Unit Converter Factor Sources: The Exact Numbers Behind Every Conversion

Every unit converter is a table of constants wearing a user interface. We pulled the

table out of our own unit converter and checked each factor against its reference

definition. The audit found factors that are exact by definition, factors truncated at

roughly one part per million, one mislabeled speed unit, and a gap between what the

marketing copy claims and what the code ships.

What the converter actually ships

The component defines 5 categories and 26 units: 7 length, 6 weight, 3 temperature, 6

area, and 4 speed. Our SEO copy for the page promises 50 or more units across 8

categories including volume, data size, and time. The component contains none of those

three categories. Trust the 26, and treat the page copy as stale until it is fixed.

Every conversion passes through one base unit

Each unit defines two functions, one that converts a value into the category base and

one that converts back. The bases are metre, kilogram, Celsius, square metre, and metre

per second. A conversion chains the two: source to base, then base to target.

This design has one measurable consequence. A direct inch to mile factor would be a

single division, while the chained path computes 0.0254 divided by 1609.344. The tool

shows the result of the chained arithmetic, and very small results trigger the

exponential display branch: 1 inch converts to 1.5783e-5 miles, because the formatter

switches to exponential notation below 0.0001.

The factor table as shipped

The length and speed factors carry over cleanly because the international definitions

of the inch, foot, mile, and mile per hour are terminating decimals. The definitions of

the pound, ounce, acre, and knot are not, so the code stores rounded versions.

What one part per million looks like on screen

The pound is defined as 0.45359237 kg. The code stores 0.453592, which is 0.82 parts

per million low. Convert 1 lb to kg in the tool and it displays 0.453592, dropping the

37 in the seventh and eighth digits. The ounce factor at 0.0283495 sits 0.82 ppm under

its 0.028349523125 definition. The acre factor 4046.86 sits 0.88 ppm under 4046.8564224

square metres, a gap of about 0.0036 square metres per acre. The knot factor 0.514444

sits 0.86 ppm under 1852 divided by 3600.

For cooking, travel, and shopping these errors are invisible. For land surveys and

trade documentation they are not, and you should pull definitions rather than tools

for those uses.

The display rule that rounds everything you see

Results pass through one formatter before display. Values at or above 1e9, and nonzero

values below 0.0001, print in exponential notation with 4 decimal places. Everything

else prints with 8 significant digits, with trailing zeros stripped. Two consequences

follow. The truncation errors above live in the seventh significant digit, at the edge

of what the display even shows. And any conversion you read from the tool carries at

most 8 significant digits regardless of what you typed, so the tool cannot settle a

dispute at the ninth digit.

Temperature is the one category with affine conversions rather than multiplicative

factors, and the formulas are the standard ones. The two scales cross at minus 40,

which you can verify in the tool: minus 40 Fahrenheit converts to minus 40 Celsius.

Two label defects the audit found

The speed category contains an entry labeled km/s whose factor divides by 3.6. That

factor converts kilometres per hour to metres per second. A true km/s entry would

multiply by 1000. Convert 1 m/s with that entry and the tool returns 3.6, which is the

km per hour value. The arithmetic is correct for km/h, and only the label is wrong, so

read that dropdown as km/h until it is fixed.

The second defect is cosmetic and stranger: the unit labels are Turkish in every

language. An English visitor sees Santimetre, Mil, Ons, Dönüm, and Hektar in the

dropdowns, because the labels are hardcoded rather than localized. Dönüm labels the

international acre, 4046.86 square metres, which will also confuse Turkish readers,

since a dönüm is traditionally a different area.

Checklist before you cite a conversion

• You confirmed the category, because the tool resets source and target to the first

two units whenever you switch.

• You read the km/s entry as km per hour.
• You accept 8 significant digits as the ceiling of the output.
• You treat pound, ounce, acre, and knot results as carrying roughly 1 ppm of factor

error.

• You use reference definitions, not any converter, for surveying and trade figures.

The default state is 1 metre to feet, which displays 3.2808399 and gives you a one

keystroke sanity check that the tool is alive.

Recompute one factor with your own definition. Open the

[unit converter](https://webrecast.com/en/unit-converter), convert 1 pound to

kilograms, and compare the seventh digit against 0.45359237. If your screen shows

anything other than 0.453592, the table above is out of date and the code has moved

on, which is exactly the kind of report that keeps this audit honest.