one single p atch antenna gain

Can someone help me about one single p atch antenna gain?
Some one tell me the gain is like dipole only have 2~3 dbi gain.
But I see the manufactuer give me the gain is 6 ~8 dbi.
Why to make the big difference?

A simple rectangular patch (Bahl & Bhartia) gives 6.6 dBi gain.

I have been doing a lot of microstrip antennas recently. It really depends on the substrate, size, and shape. Radiation efficiency should be in your consideration as well. I saw as high as 8-9 dbi and as low as 1 dbi.

for application you want ,

normally , to meet the FCC rule .

in ISM band , for 2.4 GHz , the max gain is 3dbi

5 GHz , the max gain is 6dbi


note : the gain for reference is usually a peak gain

but , the average gain is also important .