Everything you know about dipole (calculators) is wrong ...

I am looking forward to your correct dipole calculator, Onno. Allen VK6XL

 

And then multiply by the velocity factor. For 14 AWG stranded copper-ish stuff you get at Ham Depot, the VF is pretty close to 0.95, which will make 120.175 feet, or about 60 feet 1 inch per leg.

 

The 468/f formula already accounts for velocity factor, which is around .98 for insulated wire. The formula gets you "in the ballpark", there are FAR TOO MANY variables that are dependent on location, surrounding objects, height above ground, etc., to enable a precise calculation to be determined before the antenna is installed. Even then, changing environmental conditions, such as rain, snow, foilage on nearby trees, etc., will affect the antenna feedpoint impedance after it is installed. The only practical way to ALWAYS have a 1:1 match to an efficient antenna system is to use a tuner.

 

I stand corrected...you are right about the "468" already including the VF :

300 / 2 X 39.37 / 12 X 0.95 = 468 if the VF is about 0.95

Whenever I use the "468" rule, I nearly always end up further multiplying the result by 0.95 to get really "close" to 1.1:1 to 1.2:1 SWR. And that usually assumes a flat-top configuration, 20 feet in the air, no nearby obstructions, and Utah residential ground, and typical Utah humidity. There are other factors that affect the SWR, but these seem to be the biggest.