We seem to have a mix of cyclists including ones who use metric/SI units of measurement and ones who use British Imperial/US units of measurement.
I have found it convenient in the past when writing trip reports to embed scripts in my web-site that let viewers choose which kind of units they want to see (many yanks like myself prefer SI distances when calculating grades, but can't let go of Fahrenheit). I automatically detect quantities (number + unit) in text and convert them and then use CSS styling to show whichever they prefer.
Does bicycles.se think automatic unit conversion would be helpful? If so I'm happy to help the admins integrate it.
I have written unit-systems for electro-mechanical simulation software before, but this is a much scaled down version and was done specifically for cycling discussions, so it comes with some caveats. From the source comments:
// CAVEAT: // This script does not attempt to // - infer the difference between delta temperatures and absolute temperatures, // e.g. "The temperature dropped 5 celsius" should be // "The temperature dropped 9 fahrenheit" not // "The temperature dropped 41 fahrenheit" // though the web page author may give hints: // <span class="unit-delta">5 celsius</span>. // - convert other unit types or handle arbitrary unit expressions N/m2. // - handle non-English text. // - handle numbers written in non-US non-British style with a comma as the // decimal point: "1.000,5 kg". // - distinguish between pounds-mass and pounds-force. // - deal with extremely precise measurements. // Results are formatted to 3 decimal places. // - convert precisions : 5 m +/- 2 cm. // - normalize units : .1 lbs -> 45.4 g instead of 0.0454 kg. // - distinguish between different Imperial and US measures with the same // name. Most of these are volumetric (oz, quart, gallon) or obscure. // - convert between inches and cm because those are often used in // cycling as speced numbers. // Per http://sheldonbrown.com/tire-sizing.html // Bicycle tires come in a bewildering variety of sizes. // To make matters worse, in the early days of cycling, // every country that manufactured bicycles developed // its own system of marking the sizes. These different // national sizing schemes created a situation in which // the same size tire would be known by different numbers // in different countries. Even worse, different-sized // tires that were not interchangeable with one another // were often marked with the same numbers!