A field guide from MeasureWise
A familiar name can hide a different unit
An ounce can mean mass or fluid volume. A ton can refer to a metric tonne or a different customary unit. A foot can use an international definition or an older surveying definition. MeasureWise chooses a specific definition and lists it beside the converter. Before using a number in a report, match the definition to the source document rather than relying on the short unit name alone.
Convert through a common base
Most linear conversions on this site multiply the source value by a factor to reach a base unit, then divide by the target factor. This makes a round trip easy to reason about. Temperature is different: Fahrenheit and Celsius have different zero points, so conversion includes an offset as well as a scale. Converting a temperature interval requires a different rule from converting a measured temperature.
Square units really are squared
Area does not use the same factor as length. Because a square has two independent dimensions, the length factor must be squared. Ten feet of length and ten square feet of area therefore produce very different metric numbers. Always check whether a quantity is length, area, volume, mass, or pressure before opening a converter.
Round at the end
Keep extra digits during intermediate work and round only when presenting a final value. A display with many decimal places does not mean the original measurement had that precision. For example, a room measured only to the nearest centimeter does not become a micrometer-accurate room when converted to feet. Record the original measurement, its unit, and the final rounding rule if reproducibility matters.