I2C Pull-up Resistor (3.3V)

Need a quick 3.3V I2C pull-up estimate? Use this guide, then run the full calculator for exact range.

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Use the full I2C tool to calculate Rmin/Rmax from current and timing limits.

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Typical 3.3V starting points

100 kHz, short bus: often around 4.7kΩ

400 kHz, moderate bus cap: often 2.2kΩ to 4.7kΩ

Higher capacitance: usually requires lower resistor value

Why values vary

Pull-up value depends on sink current capability and total bus capacitance. The same board voltage can still need different resistors for different cable lengths, devices, and speed modes.

FAQ

Can I always use 4.7kΩ at 3.3V?

No. It is a common starting value, but timing/current limits may require different resistor values.

Do I need separate pull-ups on SDA and SCL?

Yes, each line typically needs its own pull-up resistor.