Metric and US units, side by side
The United States uses US customary units — inches, feet, pounds, gallons, degrees Fahrenheit — while most of the world uses the metric system. Since 1959 the two have been tied together by exact definitions: one inch is exactly 2.54 centimeters and one pound is exactly 0.45359237 kilograms. That means every conversion here is exact; results are only rounded for display.
Tips for accurate conversions
- Check which gallon or ounce you mean. US and UK (imperial) gallons and fluid ounces are different sizes, and a fluid ounce (volume) is not the same as an ounce of weight.
- Round at the end. Convert the full value first, then round the result — rounding early adds up errors.
- Use the chart for quick lookups. Each converter has a table of the most common values, handy for printing or bookmarking.