20 inches is about 1.36 wavelengths, which gives 10.6 dBd.
24 inches is about 1.63 wavelengths, which gives 11.2 dBd.

These numbers are specifically for yagis, not quads, quagis, or loop
yagis, but should be pretty close regardless of type as booms get long.

tom
K0TAR

coyotefred wrote:

Wow...so those smaller yagis in the 20-24" length would, despite being
advertised as giving you 12-14dB gain, would likely only be giving you
4-5dB?

Tom Ring wrote in message ...

A 60 inch antenna at 800 megs is about 4.07 wavelengths. Plugging that
into the boomlength to practical gain formula gives 14.2 dBd. A super
tweaked one might give .2 or .3 more, but the bandwidth would be worse.