Learn / Pinouts / Arduino

Arduino Uno Rev3 pinout

Explore the socketed ATmega328P Arduino Uno Rev3 pinout, with digital, analogue, PWM, UART, SPI, I2C and power connections explained.

ArduinoDevelopment boardATmega328PRev3, socketed ATmega328P5 V logic32 connections20 usable GPIO

Qualified electrical ratings

recommended operating5 V voltageboard logic rail; not an input tolerance statement

Fast answers

Which GPIO should I use?

Start with what you are connecting. Click any GPIO to locate it in the interactive diagram and inspect the full reason.

Interactive shortlist

Pin colour key

RecommendedUse with careAvoidSpecial case

Recommendation and GPIOsWhy

Easy choice

Input-capable, no declared boot warning, and suitable for the ESP32 internal pull resistor.

Add an external resistor

No matching pins declared

Excellent inputs, including ADC1, but these input-only pins have no internal pull-up or pull-down.

Works with care

These pins are sampled during boot or share the programming serial connection. Your button circuit must not force the wrong reset-time level.

Do not use

No matching pins declared

Connected to the module flash. Treat these header positions as reserved.

Reference by function

See only the pins relevant to your circuit.

Each view removes the unrelated labels, then keeps the exact channel, bus role, and assignment status beside the physical board position.

01 · GPIO

GPIO pins: safe, conditional and avoid

Green pins are the easiest general-purpose choices. Amber pins have a device or board caveat. Red pins are reserved by the board or module.

Pin colour key

GPIOADCI2CSPIUARTPWM

02 · ADC

ADC analogue inputs

Only analogue-capable connections are shown, with the exact converter and channel role declared by the source data.

Pin colour key

GPIOADCI2CSPIUARTPWM

03 · I2C

I²C data and clock

Default data and clock roles are labelled separately from routes that software can remap.

Pin colour key

GPIOADCI2CSPIUARTPWM

04 · SPI

SPI buses

Usable SPI routes are shown with their controller and signal roles. Pins marked avoid are excluded from this view.

A remappable peripheral still has electrical and boot restrictions. Remapping does not make a reserved pin safe.

Pin colour key

GPIOADCI2CSPIUARTPWM

05 · UART

UART serial ports

Transmit and receive pins are grouped by UART controller, with default and fixed assignments shown explicitly.

Pin colour key

GPIOADCI2CSPIUARTPWM

06 · PWM

PWM outputs

PWM can be routed to output-capable GPIOs. Input-only pins are not included because they cannot drive a PWM waveform.

Pin colour key

GPIOADCI2CSPIUARTPWM

The classic Uno layout

This reference covers the Arduino Uno Rev3 with the socketed, dual-inline ATmega328P. Its familiar shield headers expose fourteen numbered digital pins and six analogue inputs, plus power, reset and reference connections.

Shared functions matter

Pins D0 and D1 form the hardware serial port used by the USB interface, so connected hardware can interfere with uploads and the Serial Monitor. D10–D13 carry SPI, while A4 and A5 carry I2C as SDA and SCL. The extra SDA and SCL header positions are duplicates of A4 and A5, not an additional bus.

PWM and analogue input

The ~ marking identifies the six pins supported by Arduino's analogWrite() convention: D3, D5, D6, D9, D10 and D11. A0–A5 are the primary analogue inputs and can also be addressed as digital GPIO when analogue conversion is not needed.

Power safely

The board's digital logic is 5 V. The VIN and USB limits are board power specifications, not GPIO signal limits. Always distinguish a recommended operating condition from an absolute maximum before connecting external circuits.

Quick explanations

ATmega328P pinout FAQ

Which ATmega328P GPIO pins are the easiest to use?

Start with the pins marked recommended: D2, D3, D4, D5, D6, D7, D8, D9, D10, D11, D12, A0, A1, A2, A3, A4, A5. They are declared as general-purpose GPIO without a board-specific boot, programming, or reserved-function warning in this reference. Always check the exact function you need before wiring.

Which pins can I use for a push button?

Use a recommended, input-capable GPIO. Check whether the selected pin provides an internal pull resistor or requires an external resistor.

Which analogue pins should I use while Wi-Fi is active?

Prefer the ADC1 pins: A1. On this processor, ADC2 has a wireless-use conflict recorded in the pin definition, so ADC1 is the dependable starting point when radio operation and analogue sampling must coexist.

Searchable without JavaScript

Complete pin table

Every physical connection and declared alternate function is included here for accessibility, printing and search discovery.

