with regard to definitions i found that
2-3mile/hour is barely felt on face and barely moves your hair and eyelashes.
4-5is felt on face and if you are looking into it the wind creates just a small bubbling sound in your ear that disturbs slightly.(listen carefully and clean your ears;))
5-7 you can notice the trees agitating and moving constantly. some of that long grass will start to tip quite at an angle.
8mile/hour is strong as that of a number 3 on a Fan and will move small plants leaves, move some debree(trap).
10mph is stronger than the fan and if your hair is abit longish, it will move to one side opposite the wind and bothers your eyes abit if you look into it for a constant moment. the bubbling sound is more prominent in your ears and hanging branches will sway a little.
11-13mph will start to flat line most flags but this depends on their size so see whats available in your area.
anything above 13mph should be moving and swaying the trees.
a 15m/hour wind will start to move those cables we have in the streets. now you have something to refer to but you need to practice. one more thing, when trying to establish wind velocity, it is very important to establish wind direction and if the wind is constant or gusting.!
for establishing wind direction you would need to turn your head slowly till you feel the wind on both ears, atleast thats the way i do it. i had also tried using one of those small eyedrop containers, make a slightly bigger hole in them and fill it with flour and puff 3 or 4 times to confirm my feeling. you have to find something you can correlate to and jot down some notes.
you don't need to read winds to +/- 1mile per hour to make hits far out but +/- 3 is important.