I have a LPD8806 led powerstrip with 32 leds connected to my raspberry and it works fine on my 5v 2a power supply.. I ordered now also a 60 led version.. is there a easy formula to calculate how much amps my power supply has to be when I increase the number of leds?
Generally you would need to measure the power consumption of one LED with an ammeter (or multimeter). Than you can multiply this by 60 to get the consumption of one meter.
Easier would it be to measure the consumption of the complete strip you got and multiply the consumption by 2 to get the consumption of the new strip. That just works when you use the same lenght. If they arent, you need to divide the 30Led Strip consumption by its lenght and multiply that with 2 and the lenght of the new strip.
You could also guess it, but thats rather dangerous. If they are SMD ones, you can guess they consume 20mAh per Color when they are full on. that means one LED consumes 60mAh completely. If you multiply that by 60 LEDs per Meter you get 3,6A per Meter, which is way too much than your power supply can deliver
Without knowing the exact juice you'll need, I know the power delivered through the GPIO won't be enough. Any current pull above ~15mA (on a single pin) or ~50mA (total all pins) will result in a less stable berry. Having 5V on 4A pushed in through the microUSB won't change a thing. You'll need external power to power those leds. Apparently you've got away with it in your current setup, wherefor I'm happy for you, but I won't use this in real life.