Physical	Pin	Input / output	General suitability	Functions	Important notes
JDIGITAL.1	D0RX, PD0	Input + Output	conditional	GPIO · fixed UART · RX · fixed	• Shared with the on-board USB-to-serial interface • Connected hardware can interfere with uploads and Serial Monitor traffic.
JDIGITAL.2	D1TX, PD1	Input + Output	conditional	GPIO · fixed UART · TX · fixed	• Shared with the on-board USB-to-serial interface • Connected hardware can interfere with uploads and Serial Monitor traffic.
JDIGITAL.3	D2INT0, PD2	Input + Output	recommended	GPIO · fixed Interrupt · INT0 · 0 · fixed
JDIGITAL.4	D3PWM, INT1, PD3	Input + Output	recommended	GPIO · fixed PWM · OC2B · fixed Interrupt · INT1 · 1 · fixed
JDIGITAL.5	D4PD4	Input + Output	recommended	GPIO · fixed Interrupt · pin-change interrupt · fixed
JDIGITAL.6	D5PWM, PD5	Input + Output	recommended	GPIO · fixed PWM · OC0B · fixed Interrupt · pin-change interrupt · fixed
JDIGITAL.7	D6PWM, PD6	Input + Output	recommended	GPIO · fixed PWM · OC0A · fixed Interrupt · pin-change interrupt · fixed
JDIGITAL.8	D7PD7	Input + Output	recommended	GPIO · fixed Interrupt · pin-change interrupt · fixed
JDIGITAL.9	D8PB0	Input + Output	recommended	GPIO · fixed Interrupt · pin-change interrupt · fixed
JDIGITAL.10	D9PWM, PB1	Input + Output	recommended	GPIO · fixed PWM · OC1A · fixed Interrupt · pin-change interrupt · fixed
JDIGITAL.11	D10PWM, SS, PB2	Input + Output	recommended	GPIO · fixed PWM · OC1B · fixed SPI · SS · fixed Interrupt · pin-change interrupt · fixed
JDIGITAL.12	D11PWM, MOSI, PB3	Input + Output	recommended	GPIO · fixed PWM · OC2A · fixed SPI · MOSI · fixed Interrupt · pin-change interrupt · fixed
JDIGITAL.13	D12MISO, PB4	Input + Output	recommended	GPIO · fixed SPI · MISO · fixed Interrupt · pin-change interrupt · fixed
JDIGITAL.14	D13SCK, LED_BUILTIN, PB5	Input + Output	conditional	GPIO · fixed SPI · SCK · fixed Interrupt · pin-change interrupt · fixed	• Connected to the on-board indicator LED
JDIGITAL.15	GND	—	unavailable	Ground · fixed
JDIGITAL.16	AREF	Input	unavailable	Power · ADC reference input · fixed
JDIGITAL.17	SDAA4 duplicate	Input + Output	conditional	I2C · SDA · fixed	• Electrically the same signal as A4
JDIGITAL.18	SCLA5 duplicate	Input + Output	conditional	I2C · SCL · fixed	• Electrically the same signal as A5
JANALOG.1	NC	—	unavailable		• Not connected.
JANALOG.2	IOREF	—Output	unavailable	Power · logic reference output · fixed	• Connected to 5 V on Uno Rev3
JANALOG.3	RESET	Input	unavailable	Reset · active-low reset · fixed
JANALOG.4	3V3	—Output	unavailable	Power · 3.3 V regulated output · fixed
JANALOG.5	5V	Input + Output	unavailable	Power · 5 V rail · fixed
JANALOG.6	GND	—	unavailable	Ground · fixed
JANALOG.7	GND	—	unavailable	Ground · fixed
JANALOG.8	VIN	Input	unavailable	Power · unregulated board input · fixed	• absolute maximum: 20 V input — VIN board input only
JANALOG.9	A0D14, PC0	Input + Output	recommended	GPIO · fixed ADC · ADC0 · 0 · fixed Interrupt · pin-change interrupt · fixed
JANALOG.10	A1D15, PC1	Input + Output	recommended	GPIO · fixed ADC · ADC1 · 1 · fixed Interrupt · pin-change interrupt · fixed
JANALOG.11	A2D16, PC2	Input + Output	recommended	GPIO · fixed ADC · ADC2 · 2 · fixed Interrupt · pin-change interrupt · fixed
JANALOG.12	A3D17, PC3	Input + Output	recommended	GPIO · fixed ADC · ADC3 · 3 · fixed Interrupt · pin-change interrupt · fixed
JANALOG.13	A4SDA, D18, PC4	Input + Output	recommended	GPIO · fixed ADC · ADC4 · 4 · fixed I2C · SDA · fixed Interrupt · pin-change interrupt · fixed
JANALOG.14	A5SCL, D19, PC5	Input + Output	recommended	GPIO · fixed ADC · ADC5 · 5 · fixed I2C · SCL · fixed Interrupt · pin-change interrupt · fixed

Qualified electrical ratings

Which GPIO should I use?

See only the pins relevant to your circuit.

GPIO pins: safe, conditional and avoid

ADC analogue inputs

I²C data and clock

SPI buses

UART serial ports

PWM outputs

The classic Uno layout

Shared functions matter

PWM and analogue input

Power safely

ATmega328P pinout FAQ

Complete pin table

Arduino Uno Rev3 project