Arduino Nano Pinout
Arduino Nano (classic, ATmega328P), 30 pins, top view with the USB socket at the bottom. Check your board against its silkscreen before wiring power.
A6 and A7 are analog only
They wire straight to the ADC and cannot be digital inputs or outputs. Every other analog pin doubles as a digital one.
Power paths
VIN feeds the onboard regulator (7 to 12 V), the 5V pin bypasses it, and 3V3 comes from the USB interface chip with only about 50 mA to give. Logic is 5 V, so 3.3 V sensors need a level shifter.
Buses and PWM
I2C lives on A4 and A5, SPI on D11 to D13 with D10 as chip select, and the pins tagged PWM above are the analogWrite-capable ones.
Sources and datasheets
This diagram was cross-checked against the manufacturer documentation below plus at least two independent references before publishing. When they disagreed, the manufacturer won.
More boards and plugs live on the pinouts index.