Arduino Mega 2560 R3 pinout

A big Arduino with 54 digital pins, 16 analog inputs and 4 serial ports. It uses 5 V logic, so 3.3 V-only sensors need a level shifter.

Top view, USB connector on the left. Colors: red power, grey ground, green GPIO, yellow analog, orange USB serial, blue I2C.

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At a glance

Chip: ATmega2560
Processor: 8-bit AVR ATmega2560 at 16 MHz, 8 KB SRAM, 256 KB flash, 4 KB EEPROM
Logic level: 5 V. 3.3 V-only sensors need a level shifter.
Flashing tool: avrdude
Arduino board (FQBN): arduino:avr:mega
Live pin view in BoardPilot: Yes (diagnostic agent available)

Pins to avoid or use with care

USB serial: TX0→1 (PE1), RX0←0 (PE0)

Used for uploading and the serial monitor. Anything connected here can break uploads.

Good pins for LEDs, buttons and signals

22, 23, 24, 25, 26, 27, 28, 29, ~2, ~3, ~4, ~5, ~6, ~7, ~8, ~9

Default pins in Arduino

I2C: SDA = SDA 20, SCL = SCL 21. Only these pins work with the Wire library defaults. I2C only works on 20 (SDA) and 21 (SCL); the SDA/SCL pins near AREF are the same signals. Both have 10 kΩ pull-ups to 5 V on the board.
SPI: MOSI = 51, MISO = 50, SCK = 52, CS = 53.
Analog inputs: A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15 (0–5 V)

All 85 pins

Pin	GPIO	Chip pin	Functions	Notes
SCL	21	PD0	GPIO, I2C_SCL (default), INT0	Same signal as D21 (I2C clock). Has a 10 kΩ pull-up to 5 V on the board: 3.3 V-only I2C parts need a level shifter.
SDA	20	PD1	GPIO, I2C_SDA (default), INT1	Same signal as D20 (I2C data). Has a 10 kΩ pull-up to 5 V on the board: 3.3 V-only I2C parts need a level shifter.
AREF	—		ADC_REF	Analog reference input. Leave it unconnected unless your code calls analogReference(EXTERNAL); never power parts from it.
GND	—
~13	13	PB7	GPIO, PWM	The built-in LED "L" is on this pin.
~12	12	PB6	GPIO, PWM
~11	11	PB5	GPIO, PWM
~10	10	PB4	GPIO, PWM
~9	9	PH6	GPIO, PWM
~8	8	PH5	GPIO, PWM
~7	7	PH4	GPIO, PWM
~6	6	PH3	GPIO, PWM
~5	5	PE3	GPIO, PWM
~4	4	PG5	GPIO, PWM
~3	3	PE5	GPIO, INT5, PWM
~2	2	PE4	GPIO, INT4, PWM
TX0→1	1	PE1	GPIO, UART0_TX	Serial TX. Shared with the USB link: using it for parts can break uploads and the serial monitor.
RX0←0	0	PE0	GPIO, UART0_RX	Serial RX. Shared with the USB link: using it for parts can break uploads and the serial monitor.
TX3 14	14	PJ1	GPIO, UART3_TX
RX3 15	15	PJ0	GPIO, UART3_RX
TX2 16	16	PH1	GPIO, UART2_TX
RX2 17	17	PH0	GPIO, UART2_RX
TX1 18	18	PD3	GPIO, UART1_TX, INT3
RX1 19	19	PD2	GPIO, UART1_RX, INT2
SDA 20	20	PD1	GPIO, I2C_SDA (default), INT1	Default I2C SDA. Has a 10 kΩ pull-up to 5 V on the board: 3.3 V-only I2C parts need a level shifter.
SCL 21	21	PD0	GPIO, I2C_SCL (default), INT0	Default I2C SCL. Has a 10 kΩ pull-up to 5 V on the board: 3.3 V-only I2C parts need a level shifter.
IOREF	—			Tells shields that this board uses 5 V logic. Connected to 5V; not meant to power parts.
RESET	—		RESET	Reset input. Pull it LOW (or press the button) to restart the board.
3.3V	—			3.3 V output, 50 mA max. Enough for one or two small sensors.
5V	—			5 V output from USB or the on-board regulator.
GND	—
GND	—
Vin	—			Power input (7-12 V recommended) from the barrel jack or an external supply. It is not fed from USB, so do not use it to power parts.
A0	54	PF0	GPIO, ADC0
A1	55	PF1	GPIO, ADC1
A2	56	PF2	GPIO, ADC2
A3	57	PF3	GPIO, ADC3
A4	58	PF4	GPIO, ADC4
A5	59	PF5	GPIO, ADC5
A6	60	PF6	GPIO, ADC6
A7	61	PF7	GPIO, ADC7
A8	62	PK0	GPIO, ADC8
A9	63	PK1	GPIO, ADC9
A10	64	PK2	GPIO, ADC10
A11	65	PK3	GPIO, ADC11
A12	66	PK4	GPIO, ADC12
A13	67	PK5	GPIO, ADC13
A14	68	PK6	GPIO, ADC14
A15	69	PK7	GPIO, ADC15
5V	—			5 V, same rail as the 5V pin.
5V	—			5 V, same rail as the 5V pin.
22	22	PA0	GPIO
23	23	PA1	GPIO
24	24	PA2	GPIO
25	25	PA3	GPIO
26	26	PA4	GPIO
27	27	PA5	GPIO
28	28	PA6	GPIO
29	29	PA7	GPIO
30	30	PC7	GPIO
31	31	PC6	GPIO
32	32	PC5	GPIO
33	33	PC4	GPIO
34	34	PC3	GPIO
35	35	PC2	GPIO
36	36	PC1	GPIO
37	37	PC0	GPIO
38	38	PD7	GPIO
39	39	PG2	GPIO
40	40	PG1	GPIO
41	41	PG0	GPIO
42	42	PL7	GPIO
43	43	PL6	GPIO
44	44	PL5	GPIO, PWM
45	45	PL4	GPIO, PWM
46	46	PL3	GPIO, PWM
47	47	PL2	GPIO
48	48	PL1	GPIO
49	49	PL0	GPIO
50	50	PB3	GPIO, SPI_MISO (default)
51	51	PB2	GPIO, SPI_MOSI (default)
52	52	PB1	GPIO, SPI_SCK (default)
53	53	PB0	GPIO, SPI_CS (default)	SPI chip select. Keep it an OUTPUT when using SPI, or SPI can stop working.
GND	—
GND	—

