About this calculator
This length calculator converts between the seven most common length units: inches, feet, yards, miles, centimeters, meters, and kilometers. Enter a value in any one field — or combine several, such as 5 feet and 6 inches — and it adds them together and shows the total length in every unit at once.
How to use
Enter a value into any one or more of the fields above (leave the rest blank), then click Calculate to see the total length converted into all seven units. Click Clear to reset every field.
Frequently Asked Questions
Why do conversion results sometimes look imprecise?
Many unit conversions involve irrational or repeating decimal factors defined by international treaty or derived from physical constants. The result is mathematically exact — the apparent imprecision is just how the decimal expansion of the conversion factor looks. For practical use, round to the precision your application requires.
What's the most common unit conversion mistake?
Confusing mass and weight (kg vs. N vs. lbf), or confusing fluid ounces with ounces of mass. Also common: mixing US customary and Imperial units, which look identical but differ slightly (e.g., a US gallon ≠ an Imperial gallon). Always confirm which variant your source data uses.
How precise do I need to be?
It depends on your application. Cooking: ±5% is fine. Engineering and construction: ±1% or better. Scientific measurement: match the precision of your least-precise measurement instrument. There's no benefit to expressing a result to 8 decimal places if your measurement was only accurate to 2 significant figures.
Are these conversions exact or approximate?
SI-based conversions (e.g., km to m, kg to g) are exact by definition. Conversions between SI and imperial units use defined exact factors (e.g., 1 inch = exactly 25.4 mm since 1959). Conversions involving physical constants like calories or BTUs may have slightly different values depending on which definition your field uses.