For example a 30" stove (2.5') x 100 CFM= Approx. 250 CFM needed, as a minimum.
But we can't just stop there...
A range hood should exchange the air in the kitchen 15 x per hour.
If your kitchen is 12' x 15' and 10' high, that equals 1,800 cubic feet. To find the size of fan needed, multiply the cubic feet x the # of air exchanges (15) then divide by 60 (minutes in an hour).
In our example that would be: 1,800 x 15 = 27,000 divided by 60 = 450. You need 450 CFM minimum for this size of kitchen.
Now we aren't quite finished. What about the size of the duct work, number of turns, etc.? Most HVAC suppliers recommend smooth 8" metal pipe. Add 1 CFM per foot of pipe and add 25 CFM for each bend and 40 CFM for the roof cap. Let's estimate this example as being 100 CFM needed.
Now, we ARE finished. Take the rating for the stove width (250 CFM in our example), room size (450 CFM minimum), burner type (500 CFM minimum). The highest number is 500, then add your duct work CFM calculations (100) and you would need a total of 600 CFM for this range size, kitchen size, range burner and ductwork.
I hope this helps. Be sure to discuss this with your contractor and appliance providers.