Cable sizing worked on cross sectional area ?

[cider]

Hi. Recently tried measuring a conductor to gauge it's size. The electrician who knows his stuff said it was 4mm stranded just by looking at it and I didn't disbelieve him but then I remembered I had a set of measuring gauges in the van so measured the cross sectional diameter and it was way smaller so then we measured some 2.5mm twin & earth and again the gauges read lots smaller.
Anyway this got me thinking were we missing a trick and the cable sizes are cross sectional area not diameter ? So pye x radius ?[/list]

 

[PrenticeBoyofDerry]

Electrical cable is measured by it's CSA.
//www.diynot.com/wiki/Electrics:flatpvccables

 

[RF Lighting]

Correct. Measure one strand, divide diameter by two (radius). Square the radius (times it by it's self) then time this answer by π (pi) , and times by the number of strands. (normally seven in stranded cable)

 

[Taylortwocities]

Its because we are all lazy, and that includes the electrical suppliers (who should know better)
see http://www.tlc-direct.co.uk/Products/CA1dot5G.html

The correct description should be 2.5mm² Twin and Earth