Raspberry Pi GPIO Pinout: The Ultimate Reference

Introduction

The GPIO (General Purpose Input/Output) pins are the heart of what makes the Raspberry Pi so powerful as a maker platform. Unlike a regular computer, the Pi gives you direct, programmable access to hardware — sensors, motors, LEDs, displays, relays, and virtually any electronic component you can imagine.

Whether you're a beginner blinking your first LED or an advanced maker building a home automation system, this guide is your go-to reference for every single pin on the 40-pin GPIO header found on the Raspberry Pi 2, 3, 4, 5, and Zero series.

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The 40-Pin Header at a Glance

All modern Raspberry Pi models share the same 40-pin GPIO header layout, making your projects portable across generations.

Pin Numbering Systems

This is one of the most common sources of confusion. There are two ways to refer to GPIO pins:

System	Also Called	Example
BCM	GPIO numbering	GPIO17 = the 17th Broadcom GPIO
BOARD	Physical numbering	Pin 11 = the 11th physical pin on the header

In Python with the RPi.GPIO library:

import RPi.GPIO as GPIO

# Use BCM numbering (recommended)
GPIO.setmode(GPIO.BCM)

# OR use physical board pin numbers
GPIO.setmode(GPIO.BOARD)

Physical Pin	BCM GPIO	Name	Function
1	—	3.3V Power	3.3V supply (max 50mA total)
2	—	5V Power	5V supply direct from USB
3	GPIO2	SDA1	I²C Data
4	—	5V Power	5V supply
5	GPIO3	SCL1	I²C Clock
6	—	GND	Ground
7	GPIO4	GPCLK0	General Purpose Clock
8	GPIO14	TXD0	UART Transmit
9	—	GND	Ground
10	GPIO15	RXD0	UART Receive
11	GPIO17	—	General Purpose
12	GPIO18	PCM_CLK	PWM0 / PCM Clock
13	GPIO27	—	General Purpose
14	—	GND	Ground
15	GPIO22	—	General Purpose
16	GPIO23	—	General Purpose
17	—	3.3V Power	3.3V supply
18	GPIO24	—	General Purpose
19	GPIO10	SPI0_MOSI	SPI Data (Master Out)
20	—	GND	Ground
21	GPIO9	SPI0_MISO	SPI Data (Master In)
22	GPIO25	—	General Purpose
23	GPIO11	SPI0_SCLK	SPI Clock
24	GPIO8	SPI0_CE0_N	SPI Chip Enable 0
25	—	GND	Ground
26	GPIO7	SPI0_CE1_N	SPI Chip Enable 1
27	GPIO0	ID_SD	EEPROM I²C Data (HAT ID)
28	GPIO1	ID_SC	EEPROM I²C Clock (HAT ID)
29	GPIO5	—	General Purpose
30	—	GND	Ground
31	GPIO6	—	General Purpose
32	GPIO12	PWM0	PWM Channel 0
33	GPIO13	PWM1	PWM Channel 1
34	—	GND	Ground
35	GPIO19	SPI1_MISO	SPI1 / PCM FS
36	GPIO16	SPI1_CE0_N	SPI1 Chip Enable
37	GPIO26	—	General Purpose
38	GPIO20	SPI1_MOSI	SPI1 Data In
39	—	GND	Ground
40	GPIO21	SPI1_SCLK	SPI1 Clock

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Pin Categories Explained

🔴 Power Pins

The Pi provides two voltage rails on the header:

• 3.3V (Pins 1, 17) — All GPIO pins operate at 3.3V logic. Total current limit is ~50mA across all 3.3V pins combined.
• 5V (Pins 2, 4) — Directly connected to your USB power supply. Useful for powering 5V peripherals, but bypasses the Pi's protection circuitry.
• GND (Pins 6, 9, 14, 20, 25, 30, 34, 39) — Multiple ground pins distributed across the header for convenience.

🚨 Danger: GPIO pins are 3.3V logic only. Applying 5V to a GPIO pin will damage your Pi permanently. Always use a logic level shifter when interfacing with 5V devices.

🟡 General Purpose Pins

Most GPIO pins can be configured as either input or output in software:

import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)

# Configure GPIO17 as output (e.g. an LED)
GPIO.setup(17, GPIO.OUT)

# Configure GPIO27 as input with internal pull-up resistor
GPIO.setup(27, GPIO.IN, pull_up_down=GPIO.PUD_UP)

# Blink an LED
try:
while True:
GPIO.output(17, GPIO.HIGH)
time.sleep(0.5)
GPIO.output(17, GPIO.LOW)
time.sleep(0.5)
except KeyboardInterrupt:
GPIO.cleanup()

💡 Always call GPIO.cleanup() at the end of your script to reset all pins to their default state. Skipping this can cause issues with your next script run.

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🔵 I²C — Pins 3 (SDA) and 5 (SCL)

I²C (Inter-Integrated Circuit) is a two-wire serial protocol that lets you chain multiple devices on the same two wires using unique addresses.

