920 kv means 920 rpm / volt .
What i understood is when i an powering that motor with 1 v it will rotate at 920 rpm .
So if it's running on 12 v its rpm will be 920*12 right ?
Since it's not  the power , how can i determine the power of a motor ?

connect a DC ammeter in between the battery and esc.... now multiply this amp reading with Voltage...
what u get is power in Watts

@a3ruz,
You may find this of some use:
http://www.rcindia.org/electric-planes/iyer's-tech-talk-how-much-power/msg196376/#msg196376

yeah Iyer sir i saw that post and this doubt was generates coz of that ,
i am still confused about the rpm and KV
itried to post this under your thread but i think that it's locked , anyway i was not able to post below that

@a3ruz,

920 kv means 920 rpm / volt . Yes.
What i understood is when i an powering that motor with 1 v it will rotate at 920 rpm. Yes.
So if it's running on 12 v its rpm will be 920*12 right ?
Yes, but without a prop, i.e., on nil load. Due to efficiency factor, it may do only say 90% of that. When you add a prop, the rpm may only be 60-75% of the kv times voltage, depending on the size of the prop (both dia and pitch).

Since it's not  the power , how can i determine the power of a motor ?
From the specification sheet, if you got one with the motor, or by looking up the manufacturer's site (eg, dys.hk) or flybrushless.com.
Use a wattmeter, at least an ammeter, if you can borrow one.

If you tell me why you want to determine the power of the motor, I could clarify further.

Basically the power would vary as a function of the load. As you increase the load, the current draw will increase, the voltage will drop, and the amps x volts will go up. The limiting factors are the max amps the motor is rated for (beyond which it will overheat/burn), and the max amps your battery is rated for. Incidentally, the C rating mentioned on average quality lipos it very optimistic. I usually do not draw over 10C from 20C rated lipos!

Hope this was of some help.
Regards.

Thanks for the reply sir, 
I had a conversation with  a local shopkeeper and he asked me about the power of the motor due to lack of my knowledge I replied it's written as 920kv and he considered it as kilo volt,  ( and did a few calculations and said me it's wrong at that potential current will flow thorough air n so ) since I don't know much about these I was not able to make him clear,   i searched in RCI n got your thread but was not able to post there ,
The thing I want to know is props n motor combination and relation between thrust, in a quad using 920 kv motors (3s) n props 9450 ( 9.4 inch diameter and 5 inch pitch right ) how much thrust does this combination produce , if it's some X then the total thrust produced will he 4*X right ? What about C rating of battery in this spec ?

@a3ruz,
Are you planning to:
1. Design and build your own quad from scratch?
2. And also learning to fly with it?

I've found these to be mutually exclusive goals, because:
1. An experimental own design needs an experienced pilot
2. A trainee pilot needs a proven design

I strongly suggest that you avoid combining these goals.

If you scratch build your very first quad, you'll still need the motors, props, ESCs, flight control board, power distribution board, bullet connectors, connecting wires between FCB and Rx, lipos, charger and radio. The only thing homemade will be the quad arms.
No point in reinventing the wheel.

The way I learnt was by getting
- a mini quad from a forum member for about 1700
- an ST360 from Quadkopters for about 6-7000

If you still propose to design your own quad from scratch, let me know, and I'll list the issues you'll have to tackle.
Regards.

No plan for a scratch build sir ! I am still in collection for the different parts !