What is the port size difference between 318 and 340-360 heads

So I've been reading tons of threads lately about engine building, and different combos and such. Keep hearing the intakes like the Eddy-performer have smaller "318 sized" ports.

What exactly are the measurements of intake ports on a 318 head vs a 340/360 head? Or how much difference is there?

Several of the intakes I'm looking at say their ports are 1.96"x1.00", but they say they are for 318-340-and 360, so just wonder how this corresponds to the actual intake ports on the heads