"Grunff" wrote in message
...
David Kerr wrote:

Err........... don't you mean 4cm diameter?
Thus radius = 2 and radius squared = 4 = diameter
(numerically, that is)

Yes! That's exactly what I mean. Or rather, I meant to say "would work
for pipes of 2cm /radius/".



Or to put it another way:-

15mm tube = 7.57 metres/litre
22mm tube = 3.18 metres/litre

;-)
Dave