ESP32 Pinout & GPIO Reference

Filterable ESP32 GPIO table with every trap flagged — strapping pins, ADC2-vs-WiFi, input-only pins and safe-pin list.

Filter pins

4, 13, 14, 16, 17, 18, 19, 21, 22, 23, 27, 32, 33

Fully safe GPIOs

GPIO 6–11

Never use (SPI flash)

GPIO	ADC	Touch	Flags	Notes
0	ADC2_1	T1	strapping, boot	Boot mode select — must be HIGH at reset to run; LOW enters flasher. Has pull-up; OK as button after boot.
1	—	—	tx	UART0 TX (console). Avoid for IO if you need serial logs.
2	ADC2_2	T2	strapping	Must be LOW/floating at reset to enter flasher. On-board LED on many dev kits.
3	—	—	rx	UART0 RX (console).
4	ADC2_0	T0	✓ safe	Safe general IO.
5	—	—	strapping	Outputs PWM at boot on some modules; VSPI CS default.
12	ADC2_5	T5	strapping, danger	MTDI — if HIGH at reset, flash voltage set to 1.8 V and boot FAILS on 3.3 V modules. Don't pull high.
13	ADC2_4	T4	✓ safe	Safe general IO (MTCK).
14	ADC2_6	T6	✓ safe	Outputs PWM briefly at boot (MTMS).
15	ADC2_3	T3	strapping	Silences boot log if LOW at reset (MTDO).
16	—	—	✓ safe	Safe IO — NOT available on WROVER (used by PSRAM).
17	—	—	✓ safe	Safe IO — NOT available on WROVER (PSRAM).
18	—	—	✓ safe	VSPI SCK default. Safe.
19	—	—	✓ safe	VSPI MISO default. Safe.
21	—	—	✓ safe	I²C SDA default. Safe.
22	—	—	✓ safe	I²C SCL default. Safe.
23	—	—	✓ safe	VSPI MOSI default. Safe.
25	ADC2_8	—	dac	DAC1 — true 8-bit analog out.
26	ADC2_9	—	dac	DAC2 — true 8-bit analog out.
27	ADC2_7	T7	✓ safe	Safe general IO.
32	ADC1_4	T9	✓ safe	ADC1 — usable WITH WiFi. RTC-capable (deep-sleep wake).
33	ADC1_5	T8	✓ safe	ADC1 — usable with WiFi. RTC-capable.
34	ADC1_6	—	input-only	Input only, no pull-ups. Good for analog.
35	ADC1_7	—	input-only	Input only, no pull-ups.
36	ADC1_0	—	input-only	SVP. Input only. Best ADC pin.
39	ADC1_3	—	input-only	SVN. Input only.

ADC2 unusable while WiFi is active — use ADC1 (GPIO 32–39) for WiFi projects

References: Espressif ESP32 Series Datasheet v4.x · ESP32 Technical Reference Manual (IO MUX/GPIO matrix)

The four classic ESP32 traps: (1) GPIO 6–11 talk to the SPI flash — touching them crashes everything; (2) ADC2 dies when WiFi is on; (3) strapping pins 0/2/5/12/15 must be in the right state AT RESET — a pull-down on 12 has bricked countless boards into 1.8 V flash mode; (4) 34–39 are input-only with no internal pulls. The GPIO matrix means any peripheral can route to almost any (output-capable) pin — pin choice is about boot states, not features.

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ESP32 Pinout Reference computes every ESP32 GPIO's capabilities and traps in a filterable table — free, instant and private in your browser. ESP32 developers choosing pins that won't fight the boot ROM use it to skip the datasheet algebra: type your numbers, read the answer with the substituted formula shown step by step, and share an exact permalink of the calculation.

About ESP32 Pinout & GPIO Reference

ESP32 Pinout Reference computes every ESP32 GPIO's capabilities and traps in a filterable table using the standard engineering relation: safe pins 4,13,16–23,25–27,32,33; input-only 34–39; never touch 6–11 (flash). Worked live: pulling GPIO12 high at reset switches flash to 1.8 V and bricks boot on most modules. The result recalculates on every keystroke, the worked-example panel shows your numbers substituted into the formula, and the Copy permalink button encodes the inputs in the URL so a colleague opens exactly your calculation. Everything runs client-side — nothing you type leaves your device.

How to use ESP32 Pinout & GPIO Reference

1Enter your values — the tool starts with realistic defaults for this exact use case, so the worked example is meaningful immediately.
2Read the live result and the worked-example panel, which substitutes your numbers into the formula step by step.
3Adjust any input to compare scenarios, then use Copy result or Copy permalink to share the calculation.

Why use ESP32 Pinout & GPIO Reference?

✓Implements the real formula — safe pins 4,13,16–23,25–27,32,33 — with the substitution shown, not a black box
✓Built for ESP32 developers choosing pins that won't fight the boot ROM
✓Copy result and permalink buttons — share the exact calculation in a README, forum answer or design review
✓100% free, no sign-up, runs entirely in your browser (works offline once loaded)

Frequently asked questions

How do you calculate esp32 pinout?+

Every ESP32 GPIO's capabilities and traps in a filterable table follows safe pins 4,13,16–23,25–27,32,33; input-only 34–39; never touch 6–11 (flash). For example, pulling GPIO12 high at reset switches flash to 1.8 V and bricks boot on most modules. The calculator applies the same relation and shows the substituted arithmetic so you can verify every step.

Why does my ESP32 ADC stop working when WiFi is on?+

You're on ADC2 — the WiFi driver owns it whenever the radio is active. Move analog inputs to ADC1 (GPIO 32–39). This single fact explains a large share of 'ESP32 ADC is broken' forum threads.

Which ESP32 pins are safe for relays/outputs at boot?+

Pins that don't glitch or carry strapping meaning: 4, 13, 16–23, 25–27, 32, 33. GPIO 0/2/5/12/15 have boot roles, 1/3 are the console, and 14/5 emit brief PWM at reset on some modules — a relay on those clicks at every power-up.

Is the ESP32 Pinout Reference free and private?+

Yes — completely free with no sign-up or usage limits, and it runs entirely in your browser: the values you enter are never uploaded or stored on a server.

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