% in hundreds of grams