Unit Conversion calculators

Most modern conversion factors, an inch to millimeters, a pound to kilograms, are exact defined constants by international agreement, not measured approximations. The only rounding that happens is in how many decimal places the result displays, never in the underlying factor.

They're defined differently by historical convention: a US gallon is about 3.785 liters, an imperial (UK) gallon is about 4.546 liters: roughly 20% larger. Always confirm which gallon a recipe, tank spec or fuel figure is using before converting.

Length and weight conversions are pure multiplication because both scales start at zero in the same place. Temperature scales have different zero points, Celsius and Fahrenheit don't even agree on where water freezes, so converting requires shifting the scale, not just multiplying it.

A knot is one nautical mile per hour. A nautical mile (about 1.15 land miles) is based on one minute of latitude, which is why aviation and marine navigation use knots: it maps directly onto position on a nautical chart in a way statute miles don't.

Yes: a larger overall tire diameter covers more ground per wheel rotation. So your actual speed runs faster than your speedometer indicates (which is calibrated to the stock tire size), and your odometer under-reports distance traveled.

Food labels use the capital-C Calorie for a kilocalorie, which is 1,000 small calories. The energy converter treats kilocalories and food Calories as the same unit.

There are 43,560. The area converter handles it, along with hectares, square miles and the rest.

They are different units of the same thing. One bar is about 14.5 psi, and one atmosphere is about 14.7 psi or 101.3 kilopascals.

Every fourth year adds a day, so the average calendar year is about 365.25 days. For a contract or a birthday, count calendar dates instead of using an average year.

No. A mechanical horsepower is about 745.7 watts and a metric horsepower is about 735.5. A car spec can quote either, so check which before comparing engines.

A byte is eight bits. Network speeds are quoted in bits per second and file sizes in bytes, so a 100 megabit connection moves at most 12.5 megabytes each second. A lowercase b means bits and a capital B means bytes.

They share a name and match on Earth's surface, but they measure different things. Mass is how much matter there is, and force is how hard gravity pulls on it. In newtons, one pound-force is about 4.448.

It was defined from one minute of latitude, about a sixtieth of a degree along a meridian, and fixed internationally at exactly 1,852 meters. That link to latitude is why ships and aircraft use it for navigation.

Miles per gallon divides distance by fuel. Liters per 100 kilometers divides fuel by distance, so one is the reciprocal of the other. Doubling the mpg halves the liters per 100 kilometers, which is not a straight-line change.

Subtract 32 and multiply by 5 over 9, so 68 degrees Fahrenheit is 20 degrees Celsius.

No. A US gallon is about 3.785 liters and a UK gallon is about 4.546 liters, so the two differ by roughly 20%.

Banks add a margin or fee to the market rate, so the amount you receive is usually a bit less than the converted figure.