It's a rough guide,about right.
Depends on the driller set up you are comparing it to.
Basically take the front chainwheel tooth count d3 equals 52 ish and divide by the back cog. This gives you the wheels revs per pedal. Then times by the wheel diameter.

Ok that gives you the gear in mm or inches. you can compair that to a 28 to 112 figure for a standard bike.
However for an internal gear you need to take in to account underdrive and overdrive. Of the top of my head it's about 40 percent decreased on the sa r speed and a simular overdrive figures.

Get the figures and put it through seldon brown gear calculate to be precise.
Hope this helps.
Ps it's a cheap and simple job to alter the rear cog size if you find its an issue.