Unit Converter
Convert between different units of length, weight, and temperature
How to Use
- Pick Length, Weight, or Temperature
- Type the value you want to convert
- Select the "From" and "To" units
- Read the result — it updates as you type
Inside the Math (and Where Floats Bite)
Length and weight conversions are just multiplication by a constant defined in the SI brochure: the inch has been exactly 25.4 mm since the 1959 international yard and pound agreement, and the avoirdupois pound is exactly 0.45359237 kg. Those aren't rounded — they're definitions. So 100 lb → kg should give you 45.359237 every time.
Temperature is the odd one out because the scales don't share a zero. Celsius and Fahrenheit are affine, not linear: F = C × 9/5 + 32. The 32 offset is why "double the temperature" means nothing in Fahrenheit. Kelvin at least shares a scale with Celsius — K = C + 273.15 — and is the only one with a true zero point.
One thing this tool can't fully escape: IEEE 754 double-precision floats. Convert 0.1 kg to pounds and back, and you may see 0.09999999999999998 rather than 0.1. That's not a bug in the ratio — it's that 0.1 doesn't have a finite binary representation. For most everyday use this is invisible, but if you're doing legal-for-trade weighing or aerospace work, use a decimal library (JavaScript's BigDecimal proposal, or Python's decimal) and pin the ratios as exact fractions. Source: NIST SP 811, "Guide for the Use of the International System of Units."