Which i2c connector for my project?
Two quick questions about voltage and what matters most, and you'll get a recommended standard with the reasoning — not just a name.
What voltage is your project?
What matters most?
STEMMA QT is the safe default: the huge JST-SH ecosystem, cross-compatible with Qwiic, and it tolerates both 3.3 V and 5 V.
The reasoning behind it
What separates the i2c connector ecosystems
i2c never specified a connector — the spec stops at two wires, addressing and timing. So every maker company invented its own, and the choice comes down to three trade-offs rather than one being "best".
Size versus fingers. Qwiic and STEMMA QT use a 1 mm JST-SH — tiny, which is perfect on a crowded board and genuinely fiddly to plug in repeatedly. Grove is 2 mm and almost impossible to get wrong, at the cost of real estate. STEMMA classic (JST-PH) sits between them.
Voltage convention. Qwiic and STEMMA QT standardised on 3.3 V, which is what makes them safe to mix casually — everything on the chain agrees. Ecosystems that tolerate both rails give you flexibility and hand you the job of checking each board, since level shifting is on you when the host disagrees.
Ecosystem size. The connector is only worth as much as the boards that ship with it — worth checking the board dataset for the parts you actually need before committing.
Already have hardware and just need them to talk? That's the other direction — the compatibility checker or the pre-answered pairing pages. Whatever you pick, it's the same bus underneath: same addresses, same pull-ups, same limits.