What does N16R8 mean on the ESP32-S3-WROOM-1?

16 MB of Quad SPI flash and 8 MB of Octal SPI PSRAM. Espressif's ordering table rates R8 modules for −40 to 65 °C ambient.

Which pins does the N16R8's PSRAM use?

IO35, IO36 and IO37 (pads 28, 29 and 30). On modules with octal PSRAM they connect to the PSRAM and are not available for other uses.

What are the ESP32-S3 strapping pins?

GPIO0, GPIO3, GPIO45 and GPIO46. At reset GPIO0 has a weak pull-up, GPIO45 and GPIO46 weak pull-downs, and GPIO3 floats. GPIO0 and GPIO46 low together enter download mode.

Which ESP32-S3 pins are SDA and SCL?

There are no fixed ones: the GPIO matrix can route I²C to any free GPIO. The Arduino core's defaults are SDA on GPIO8 and SCL on GPIO9, which are pads 12 and 17 on the WROOM-1.

Why does my N16R8 not find its PSRAM?

Check the PSRAM type the firmware was built for. The N16R8's PSRAM is octal, so a build set for quad PSRAM cannot use it: select Octal in ESP-IDF's CONFIG_SPIRAM_MODE and rebuild.

ESP32-S3-WROOM-1 Pinout (N16R8)

ESP32-S3-WROOM-1 · ESP32-S3-WROOM-1 module, 18 × 25.5 × 3.1 mm

The ESP32-S3-WROOM-1 brings 36 GPIOs out to 41 pads. On the N16R8, three of them belong to the octal PSRAM, four are strapping pins, and two carry the native USB.

Checked against the KiCad library and datasheet on 4 November 2026

ESP32-S3-WROOM-1 pinout: KiCad footprint RF_Module:ESP32-S3-WROOM-1 seen from the top, beside the KiCad library symbol RF_Module:ESP32-S3-WROOM-1 with every pin number and name — The WROOM-1 footprint: pads 1 to 14 down the left, 15 to 26 along the bottom, 27 to 40 up the right, the ground pad (41) in the middle, and the antenna area at the top. KiCad's symbol already marks IO35 to IO37 as PSRAM. Exported from the KiCad 9 libraries (RF_Module:ESP32-S3-WROOM-1, RF_Module:ESP32-S3-WROOM-1). Open full size

Pin by pin

Pin	Name	Function
1	GND	Ground
2	3V3	Supply, 3.0 to 3.6 V. The supply must deliver at least 0.5 A
3	EN	High enables the chip, low powers it off. Never leave it floating
4	IO4	GPIO4, TOUCH4, ADC1_CH3
5	IO5	GPIO5, TOUCH5, ADC1_CH4
6	IO6	GPIO6, TOUCH6, ADC1_CH5
7	IO7	GPIO7, TOUCH7, ADC1_CH6
8	IO15	GPIO15, U0RTS, ADC2_CH4, XTAL_32K_P
9	IO16	GPIO16, U0CTS, ADC2_CH5, XTAL_32K_N
10	IO17	GPIO17, U1TXD, ADC2_CH6
11	IO18	GPIO18, U1RXD, ADC2_CH7, CLK_OUT3
12	IO8	GPIO8, TOUCH8, ADC1_CH7. SDA in the Arduino core
13	IO19	USB D− (native USB Serial/JTAG and USB OTG), GPIO19, U1RTS, ADC2_CH8
14	IO20	USB D+ (native USB Serial/JTAG and USB OTG), GPIO20, U1CTS, ADC2_CH9
15	IO3	Strapping: JTAG source, ignored unless an eFuse is burnt. No internal pull. TOUCH3, ADC1_CH2
16	IO46	Strapping: boot mode and ROM log. Weak pull-down
17	IO9	GPIO9, TOUCH9, ADC1_CH8, FSPIHD. SCL in the Arduino core
18	IO10	GPIO10, TOUCH10, ADC1_CH9, FSPICS0. SS in the Arduino core
19	IO11	GPIO11, TOUCH11, ADC2_CH0, FSPID. MOSI in the Arduino core
20	IO12	GPIO12, TOUCH12, ADC2_CH1, FSPICLK. SCK in the Arduino core
21	IO13	GPIO13, TOUCH13, ADC2_CH2, FSPIQ. MISO in the Arduino core
22	IO14	GPIO14, TOUCH14, ADC2_CH3, FSPIWP
23	IO21	GPIO21
24	IO47	GPIO47, SPICLK_P_DIFF. 1.8 V I/O on the N16R16VA only
25	IO48	GPIO48, SPICLK_N_DIFF. 1.8 V I/O on the N16R16VA only
26	IO45	Strapping: flash supply voltage (VDD_SPI). Weak pull-down; keep it low at reset
27	IO0	Strapping: boot mode. Weak pull-up; low at reset (with IO46 low) enters download mode
28	IO35	Taken by the octal PSRAM on N16R8 (and every R8/R16V module). GPIO35 on modules without it
29	IO36	Taken by the octal PSRAM on N16R8 (and every R8/R16V module). GPIO36 on modules without it
30	IO37	Taken by the octal PSRAM on N16R8 (and every R8/R16V module). GPIO37 on modules without it
31	IO38	GPIO38, FSPIWP
32	IO39	GPIO39, MTCK (JTAG), CLK_OUT3
33	IO40	GPIO40, MTDO (JTAG), CLK_OUT2
34	IO41	GPIO41, MTDI (JTAG), CLK_OUT1
35	IO42	GPIO42, MTMS (JTAG)
36	RXD0	U0RXD, GPIO44. The UART0 used for flashing and the boot log
37	TXD0	U0TXD, GPIO43. The UART0 used for flashing and the boot log
38	IO2	GPIO2, TOUCH2, ADC1_CH1
39	IO1	GPIO1, TOUCH1, ADC1_CH0
40	GND	Ground
41	EPAD	Ground, under the module. Soldering it is optional and improves cooling

