This should be simple question and there are some simple equations out there using keg pressure and line resistance that may get you close.

A really good article that takes many things (too many things?…your final gravity..) that can be found here http://www.mikesoltys.com/2012/09/17/determining-proper-hose-length-for-your-kegerator/

The calculator is pretty bonza as well ..if you live in the imperial world.

The real factor here , which is quite significant, have a play with it, is time to pour a pint , a US Pint or about a schooner.

Using this calculator I have derived a pretty good fit form which you will see below. I have allowed for a carbonation of about 2.25 volumes at Canberra altitude. This is low end basic beers, a bit high for English ales but you can adjust by guesswork. I have also set the hose ID at 5mm and agree that 10 seconds is a nice Goldilocks time.