Want to wire a 3 meter WS2812 to fire up underneath the fireplace. But looking at the specs 60mA*300LEDS thats around 18Amps. That’s a wire of around 2.5 mm to the strip itself which it will undoubtlately not able to solder to itself.
Usually you calculate with 20 mAh per LED.
You could go for 30 if you want to be safe but having all LEDs at 100% is not common with addressable LEDs.
Use power injection instead of a fat cable.
You pass power and ground from both ends of the strip. That is probably enough, but if you can hide the wire then you could inject at the middle also.