i2c address list

The basics

What is an i2c address?

Every chip on an i2c bus answers to its own 7-bit address. The controller opens each transaction by broadcasting an address on SDA; the one device that recognises it acknowledges and replies, while every other device ignores the rest of the exchange. That single mechanism is what lets one pair of wires — SDA and SCL — carry a temperature sensor, an OLED display, a real-time clock and a GPIO expander simultaneously.

Because the address is only 7 bits, the raw space runs 0x00–0x7F (128 slots). The spec carves reserved blocks off both ends, leaving 0x08–0x77 — 112 usable i2c addresses. In practice you'll see the same few dozen over and over, because chip vendors pick from a small pool — which is exactly why address collisions are the most common i2c roadblock.

The classic trap

7-bit vs 8-bit: why 0x76 shows up as 0xEC

This single confusion accounts for a huge share of "my i2c address is wrong" posts. An i2c transaction actually puts eight bits on the wire: the 7-bit address, then one read/write bit. Some datasheets document the address as that whole byte — the 8-bit form — while libraries and scanners use the 7-bit form.

The conversion is a single shift. A BME280 at 7-bit 0x76 appears as 0xEC when writing (0x76 << 1) and 0xED when reading (the same byte with the read bit set). All three numbers describe the same chip.

The rule of thumb: if a documented address is roughly double what your scanner reports, you're looking at the 8-bit form — shift it right one bit and move on. Every address on this page is the 7-bit form, matching what i2cdetect and the Arduino Wire library expect.

Find yours

How to find an i2c device's address

Don't guess — scan. The bus tells you exactly who's home in about a second:

# Raspberry Pi / any Linux box
sudo apt install i2c-tools
i2cdetect -y 1

On Arduino, ESP32 or a Pico, run a scanner sketch instead — the bus scanning guide has ready-to-paste code for Arduino, MicroPython and the Pi, plus how to read the output. Our free i2c tool goes a step further: it scans, then reads each chip's WHO_AM_I register to name the actual silicon — telling a BME280 from a BMP280, or a genuine HMC5883L from the QMC5883L clone.

An empty scan is a wiring problem, not an addressing one: work the 7-step troubleshooting checklist, and check that pull-up resistors are present.