Enable I²C on the Pi:

sudo raspi-config
# Navigate to: Interface Options → I2C → Enable

Scan for connected I²C devices:

sudo i2cdetect -y 1

Common I²C devices:

Device	Default I²C Address	Use
MPU-6050	0x68	Gyroscope + Accelerometer
BMP280	0x76 or 0x77	Temperature + Pressure
SSD1306 OLED	0x3C	128×64 Display
PCF8574	0x20–0x27	GPIO Expander
DS3231 RTC	0x68	Real-Time Clock

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🟢 SPI — Pins 19, 21, 23, 24, 26

SPI (Serial Peripheral Interface) is faster than I²C but uses more wires. It's ideal for high-speed peripherals like displays and ADCs.

Pin	BCM	SPI Role
19	GPIO10	MOSI — Master sends data
21	GPIO9	MISO — Pi receives data
23	GPIO11	SCLK — Clock signal
24	GPIO8	CE0 — Chip select device 0
26	GPIO7	CE1 — Chip select device 1

Enable SPI:

sudo raspi-config
# Navigate to: Interface Options → SPI → Enable

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🟠 UART — Pins 8 (TX) and 10 (RX)

UART is used for serial communication — connecting GPS modules, Bluetooth adapters, or another microcontroller like an Arduino.

⚠️ Warning: On Raspberry Pi 3 and 4, the primary UART is used by Bluetooth by default. You may need to disable Bluetooth or use the mini UART (ttyS0) instead of the full UART (ttyAMA0).

Disable Bluetooth to free up the full UART (Pi 3/4 only):

# Add to /boot/config.txt
dtoverlay=disable-bt

sudo systemctl disable hciuart
sudo reboot

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🟣 PWM — Pins 12 (GPIO18) and 33 (GPIO13)

PWM (Pulse Width Modulation) lets you simulate analog output — perfect for dimming LEDs, controlling servo motors, or generating audio tones.

import RPi.GPIO as GPIO

GPIO.setmode(GPIO.BCM)
GPIO.setup(18, GPIO.OUT)

# Create PWM instance: pin 18, frequency 1000Hz
pwm = GPIO.PWM(18, 1000)
pwm.start(0)  # Start with 0% duty cycle

# Fade an LED from 0% to 100% brightness
for duty in range(0, 101, 5):
pwm.ChangeDutyCycle(duty)
time.sleep(0.05)

pwm.stop()
GPIO.cleanup()

Electrical Limits — Don't Fry Your Pi

These are hard limits. Exceeding them risks permanent damage:

Spec	Limit
GPIO voltage (input/output)	3.3V max
Max current per GPIO pin	16mA
Max total GPIO current	50mA
5V pin current	Limited by your PSU
3.3V rail total current	~800mA (Pi 4)

Always use a current-limiting resistor with LEDs:

R = (Vsupply - Vled) / Iled
R = (3.3V - 2.0V) / 0.01A = 130Ω → use 150Ω or 220Ω

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Python Quick-Start Cheat Sheet

import RPi.GPIO as GPIO
import time

# ── Setup ──────────────────────────────────────────
GPIO.setmode(GPIO.BCM)          # Use BCM pin numbering
GPIO.setwarnings(False)

# ── Output ─────────────────────────────────────────
GPIO.setup(17, GPIO.OUT)        # Set GPIO17 as output
GPIO.output(17, GPIO.HIGH)      # Turn on
GPIO.output(17, GPIO.LOW)       # Turn off

# ── Input ──────────────────────────────────────────
GPIO.setup(27, GPIO.IN, pull_up_down=GPIO.PUD_UP)
state = GPIO.input(27)          # Read: 1 = HIGH, 0 = LOW

# ── Interrupt / Event ──────────────────────────────
def button_pressed(channel):
print(f"Button on GPIO{channel} pressed!")

GPIO.add_event_detect(27, GPIO.FALLING,
callback=button_pressed,
bouncetime=200)

# ── PWM ────────────────────────────────────────────
GPIO.setup(18, GPIO.OUT)
pwm = GPIO.PWM(18, 50)          # 50Hz (good for servos)
pwm.start(7.5)                  # Neutral position

# ── Cleanup ────────────────────────────────────────
GPIO.cleanup()

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Useful Tools & Commands

# Show GPIO status (requires raspi-gpio package)
raspi-gpio get

# Read a single pin's state
raspi-gpio get 17

# Set a pin high/low from the terminal
raspi-gpio set 17 op dh    # output, drive high
raspi-gpio set 17 op dl    # output, drive low

# Interactive pinout reference in the terminal
pinout

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Recommended Libraries

Library	Language	Install	Best For
RPi.GPIO	Python	pip install RPi.GPIO	General GPIO, beginners
gpiozero	Python	pip install gpiozero	High-level, readable API
pigpio	Python/C	sudo apt install pigpio	Precise PWM, remote GPIO
wiringPi	C/C++	sudo apt install wiringpi	C projects
lgpio	Python	pip install lgpio	Pi 5 recommended

💡 Pi 5 users: The Pi 5 uses a new GPIO chip (gpiochip4). Use lgpio or gpiozero — RPi.GPIO may not be fully compatible yet.

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Common Wiring Mistakes to Avoid

1. Connecting 5V directly to a GPIO pin — always use a logic level converter
2. Forgetting a resistor on an LED — will draw too much current and damage the pin
3. Not calling GPIO.cleanup() — leaves pins in undefined states
4. Confusing BCM and BOARD numbering — double-check before wiring
5. Powering the Pi from the 5V GPIO pin without protection — bypasses the polyfuse

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