ESP32 pinout and pin diagram

ESP32 development boards bring out most of the chip’s GPIO, but not every pin is free to use. GPIO6 to 11 belong to the on-board flash, GPIO34 to 39 are input-only, and five strapping pins (0, 2, 5, 12, 15) are read at reset to choose the boot mode, so wiring them carelessly can stop the board from starting.

The first tab of the pin diagram is Espressif’s official 38-pin ESP32-DevKitC V4. The second is the widely sold 30-pin “DOIT DevKit V1” layout, which Espressif doesn’t publish; clones vary, so check the silkscreen on your board. Tap any pin to see all of its functions.

How to read the ESP32 pin diagram

An ESP32 pin diagram shows two kinds of label. The GPIO number (GPIO23, for example) is the chip’s own name for the pin and is what your code uses: pinMode(23, OUTPUT) in Arduino, GPIO_NUM_23 in ESP-IDF. The silkscreen label printed on the board varies by maker: Espressif’s DevKitC prints IO23, the DOIT board prints D23, and the flash pins carry their bus names (CLK, SD0, CMD). The ESP32 chip has 34 GPIO, of which 32 reach the pins of the WROOM-32 module on these boards (GPIO37 and 38 stay inside). The 38-pin DevKitC brings out all 32; the 30-pin DOIT board brings out 25 and leaves the flash pins off.

Four pins are not GPIO at all:

• 3V3: the 3.3 V rail from the on-board regulator. It can also feed the board from a regulated 3.3 V supply.
• 5V on the DevKitC, VIN on the DOIT board: the input to the 3.3 V regulator, about 5 V. It is the same rail that USB power feeds, so don’t use both at once.
• GND: several, all common.
• EN: chip enable. Pulled high to run; the EN button pulls it low to reset the chip.

Which ESP32 pins are safe to use?

15 pins are free for any job: 4, 13, 14, 16, 17, 18, 19, 21, 22, 23, 25, 26, 27, 32, 33. Four more, 34, 35, 36, 39, are good inputs, especially for analog sensors, but cannot drive anything. The five strapping pins (0, 2, 5, 12, 15) work as normal GPIO after boot, as long as nothing connected to them forces the wrong level at reset. GPIO1 and GPIO3 are the serial port you flash through, and GPIO6 to GPIO11 belong to the flash chip. The full list, from the chip’s datasheet and Espressif’s DevKitC guide:

ESP32 ADC pins: ADC1 vs ADC2

The ESP32 has two 12-bit analog-to-digital converters with 16 channels between them. ADC1 is always available. ADC2 is shared with the Wi-Fi driver and cannot be read while Wi-Fi is on, which is the usual reason an analog sensor reads nothing in a Wi-Fi project. Put analog inputs on ADC1.

The input range depends on the attenuation setting. At the highest setting the calibrated useful range is roughly 150 to 2,450 mV, and accuracy falls off towards both ends, so scale a sensor to sit in the middle. Chips differ by several percent before calibration; use the calibrated millivolt functions rather than raw counts when the number matters.

Touch, DAC and PWM pins

• Capacitive touch: T0 on GPIO4, T1 on GPIO0, T2 on GPIO2, T3 on GPIO15, T4 on GPIO13, T5 on GPIO12, T6 on GPIO14, T7 on GPIO27, T8 on GPIO33, T9 on GPIO32. A wire or a copper pad on the pin becomes a touch button.
• DAC: two 8-bit outputs, DAC1 on GPIO25 and DAC2 on GPIO26, for a true analog voltage between 0 and 3.3 V.
• PWM: the LED PWM controller (LEDC) has 16 channels and can drive any output-capable pin, so every pin in the “free” list can dim an LED or drive a servo.
• Deep sleep wake-up: only RTC GPIO keep working in deep sleep: 0, 2, 4, 12, 13, 14, 15, 25, 26, 27, 32, 33, 34, 35, 36, 39.

