Exact definitions, not approximations
Since 1959, the international yard and pound have been defined in metric terms: exactly 2.54 cm to the inch and 453.59237 g to the pound. Every conversion here derives from those exact definitions — values are converted to a base unit (meters, kilograms, liters) and back out, then rounded to six significant digits for display.
The conversions people trip over
US and imperial (UK) units share names but not sizes: a US gallon is 3.785 liters while an imperial gallon is 4.546 liters, and fluid ounces differ by about 4%. This tool uses US volume measures. Temperature is the other odd one out — °C, °F, and K are offset scales, not multiples, so they convert through formulas (°F = °C × 9/5 + 32) rather than a single factor, and negative results are perfectly normal.
Quick landmarks worth memorizing
A meter is about 10% longer than a yard; a kilogram is about 2.2 pounds; a mile is roughly 1.6 km and a marathon about 42 km; room temperature is ~20°C / 68°F; and 100 km/h is about 62 mph. Landmarks like these let you sanity-check any conversion at a glance — including this tool's.
How to use this converter
Choose a category first — length, weight, volume, temperature, area, or speed — then type a value in any unit. The tool converts your number to that category's base unit internally and displays every other unit at once, so you see all equivalents in a single table rather than converting one pair at a time.
A worked example
Convert 5 kilometers to miles. Internally the tool holds the exact factor 1 mile = 1609.344 meters, so 5,000 m ÷ 1609.344 = 3.107 miles, and the same value shows as 5,468 yards and 16,404 feet in the table. Temperature works differently: entering 25°C runs the offset formula 25 × 9/5 + 32 = 77°F and 298.15 K — a reminder that temperature converts through formulas, not a single multiplier.