Engineering Unit Converter

How the conversion actually works

Every category except temperature uses the same method: each unit carries a fixed factor that expresses it in a base unit — meters for length, kilograms for mass, pascals for pressure, joules for energy. Your input is multiplied into the base unit, then divided out into the target unit. That is exactly the formula line shown under the result, so you can copy the factors straight into a spreadsheet or an assignment and reproduce the number yourself.

The factors are not rounded conveniences. The inch, foot, yard, mile, and pound have been defined exactly in metric terms by international agreement since 1959: an inch is exactly 25.4 mm, a pound exactly 0.45359237 kg, a mile exactly 1,609.344 m. When this tool says 5 miles is 8.047 km, the only rounding is in the display — the underlying arithmetic is exact. That matters for engineering specs, where a chain of casually rounded conversions can drift enough to fail a tolerance.

Temperature is the odd one out

Celsius, Fahrenheit, and Kelvin do not share a zero, so no single multiplication converts between them. The tool routes every temperature through Celsius using the full equations — °C = (°F − 32) × 5/9 on the way in, K = °C + 273.15 on the way out. Kelvin has no degree symbol and no negative values because it starts at absolute zero; the other two scales put zero at arbitrary points, which is why they can go negative and why −40 °C and −40 °F land on exactly the same temperature.

The classic mistake is converting a temperature difference as if it were a temperature reading. A 10 °C rise is an 18 °F rise — you scale by 9/5 but do not add the 32, because the offset cancels when you subtract two readings. If a datasheet says a component heats up by 25 °C under load, that is a 45 °F rise, not a 77 °F one.

Data size: why 1 TB never looks like 1 TB

The data category uses binary steps — each unit is 1,024 of the one below, matching how operating systems report file and drive sizes. Storage manufacturers use decimal steps of 1,000 instead. Both are legitimate, but they diverge more at every level: a drive sold as 1 TB holds one trillion bytes, and one trillion bytes divided by the binary gigabyte of 1,073,741,824 bytes comes to about 931.32 GB. Your operating system is not hiding 69 GB; it is counting in a different base. The gap is why standards bodies introduced the KiB/MiB/GiB names for the binary units, though everyday usage still mixes the two freely.

Reference points worth memorizing

A few conversions come up so often that knowing the rough answer helps you sanity-check any tool, including this one. 100 km/h is 62.14 mph — so the highway rule of thumb “multiply km/h by 0.6” runs slightly low. Six feet is 182.88 cm. A typical car tyre pressure of 30 psi is about 2.07 bar. An acre is exactly 43,560 square feet — one of the few imperial definitions that is a round number in imperial rather than metric — and a hectare is about 2.47 acres. One kilowatt-hour, the unit on your electricity bill, is about 860 kcal of energy. A knot is exactly 1.852 km/h, because it was redefined as one nautical mile per hour after the nautical mile was fixed in metric terms.

If a converted result surprises you, check the category first. Ounces are the most common trap: the mass ounce (about 28.35 g) and the US fluid ounce (a volume) are different quantities that happen to share a name, and no converter can translate between them without knowing the density of what you are measuring.

Precision and display

Results show up to ten decimal places, and values above a billion or below a millionth switch to scientific notation so significant digits stay readable. The precision shown is the precision of the arithmetic, not of your measurement — if you measured a room to the nearest centimeter, the eighth decimal place of the converted figure is noise. Round the output to the precision of your input when you write it down; keep full precision only while a calculation is still in progress.

Frequently asked questions