You may have seen elsewhere on this site (in the comments on John Allen’s hub gear table in the Gears section) that Wiel van den Broek has created some very useful Excel spreadsheets for gearing choices involving hub gears and bracket gears. You can enter the tyre format, chainwheel and sprocket sizes and instantly compare the results given by different gears.
The gears covered range some more than 100 years old to others that are in current production. There is a metric (distance travelled per pedal rotation) chart and a gear inches chart (equivalent direct drive wheel diameter), both of which you can download from here: http://fietssite.jouwweb.nl/downloads
Many thanks to Wiel for creating these spreadsheets.