Pull-up Resistor Calculator

Calculate general-purpose pull-up and pull-down resistor values. Consider input thresholds and load current.

Pull-upPull-downResistorGPIODigitalLogic

Calculator

Quick Presets

Supply Voltage (Vcc)

Max Low Voltage (Vol)

From datasheet (Vol max)

Sink Current (Iol)

From datasheet (Iol)

      Vcc
       │
      ┌┴┐
      │ │ R (Pull-up)
      └┬┘
       │
       ├──── Output
       │
      ─┴─
      ///  Open-drain/
           Open-collector

How to Use This Calculator

This pull-up resistor calculator helps you find the optimal resistor value for open-drain outputs, GPIO buttons, and other digital interfaces where a pull-up is required.

Select a Quick Preset — Choose from common configurations like 3.3V or 5V logic
Enter Supply Voltage (Vcc) — The voltage level your pull-up connects to
Enter Max Low Voltage (Vol) — Maximum voltage for a valid logic low (from datasheet)
Enter Sink Current (Iol) — Maximum current the output can sink while maintaining Vol
Click Calculate — Get the acceptable resistance range and standard values

Pull-up Resistor Formulas

R_max = (V_cc - V_ol) / I_ol

Maximum resistance to ensure valid logic low

Understanding the Limits

Maximum Resistance: If resistance is too high, the pull-up current won't be enough for the output to pull the line low below Vol
Minimum Resistance: Limited by power dissipation and maximum current draw. Typically 1kΩ or Vcc/20mA minimum
Sweet Spot: Usually 4.7kΩ to 10kΩ for 3.3V/5V logic provides a good balance

Common Applications

Application	Typical Value	Notes
Push Button	10kΩ	Low current draw, debounce with capacitor
Open-Drain Output	4.7kΩ - 10kΩ	Balance speed vs. power
I2C Bus	2.2kΩ - 10kΩ	Depends on bus capacitance, see I2C calculator
Reset Line	10kΩ	Often with 100nF capacitor for noise immunity
1-Wire Bus	4.7kΩ	Standard value per specification
Interrupt Input	10kΩ - 100kΩ	Low power, edge-triggered

Design Guidelines

Choosing Pull-up vs Pull-down

Pull-up: Default state is HIGH. Use for active-low signals, open-drain outputs
Pull-down: Default state is LOW. Use for active-high signals, unused inputs

Rise Time Considerations

The RC time constant affects signal rise time: τ = R × C_load. For faster edges, use lower resistance, but this increases power consumption when the line is pulled low.

Power Consumption

When the output is LOW: P = (V_cc - V_ol)² / R. For battery-powered applications, use higher resistance values and minimize time spent in the LOW state.

Frequently Asked Questions

Why do I need a pull-up resistor?

Open-drain/open-collector outputs can only pull a line LOW, they cannot drive it HIGH. A pull-up resistor provides the HIGH level when the output is not active. Similarly, floating inputs on microcontrollers can cause erratic behavior.

Can I use the internal pull-up on my microcontroller?

Yes, but internal pull-ups are typically weak (20-50kΩ). They work for low-speed applications like buttons but may be too slow for communication buses or may not meet Vol requirements with high sink currents.

What happens if my pull-up is too weak (high resistance)?

The output may not be able to pull the line low enough to register as a valid logic LOW. This can cause unreliable communication or false readings.

What happens if my pull-up is too strong (low resistance)?

More current flows when the line is pulled low, wasting power and potentially exceeding the output's sink current capability. This could damage the output stage.

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