How many amps does a 300 LED WS2812B strip draw?

At ~60 mA full white: 300 × 0.06 = 18 A on 5V before duty cycle. Mixed colors draw less.

Why size fuses above average draw?

Inrush and full-white peaks. A little headroom avoids nuisance trips.

Is duty cycle the same as app brightness?

Roughly - 50% brightness is not always half the watts, but it is a useful planning dial.

Tools / LED Amp Draw Calculator

LED Amp Draw Calculator

Free LED amp draw calculator: estimate current from LED count and mA, strip watts per meter, or total watts at 5V/12V/24V.

Calculate from Voltage (V) Duty / brightness (%) LED count mA per LED (full) Length Unit Watts per meter Total watts

Current draw—

Power—

Fuse / breaker suggestion—

Amp draw for LED strips and controllers

Amps = (LED count × mA × duty) ÷ 1000, or watts ÷ volts. Controllers, barrel jacks, and thin PCB traces all have current limits - not just the wall brick.

Pair with the power supply calculator and voltage drop tool for long runs.

LED Amp Draw Calculator

Amp draw for LED strips and controllers

Control the lights after you wire them