Each segment of 3 LEDs draws approximately 20 milliAmperes from a 12V supply, per string of LEDs. So for each segment, there is a maximum 20mA draw from the red LEDs, 20mA draw from the green and 20mA from the blue. If you have the LED strip on full white (all LEDs lit) that would be 60mA per segment.
To find the total maximum current draw per meter, we would multiply 60mA x 10 (ten segments per meter for the 30/LED per meter strip) = 0.6 Amps per meter OR 60mA x 20 (twenty segments per meter for the 60/LED per meter strip) = 1.2 Amps per meter. Again, that's assuming you would have all the LEDs on at once and that you are powering it from 12V. If you're going to be PWM-fading between colors, maybe 1/2 of that is what you'll be drawing. Still, you do need to have a fairly decent power supply to run this strip, all those LEDs add up!