Things that catch people out

N16R8 means 16 MB of Quad SPI flash and 8 MB of Octal SPI PSRAM. The octal PSRAM takes IO35, IO36 and IO37 (pads 28 to 30), so those three are not available for anything else.
GPIO26 to GPIO34 are not on the pads; GPIO26 to GPIO32 connect to the flash and PSRAM inside the package. Of the 36 GPIOs on the pads, the N16R8 leaves 33.
The firmware must be set for octal PSRAM. In ESP-IDF that is CONFIG_SPIRAM_MODE (Quad or Octal) under SPI RAM config. Octal PSRAM runs only in DTR mode, and the quad flash only in STR mode.
Download mode needs IO0 low and IO46 low at reset. Both have weak pulls (IO0 up, IO46 down) that give a normal boot when nothing drives them.
IO45 high at reset selects a 1.8 V flash supply. Every WROOM-1 except the N16R16VA runs its flash from 3.3 V, so keep IO45 low until the chip has booted.
The strapping pins are read when EN goes high, and the datasheet asks for them to hold their level for at least 3 ms after that.
R8 modules such as the N16R8 are rated for −40 to 65 °C ambient. Turning on PSRAM ECC raises that to 85 °C and costs 1/16 of the PSRAM.

Putting the ESP32-S3-WROOM-1 on a PCB

Feed 3V3 from a supply that can deliver 0.5 A, with 22 µF and 0.1 µF at the module, as in Espressif's peripheral schematic.
Put an RC delay on EN, usually 10 kΩ to 3V3 and 1 µF to ground, so the chip starts after its supply has settled. Add a reset button from EN to ground and a boot button or jumper from IO0 to ground.
For native USB, run IO19 (D−) and IO20 (D+) as a pair to the USB connector and keep other parts off those two pins. A USB-C receptacle also needs its own 5.1 kΩ resistor on CC1 and on CC2.
Put the antenna end at the edge of the board, and keep copper, parts and ground pour out from under it. The WROOM-1U uses an external antenna connector and has no keep-out.
The ground pad (41) is optional, but soldering it helps with heat. Do not over-paste it, or the module sits too high for the edge pads to wet.

Designing a board around it? Read ESP32 PCB design: antenna, power, boot pins and USB.

Common questions

What does N16R8 mean on the ESP32-S3-WROOM-1?: 16 MB of Quad SPI flash and 8 MB of Octal SPI PSRAM. Espressif's ordering table rates R8 modules for −40 to 65 °C ambient.
Which pins does the N16R8's PSRAM use?: IO35, IO36 and IO37 (pads 28, 29 and 30). On modules with octal PSRAM they connect to the PSRAM and are not available for other uses.
What are the ESP32-S3 strapping pins?: GPIO0, GPIO3, GPIO45 and GPIO46. At reset GPIO0 has a weak pull-up, GPIO45 and GPIO46 weak pull-downs, and GPIO3 floats. GPIO0 and GPIO46 low together enter download mode.
Which ESP32-S3 pins are SDA and SCL?: There are no fixed ones: the GPIO matrix can route I²C to any free GPIO. The Arduino core's defaults are SDA on GPIO8 and SCL on GPIO9, which are pads 12 and 17 on the WROOM-1.
Why does my N16R8 not find its PSRAM?: Check the PSRAM type the firmware was built for. The N16R8's PSRAM is octal, so a build set for quad PSRAM cannot use it: select Octal in ESP-IDF's CONFIG_SPIRAM_MODE and rebuild.

Describe the board, say an ESP32-S3-WROOM-1 N16R8 with USB-C and an I²C sensor. When PCBEditor assigns the pins, it keeps peripherals off the strapping pins, the USB pair and IO35 to IO37.

Design an ESP32-S3 board →

Sources

Espressif ESP32-S3-WROOM-1 & WROOM-1U datasheet v1.8
Espressif ESP32-S3 Series datasheet v2.2 (GPIO restrictions, strapping pins)
ESP-IDF: SPI flash and external SPI RAM configuration (ESP32-S3)
arduino-esp32: ESP32-S3 default pins (variants/esp32s3/pins_arduino.h)
KiCad 9 libraries: symbol RF_Module:ESP32-S3-WROOM-1, footprint RF_Module:ESP32-S3-WROOM-1 (CC-BY-SA 4.0).