Determine pipe diameter with 2 known values

I'm assuming the diameter is quoted on row 8:9 that goes, 100, 125, 150, etc?

If so, in B23, type in:

Formula:

=INDEX($G$8:$M$9,1,MIN(COUNT($G$8:$M$9),MATCH(B18,OFFSET($G$11:$M$11,MATCH($B$20,$F$12:$F$21,0),0),1)+1))

Incredible, thanks a lot, that's exactly what I was looking for.

Again thank you so much.

I will investigate how the formulas are applied, and find out if I can make it work myself.

Thanks.
KJ