CFM are cubic feet per minute, basically it's the amount of air exchanged every minute in the grow box. If you calculate Width x Length x Height you get the total volume of the grow box, and then multiply that number by three (or 5) [because you want the air inside the growbox to be exchanged every 3-5 minutes]. And that is your cfm rating.
Unfortunately you have to do that in inches and then just convert the final number, there are tons of cfm to m3/h converters on the net.
I didn't check your fans, but they could be good. Also, make sure that your intake fan is less powerful (less cfm or m3/h ratings than your outtake).
There are a few options for you, although I don't know if you are aware of them yet:
Passive intake vs. active intake:
you have an active intake (if I'm not mistaken), but for such a intake to work, the outtake MUST be more powerful than the intake. If not, the outtake fan won't be able to keep up with the amount of air being transfered into the box, and basically what will happen, is that all the excess air will be pushed out of every crack (which will result in the odour escaping).
Passive intakes are when you have just one fan which pushes the air out of the box and because of the negative pressure (science) the air from the outside rushes in through intake holes). This is when you need to calculate the cfm rating and what not.
That's just a fast line out of a few options.
Now I'm high as a kite as of this moment and I could of missed something crucial and/or wrote a load of bollocks.
I like the grow box mate looks real good, listen to the other guys opinions and you'll be right as rain.
