user16198: I was wondering how much my Arduino I/O pin can output when it is set at Output and is at High.
I am using an Arduino Uno R3.
Thanks in Advanced.

user7859: 40.0mA.
The Arduino UNO Digital IO pins are connected directly to the IO pins on the ATMEGA328P processor.
From page 299 of the data sheet for that processor...

Note that there is also a total current limit for all output pins combined, and that the voltage starts to drop as the current goes up. 

16198: <p>I was wondering how much my Arduino I/O pin can output when it is set at <strong>Output</strong> and is at <strong>High</strong>.</p>

<p>I am using an <strong>Arduino Uno R3</strong>.</p>

<p>Thanks in Advanced.</p>
 7859: <p>40.0mA.</p>

<p>The Arduino UNO Digital IO pins are connected directly to the IO pins on the ATMEGA328P processor.</p>

<p>From page 299 of the <a href="https://www.google.com/url?sa=t&amp;rct=j&amp;q=&amp;esrc=s&amp;source=web&amp;cd=1&amp;cad=rja&amp;uact=8&amp;ved=0ahUKEwi3p_GkrpnKAhWEQyYKHVBiCJUQFggjMAA&amp;url=http%3A%2F%2Fwww.atmel.com%2Fimages%2Fatmel-8271-8-bit-avr-microcontroller-atmega48a-48pa-88a-88pa-168a-168pa-328-328p_datasheet_complete.pdf&amp;usg=AFQjCNEfBUXFG85G6huz6IpUbv0LQqhvGQ&amp;sig2=9zwktRebt6GXlhApMf7Zzg" rel="noreferrer">data sheet</a> for that processor...</p>

<p><a href="https://i.stack.imgur.com/Brff1.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/Brff1.jpg" alt="enter image description here"></a></p>

<p>Note that there is also a total current limit for all output pins combined, and that the voltage starts to drop as the current goes up. </p>
