Unit converter

Convert length, weight and temperature units.

Type

An overseas listing gives the dimensions in inches and the shipping weight in pounds, and neither number means anything to you until you translate it. Weather forecasts are the same problem in reverse — 78°F could be pleasant or uncomfortable depending on which scale you grew up with.

This converter covers three families of units: length, weight and temperature. Choose the category, type a value, pick the two units, and the answer appears as you type.

How it works

The three fields

Type — Length, Weight or Temperature. Changing this rebuilds the unit dropdowns below it, so pick the category first.
Value — the number you want converted.
From / To — the two unit dropdowns. The result updates on every change; there is no submit button.

Length and weight go through a base unit

Rather than storing a conversion factor for every possible pair, the tool converts your input into one base unit — metres for length, kilograms for weight — and then divides that into the target unit. One base per category keeps the arithmetic to a single multiply and a single divide, so error never compounds across a chain of steps.

Unit	Value in base unit
1 inch	0.0254 m (exact)
1 foot	0.3048 m (= 12 inches)
1 yard	0.9144 m (= 3 feet)
1 mile	1,609.344 m
1 pound	0.45359237 kg (exact)
1 ounce	about 0.02835 kg (= 1/16 pound)
1 geun	0.6 kg

The inch and pound figures are not approximations. The 1959 international yard and pound agreement fixed them at exactly those metric values, which is why the decimals simply stop where they do.

Temperature needs offsets, not just factors

Length and weight scales all start at zero in the same place, so a single multiplier is enough. Temperature scales do not — 0°C and 0°F describe different physical conditions — so the tool applies these formulas instead:

Celsius to Fahrenheit: °F = °C x 9/5 + 32
Fahrenheit to Celsius: °C = (°F - 32) x 5/9
Celsius to Kelvin: K = °C + 273.15

Feeding in 78°F returns roughly 25.6°C — short-sleeve weather.

One caveat on precision

Results are rounded to six decimal places for readability. That is far beyond everyday needs, but for machining tolerances or lab reports, work from the exact factors in the table above rather than from a rounded on-screen figure.

Terms explained

Base unit: The single unit every value passes through during conversion — metres for length, kilograms for weight. It keeps rounding error from accumulating.
Inch (in): Exactly 2.54 cm by international agreement. Used for screen sizes, tyres and clothing measurements.
Mile (mi): 1,609.344 m, roughly 1.6 km. Standard for road distances and speed limits (mph) in the US and UK.
Pound (lb): Exactly 0.45359237 kg. Remembering it as about 453.6 g is close enough for shipping weights and body weight.
Ounce (oz): One-sixteenth of a pound, about 28.35 g. Common on cosmetics and packaged food labels.
Geun: A traditional Korean weight unit. This tool treats one geun as 600 g, the figure used at butcher counters.
Kelvin (K): A temperature scale that puts zero at absolute zero (-273.15°C). Its degree size matches Celsius, so only the offset differs.

Frequently asked questions

How do I convert Fahrenheit to Celsius by hand?

Subtract 32, then multiply by 5/9. The subtraction comes first because the two scales place their zero points differently. For a rough mental estimate, subtract 30 and halve it.

Why is an inch exactly 2.54 cm?

Because it was defined that way. The 1959 international yard and pound agreement set the inch at exactly 2.54 cm, so it is a definition rather than a measurement, and the decimals do not continue.

What is a geun?

A traditional Korean unit still used in markets. This tool calculates one geun as 600 g, which is the meat and fish standard; vegetables are often sold by a 375 g geun instead, so do not apply the result to produce.

Does it handle area, volume or speed?

No — this tool covers length, weight and temperature only. Other categories such as speed, data size and time have their own converters elsewhere on the site.

Can I see more decimal places?

The display rounds to six decimals for readability. If you need more precision, calculate from the exact conversion factors listed above.