ESP32 Safe GPIO Pins: Which Pins You Can (and Can't) Use

📅 July 4, 2026 ✍️ Devender Gupta 📁 Guides

One of the most confusing aspects of the ESP32 for beginners is understanding which GPIO pins are safe to use. Unlike an Arduino Uno where nearly every pin works the same way, the ESP32 has strapping pins, input-only pins, flash-dedicated pins, and pins with Wi-Fi conflicts.

This guide categorizes every ESP32 GPIO pin by safety level so you can make the right choice for your project.

⚠️ Disclaimer Pin behavior can vary slightly between ESP32 board models (DevKit V1 vs NodeMCU-32S vs custom boards). Always verify with your board's schematic. This guide covers the standard ESP32-WROOM-32 module found on most development boards.

Pin Safety Categories

🟢 GREEN: Safe to Use

These pins are safe for any digital I/O, PWM, or peripheral function. No boot issues, no conflicts:

GPIO	Notes
GPIO13	Also ADC2_CH4, TOUCH4, HSPI_MOSI
GPIO14	Also ADC2_CH6, TOUCH6, HSPI_CLK
GPIO16	UART2 RX — safe for general use when not used as UART
GPIO17	UART2 TX — safe for general use when not used as UART
GPIO18	VSPI_CLK — safe for general use when not used as SPI
GPIO19	VSPI_MISO — safe for general use when not used as SPI
GPIO21	I2C_SDA — safe for general use when not used as I2C
GPIO22	I2C_SCL — safe for general use when not used as I2C
GPIO23	VSPI_MOSI — safe for general use when not used as SPI
GPIO25	Also DAC_1, ADC2_CH8
GPIO26	Also DAC_2, ADC2_CH9
GPIO27	Also ADC2_CH7, TOUCH7
GPIO32	ADC1_CH4, TOUCH9 — preferred for analog
GPIO33	ADC1_CH5, TOUCH8 — preferred for analog

🟡 YELLOW: Use with Caution

These pins work for general I/O but have restrictions you must be aware of:

GPIO	Restriction
GPIO0	Strapping pin. Must be HIGH for normal boot, LOW for flash mode. Use with external pull-up or avoid.
GPIO2	Strapping pin. Must be LOW/floating during flashing. Onboard LED on some boards.
GPIO4	ADC2_CH0 — unreliable when Wi-Fi is on. Strapping on some boards.
GPIO5	Strapping pin. Briefly toggles during boot on some boards.
GPIO12	Strapping pin (MTDI). If pulled HIGH, sets flash voltage to 1.8V — may prevent boot.
GPIO15	Strapping pin (MTDO). If pulled LOW, disables ROM boot messages.
GPIO1	UART0 TX — connected to USB-Serial. Avoid using for general I/O.
GPIO3	UART0 RX — connected to USB-Serial. Avoid using for general I/O.
GPIO34	Input-only. Cannot output digital HIGH/LOW. Great for ADC.
GPIO35	Input-only. Cannot output digital HIGH/LOW. Great for ADC.
GPIO36	Input-only (SENSOR_VP). ADC1_CH0. No output.
GPIO39	Input-only (SENSOR_VN). ADC1_CH3. No output.

🔴 RED: Do Not Use

These pins are connected to the internal SPI flash memory. Using them will crash your ESP32:

GPIO	Function
GPIO6	FLASH_CLK (SPI clock to flash memory)
GPIO7	FLASH_D0 (Flash data line 0)
GPIO8	FLASH_D1 (Flash data line 1)
GPIO9	FLASH_D2 (Flash data line 2)
GPIO10	FLASH_D3 (Flash data line 3)
GPIO11	FLASH_CMD (Flash command line)

🚫 GPIO6–GPIO11 are DEADLY These pins are physically connected to the ESP32's SPI flash memory on the module. Any digital I/O operation on these pins will cause a system crash or exception. Do not connect anything to them.

Quick Decision Flowchart

Use this decision tree to pick the right pin for your project:

Need analog input + Wi-Fi? → Use ADC1 pins (GPIO32–GPIO39)
Need analog input + no Wi-Fi? → Any ADC pin works (ADC1 or ADC2)
Need digital output (LED, relay)? → Use green GPIOs (13,14,16,17,18,19,21,22,23,25,26,27,32,33)
Need I2C? → GPIO21 (SDA) and GPIO22 (SCL) — or remap to any green pin
Need SPI? → VSPI: GPIO23 (MOSI), GPIO19 (MISO), GPIO18 (CLK), GPIO5 (CS)
Need UART? → UART2: GPIO16 (RX), GPIO17 (TX)
Need touch input? → GPIO0,2,4,12,13,14,15,27,32,33 (TOUCH0–9)
Beginner, first project? → Start with GPIO16, GPIO17, GPIO18, GPIO19, GPIO21, GPIO22, GPIO23

Beginner's Cheat Sheet

If you're just starting with ESP32, memorize these simple rules:

Avoid GPIO6–GPIO11 entirely (they connect to flash memory)
Avoid GPIO1 and GPIO3 (they are used for USB-Serial communication)
Use GPIO16, GPIO17, GPIO18, GPIO19, GPIO21, GPIO22, GPIO23 for your first projects
Use GPIO32 or GPIO33 for analog sensors (ADC1 — works with Wi-Fi)
If your project stops uploading: check if GPIO0, GPIO2, GPIO5, GPIO12, or GPIO15 is being pulled LOW or HIGH at boot

🔧 Find Safe Pins Visually

Our interactive ESP32 pinout tool color-codes every pin by safety level. Hover to see full details.

Open Interactive Pinout

Frequently Asked Questions

Which ESP32 pins are 5V tolerant?

None. ESP32 GPIO pins are 3.3V logic only. Applying 5V to any GPIO will damage the pin or the entire chip. Use a level shifter for 5V sensors and devices.

Can I use the flash pins if I have a custom board design?

GPIO6–GPIO11 are physically bonded to the flash memory on the ESP32-WROOM module. On a custom board using the bare ESP32 chip, these can be repurposed only if you use an external SPI flash on different pins — but this is extremely advanced and not recommended.

Why are some pins input-only?

GPIO34, GPIO35, GPIO36, and GPIO39 lack output drivers in the ESP32 silicon. They are designed as input-only pins primarily for ADC use. This is a hardware limitation, not a configuration setting.