Nah. There's no direct size-intensity relationship.
As it is, the F scale is horribly abused. It's a DAMAGE measurement, not a wind speed measurement, but the damage is roughly correlated with a wind speed.
The ONLY measure of a tornado on the F scale is by a NWS team examining the damage the next day. You can't even F-rate a tornado at all if it just goes through a cornfield, really. But now news stations and whatnot are trying to instantly guesstimate F ratings (and usually inflating them).