I2C, SPI and UART pins

The ESP32’s GPIO matrix can route most peripherals to almost any pin, so these are defaults, not limits. Using them keeps libraries and wiring diagrams simple:

Strapping pins and boot modes

At reset the ESP32 samples five strapping pins to decide how to start. Each has an internal pull resistor that sets the normal level, so the board boots correctly when nothing is connected. Trouble starts when a sensor, a pull resistor or an LED on one of these pins holds it at the wrong level during power-up.

The one that catches most people is GPIO12: pulled high at power-up, it switches the flash supply to 1.8 V and a board with 3.3 V flash will not boot. If an upload fails with the board stuck in a reset loop, disconnect whatever is on GPIO12, GPIO0, GPIO2, GPIO5 and GPIO15 and try again. To enter the bootloader by hand, hold BOOT (GPIO0 low), tap EN, then release BOOT.

Powering an ESP32 board

Use one source at a time: USB, the 5V/VIN pin with about 5 V, or the 3V3 pin with a regulated 3.3 V. Wi-Fi transmit bursts draw a few hundred milliamps for short periods, so a weak supply or a long thin USB cable causes brownout resets that look like software crashes. A supply rated for 500 mA or more, and a capacitor of a few hundred microfarads near the board on battery projects, keeps it stable.

Driving LEDs, relays and 5 V signals

• LEDs. A red LED with a 2 V forward drop at 10 mA from a 3.3 V pin needs (3.3 − 2) ÷ 0.01 = 130 Ω; the next standard value up, 150 Ω, gives 8.7 mA. The LED resistor calculator handles other colours and supplies.
• Current limits. Most pins can source about 40 mA at full drive strength and sink about 28 mA, with an absolute maximum of 1,200 mA for all I/O together. Keep each pin to a few milliamps and drive relays, motors and LED strips through a transistor or MOSFET.
• 5 V signals. The pins are not 5 V tolerant. A divider of 1.8 kΩ over 3.3 kΩ turns a 5 V signal into 3.24 V and draws 0.98 mA; check other values with the voltage divider calculator. Fast or bidirectional buses need a proper level shifter.

ESP32 DevKitC vs the 30-pin DOIT board

Both run the same chip, so code is interchangeable; only the physical positions differ. Compare the silkscreen on your board with the diagram before wiring, because 36- and 38-pin clones of the DOIT layout also exist.

Common ESP32 wiring mistakes

• Wiring an output to GPIO34 to 39 and wondering why nothing happens: they are input-only.
• Expecting a pull-up on GPIO34 to 39 for a button: add an external resistor.
• Reading an analog sensor on an ADC2 pin while Wi-Fi is on.
• A pull-up or a sensor holding GPIO12 high, so the board will not boot.
• Connecting anything to GPIO6 to 11 on the DevKitC.
• Feeding 5 V signals straight into a pin, or powering the board from USB and the 5V pin at the same time.

