i2c connector standards
An i2c connector is a keyed, solderless plug that carries the i2c bus — power, ground, SDA (data) and SCL (clock) — from one board to the next. i2c itself defines no connector, so makers each built their own; these are the 6 you'll actually meet, side by side.
In one line
What is an i2c connector?
An i2c connector is a standardised 4-pin plug that carries the four signals every i2c device needs — power, ground, SDA and SCL — on a keyed, solderless cable, so you can chain boards without wiring each one by hand. Because the i2c specification covers only the protocol and never a physical connector, hardware makers created their own: Qwiic, STEMMA QT, Grove, Gravity, Breakout Garden and STEMMA. They carry the identical bus underneath — the differences are pin pitch, pin order and logic voltage.
| Standard | Connector | Logic |
|---|---|---|
| Qwiic SparkFun | JST-SH · 4-pin · 1 mm | 3v3 |
| STEMMA QT Adafruit | JST-SH · 4-pin · 1 mm | 3v3-5v |
| STEMMA (classic) Adafruit | JST-PH · 4-pin · 2 mm | 3v3-5v |
| Grove Seeed Studio | Grove 4-pin · 4-pin · 2 mm | varies |
| Breakout Garden Pimoroni | 5-pin edge · 5-pin · 2.54 mm | 3v3 |
| Gravity DFRobot | Gravity 4-pin · 4-pin · 2 mm | varies |
The short version
Why there are six standards for one bus
i2c itself never specified a connector. The spec covers two wires, addressing and timing — it says nothing about how you physically join one board to the next. So every maker company filled that gap themselves, and each one optimised for something different: Qwiic (SparkFun) and STEMMA QT (Adafruit) went small with a 1 mm JST-SH and standardised on 3.3 V; Grove (Seeed) went large and beginner-proof at 2 mm; STEMMA classic sits between them on JST-PH; Breakout Garden (Pimoroni) skipped cables entirely for an edge connector; and Gravity (DFRobot) kept the colour-coded 4-pin style.
The good news: Qwiic and STEMMA QT are the same connector with the same pin order, so those two interchange freely — that's one ecosystem in practice, not two. The rest need an adapter, and sometimes a level shifter. Every combination is worked out in the compatibility pairings, or answer it interactively with the compatibility checker.
Underneath the plug, it's all the same bus: the same 7-bit addresses, the same pull-up resistors, the same 400 pF capacitance budget. A connector standard buys you convenience and a voltage convention — never a different protocol. New to all this? Start with what i2c is, or see which connector suits your project.