Questions

Which pins are I2C on the Arduino Mega 2560 R3?

SDA is SDA 20 and SCL is SCL 21 (the defaults of the Arduino Wire library). Only certain pins support I2C in hardware, so use these unless you know your core allows others.

Which Arduino Mega 2560 R3 pins should I avoid?

TX0→1, RX0←0 (USB serial link).

Is the Arduino Mega 2560 R3 5 V tolerant?

The Arduino Mega 2560 R3 runs at 5 V, so 5 V sensors connect directly. 3.3 V-only parts need a level shifter.

Which pins can read analog voltage on the Arduino Mega 2560 R3?

A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, from 0 to 5 V.

How do I upload code to the Arduino Mega 2560 R3?

In the Arduino IDE pick the board arduino:avr:mega (core arduino:avr).

Wiring guides for the Arduino Mega 2560 R3

Step-by-step wiring, voltage checks and test code for the most used parts:

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Compare

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Learn the basics

Lesson: What is a microcontroller? Lesson: Hardware basics for software developers Lesson: GPIO: pins in and out Pinout GPIO Logic level (HIGH and LOW) Arduino Bootloader

Check your wiring with BoardPilot

BoardPilot shows this board in 3D, flags risky pins as you wire, and flashes it safely with a backup first.

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Sources

Arduino MEGA 2560 Rev3 Eagle design files, Board outline; header pads and nets (POWER, ADCL, ADCH, JP6, PWML, COMMUNICATION, XIO); RN1 10k pull-ups on SDA/SCL
Arduino Mega 2560 Rev3 datasheet (A000067), Connector pinouts; IOREF connected to 5V; VIN 7-12 V
Arduino Mega 2560 Rev3 full pinout (A000067)
Microchip ATmega640/1280/1281/2560/2561 datasheet, 1 Pin Configurations; 13.3 Alternate Port Functions; 15 External Interrupts; 26 ADC
arduino/ArduinoCore-avr variants/mega/pins_arduino.h, Arduino pin to port table, PWM timers, SPI/I2C defaults, A0 = 54
arduino/ArduinoCore-avr boards.txt, USB VID/PID, upload protocol wiring at 115200
Board data file and source notes on GitHub

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