Key facts

• All ESP32 GPIO run at 3.3 V and are not 5 V tolerant: an input must stay below the I/O supply + 0.3 V. Use a level shifter for 5 V signals.
• Input-only pins: GPIO34, 35, 36 (VP) and 39 (VN). They cannot drive outputs and have no internal pull-up or pull-down resistors.
• GPIO6-11 (labelled CLK, SD0-SD3/D0-D3, CMD) connect to the module's SPI flash - never use them. On WROVER modules with PSRAM, GPIO16 and 17 are also taken.
• Strapping pins are read at reset, then become ordinary GPIO: GPIO0 (internal pull-up), GPIO2 (pull-down), GPIO5 (pull-up), GPIO12/MTDI (pull-down), GPIO15/MTDO (pull-up). Do not let external circuits force them to the wrong level during power-up.
• Boot modes: GPIO0 high = run from flash; GPIO0 low with GPIO2 low or floating = serial download (the BOOT button pulls GPIO0 low).
• GPIO12 (MTDI) high at reset switches the flash supply to 1.8 V, which stops boards with 3.3 V flash (most WROOM-based kits) from booting. GPIO15 (MTDO) low at reset silences the ROM boot log on TX0; GPIO15 and GPIO5 together set SDIO-slave timing.
• ADC: two 12-bit SAR converters, 18 channels. ADC1 is on GPIO32-39; ADC2 is on GPIO0, 2, 4, 12-15 and 25-27. ADC2 cannot be used while Wi-Fi is running - put analog sensors on ADC1 pins in Wi-Fi projects.
• The ADC range depends on attenuation; at the highest setting the calibrated useful range is about 150-2450 mV, and readings get less accurate toward the ends. Chips differ by about ±6 % before calibration.
• DAC: two 8-bit outputs, DAC1 on GPIO25 and DAC2 on GPIO26.
• Capacitive touch: T0 GPIO4, T1 GPIO0, T2 GPIO2, T3 GPIO15, T4 GPIO13, T5 GPIO12, T6 GPIO14, T7 GPIO27, T8 GPIO33, T9 GPIO32.
• UART0 (GPIO1 TX0, GPIO3 RX0) is wired to the USB-serial bridge for flashing and the console. UART2's native pins are GPIO16 (RX2) and GPIO17 (TX2); note that Arduino-ESP32 core 3.x defaults Serial2 to GPIO4/GPIO25 and Serial1 to GPIO26/GPIO27 unless you pass pins to begin().
• Default buses in the Arduino core: I2C SDA GPIO21, SCL GPIO22; SPI (VSPI) MOSI 23, MISO 19, SCK 18, SS 5. The second SPI (HSPI) native pins are MOSI 13, MISO 12, SCK 14, SS 15. The GPIO matrix can route most peripherals to almost any pin.
• JTAG: GPIO12 TDI, GPIO13 TCK, GPIO14 TMS, GPIO15 TDO.
• Pins usable in deep sleep (RTC GPIO): 0, 2, 4, 12-15, 25-27, 32-39.
• Drive capability at maximum drive strength: about 40 mA source per pin on most pins (about 20 mA on VDD_SDIO-domain pins), about 28 mA sink; the per-pin figure drops toward 29 mA as more pins source current at once. Absolute-maximum total for all I/O: 1200 mA. Internal pull resistors are about 45 kΩ.
• EN is the chip-enable/reset line (CHIP_PU): high = running. Dev kits pull it up and connect it to the EN button.
• ESP32-DevKitC V4 power: use exactly one source - micro-USB, the 5V pin, or the 3V3 pin. Feeding two at once can damage the board or the supply.
• ESP32-DevKitC V4 is Espressif's reference board (header pinout published by Espressif). The 30-pin 'ESP32 DEVKIT V1 / DOIT' layout comes from third-party makers; its common pin order is shown here, but clones vary, and it has VIN instead of a 5V pin and no flash pins broken out.
• Most DOIT-style boards have a blue LED on GPIO2 (Arduino LED_BUILTIN = 2) - remember GPIO2 is also a strapping pin.
• GPIO32 and GPIO33 can host an external 32.768 kHz crystal for the RTC.

Sources

Pin assignments were checked against these references on 2026-10-14. The diagram is our own drawing.

• Espressif - ESP32-DevKitC V4 User Guide (esp-dev-kits)
• Espressif - ESP32-DevKitC pin layout figure (esp32_devkitC_v4_pinlayout.png)
• Espressif - ESP32 Series Datasheet v5.3
• Espressif - ESP-IDF Programming Guide: GPIO & RTC GPIO (ESP32)
• Espressif arduino-esp32 core - variants/esp32 and variants/doitESP32devkitV1 pins_arduino.h
• Espressif arduino-esp32 core - cores/esp32/HardwareSerial.h (3.x) and HardwareSerial.cpp (2.0.x)
• Wokwi elements - esp32-devkit-v1-element.ts
• Mischianti - DOIT ESP32 DEV KIT v1 high resolution pinout and specs