Arduino Uno Pinout
All Uno R3 pin functions: PWM / UART / SPI / I2C / interrupts.
What it does: Look up what each Arduino Uno pin does and which peripherals it shares.
When to use it: When wiring up, choosing PWM/I2C/SPI pins, or troubleshooting pin conflicts.
Disclaimer: This result is a reference estimate. For actual production, refer to the device datasheet / local regulations as authoritative.
~ = PWM? -capable. Click the chips to filter by category.
| Pin | Category | Alternate functions | MCU | Notes |
|---|---|---|---|---|
| D0 | Digital | RX ← serial receive | PD0 | Used by upload/serial communication — avoid repurposing. |
| D1 | Digital | TX → serial transmit | PD1 | Used by upload/serial communication. |
| D2 | Digital | External interrupt INT0 | PD2 | Usable with attachInterrupt. |
| D3 | Digital | PWM ~ · External interrupt INT1 | PD3 | |
| D4 | Digital | General-purpose I/O | PD4 | |
| D5 | Digital | PWM ~ | PD5 | |
| D6 | Digital | PWM ~ | PD6 | |
| D7 | Digital | General-purpose I/O | PD7 | |
| D8 | Digital | General-purpose I/O | PB0 | |
| D9 | Digital | PWM ~ | PB1 | |
| D10 | Digital | PWM ~ · SPI SS | PB2 | |
| D11 | Digital | PWM ~ · SPI MOSI | PB3 | |
| D12 | Digital | SPI MISO | PB4 | |
| D13 | Digital | SPI SCK · On-board LED | PB5 | Connected to the on-board LED — be careful when using as input. |
| A0 | Analog | Analog input · Digital D14 | PC0 | |
| A1 | Analog | Analog input · Digital D15 | PC1 | |
| A2 | Analog | Analog input · Digital D16 | PC2 | |
| A3 | Analog | Analog input · Digital D17 | PC3 | |
| A4 | Analog | Analog input · I2C SDA | PC4 | Default I2C data line. |
| A5 | Analog | Analog input · I2C SCL | PC5 | Default I2C clock line. |
| VIN | Power/control | External supply input (7–12V) | — | Goes through the on-board regulator. |
| 5V | Power/control | 5V output / logic level | — | |
| 3V3 | Power/control | 3.3V output (≤50mA) | — | Supplied by the on-board regulator; limited current. |
| GND | Power/control | Ground | — | Multiple GND pins at the same potential. |
| RESET | Power/control | Reset (active-low) | PC6 | Pull low to reset the MCU. |
| IOREF | Power/control | IO reference voltage | — | 5V on the Uno; lets shields detect the logic level. |
| AREF | Power/control | ADC reference voltage | — | Can take an external reference; configure with analogReference(). |
MEANS D13 drives the on-board LED; A4/A5 double as I2C; PWM pins are marked ~. An alternate-function pin can only do one thing at a time.
No history yet. Each calculation is automatically saved to this device.
How to use the Arduino Uno pinout reference
Filter by category → check alternate functions → wire by function.
- 01
Browse by category
Three groups: digital D0–D13, analog A0–A5, power/control; click the chips above to filter.
- 02
Spot the alternate functions
~ means PWM-capable; UART, SPI, I2C, external interrupts and the matching ATmega328P ports are marked too.
- 03
Pick pins by function when wiring
For example, use A4(SDA)/A5(SCL) for I2C, and 3/5/6/9/10/11 for PWM.
Common function pins at a glance
The groups people ask about most — match them up directly.
| Function | Pin |
|---|---|
| PWM (~) | D3 · D5 · D6 · D9 · D10 · D11 |
| Hardware UART | D0=RX · D1=TX |
| SPI | D10=SS · D11=MOSI · D12=MISO · D13=SCK |
| I2C | A4=SDA · A5=SCL |
| External interrupts | D2=INT0 · D3=INT1 |
Official Arduino Uno R3 pinout / ATmega328P.
Common questions, answered in 3 minutes
Why should D13 not be casually used as an input?
D13 is wired to the on-board LED and a current-limiting resistor, so as a high-impedance input it gets pulled low and reads unreliably; using it as an output / to drive an LED is fine.
Can the analog pins be used as digital?
Yes. A0–A5 are also digital D14–D19 and can digitalRead/Write; A4/A5 additionally double as I2C.
How much current can the 3V3 pin supply?
Provided by the on-board regulator, usually ≤50mA, so don't drive large loads directly from it.
What's the difference between VIN and 5V?
VIN is the external power input (about 7–12V, through the on-board regulator); 5V is the regulated logic-level output. Don't feed high voltage into the 5V pin.
Does this table apply to the Uno R4 / Nano?
This table is for the classic Uno R3 (ATmega328P). The R4, Nano, Mega, and Leonardo have different alternate functions — refer to their own pinouts as authoritative.
Standards and sources referenced by this tool
| Item | Value / Formula | Source |
|---|---|---|
| Pin functions | Uno R3 / ATmega328P | Arduino official |
| PWM pins | 3,5,6,9,10,11 | Timer0/1/2 |
Refer to the official pinout / board silkscreen as authoritative; this table is for the classic Uno R3.