Methodology

Every conversion on this site derives from three exact constants and two arithmetic operations. Nothing is estimated, approximated or looked up from a table, and the same constants are used on every page.

The constants

Three definitions produce every figure on this site. Each is exact by international agreement rather than measured, so none carries an uncertainty:

One international avoirdupois pound is exactly 453.59237 grams, fixed by the International Yard and Pound Agreement of 1959. One avoirdupois ounce is exactly 28.349523125 grams, being one sixteenth of that pound. One troy ounce is exactly 31.1034768 grams and is used only for precious metals; twelve troy ounces make a troy pound of 373.2417216 grams, which is lighter than an ordinary pound.

These three values are declared once, in a single file, and every page imports them. No conversion number is written a second time anywhere on the site, which removes the possibility of two pages disagreeing.

The formulas

Each conversion is a single division or multiplication against one of the three constants. The complete set is:

The pounds-and-ounces breakdown takes the whole number of pounds first, then multiplies the leftover decimal by 16 because one pound contains 16 ounces. Where rounding pushes the ounces to a full 16, one pound is added and the ounces reset to zero, so the display never reads something impossible such as 2 lb 16 oz.

The rounding rule

Values are rounded half away from zero at the precision you select. Because the converter accepts only values of zero or more, this is the same as rounding half up: a digit sequence ending in exactly 5 rounds upward. You can choose 2, 4 or 6 decimal places, and the underlying calculation always runs at full precision with rounding applied only at the moment of display.

Rounding is the reason two converters can disagree in the fourth decimal place while both being correct. 1,000 grams equals 2.2046 pounds at four decimals and 2.204623 pounds at six; the difference of 0.000023 pounds is roughly 10 milligrams. For everyday weighing two decimals is sufficient. Six is worth using for precious metals, laboratory work, or any situation where the figure will be multiplied by a large quantity.

How the calculations are tested

Every conversion function is covered by an automated test suite that runs in the browser. The suite checks each function against independently known values, including 1,000 g = 2.20462262 lb, 453.59237 g = 1 lb exactly, 100 g = 3.5274 oz and 31.1034768 g = 1 troy oz, and it also verifies the behaviour for empty input, negative numbers, zero, non-numeric text and very large numbers.

The tests are public. Opening /test.html on this site runs them live and prints a pass or fail line for every case, so the arithmetic behind the converter can be verified without taking anything here on trust.

Where the calculation runs

All arithmetic runs in your own browser. No weight you type is transmitted, logged or stored on a server, because there is no server-side calculation of any kind. The converter continues to work with no network connection once the page has loaded.

Primary sources

If you find a figure on this site that disagrees with any of those sources, please report it and it will be corrected.