Some European airgun manufactures quote the power output of their products using a Joules figure.

To convert this Joules figure into our more familiar ftlbs unit of measurement, simply divide the figure for Joules by 1.355817948.

So to work out the power (in ftlbs) of an airgun producing 13.5 Joules, we divide 13.5 by 1.355817948, which gives us a ftlb figure of 10.69.

To convert ftlbs into Joules, you simply go the other way, and multiply the ftlb figure by 1.355817948.