Pull-Up Resistor Calculator

About this calculator

In digital logic, a pull-up resistor connects a signal line to the supply voltage so it reads a stable HIGH when nothing is actively driving it, and drops LOW when a device (like an open-drain output or a switch to ground) sinks current through it. This calculator finds the minimum resistor value that still guarantees a valid logic-low voltage given the supply voltage, the driving device's rated output-low voltage, and its maximum sink current — plus the power the resistor dissipates at that current.

Electronics and firmware engineers size pull-ups constantly when working with I2C buses, open-drain GPIO pins, push-button inputs, and reset lines: too large a resistor slows signal transitions and makes the line noise-prone, while too small a value wastes power and can exceed the sinking device's current rating. Getting the value right is a routine step in schematic design for microcontroller and embedded systems boards.