Enter Divider Parameters
Set load resistance to zero for an open-circuit output calculation.
Example Data Table
| Source | R1 | R2 | Load | Loaded output | R1 power | R2 power |
|---|---|---|---|---|---|---|
| 12 V | 10 kΩ | 5 kΩ | Open | 4.000 V | 6.40 mW | 3.20 mW |
| 12 V | 10 kΩ | 5 kΩ | 10 kΩ | 3.000 V | 8.10 mW | 1.80 mW |
| 24 V | 22 kΩ | 10 kΩ | 100 kΩ | 7.237 V | 12.76 mW | 5.24 mW |
Formula Used
For an unloaded divider, the lower resistor receives a fraction of the source voltage.
When a load is connected, combine the lower resistor and load first.
Vout = Vs × Rlower / (Rs + R1 + Rlower)
Power uses P = I²R or P = V²/R. The tolerance range checks resistor and source corners.
How to Use This Calculator
- Enter the supply voltage and optional source resistance.
- Add R1 and R2 values with their units.
- Enter resistor tolerances and selected power ratings.
- Enter the real circuit load, or leave it at zero.
- Choose a practical power margin and calculate.
- Review loaded output, tolerance range, power, and notices.
- Download results after confirming the design assumptions.
Voltage Divider Design Essentials
Understanding Divider Voltage
A voltage divider uses two resistors in series. The source voltage appears across both resistors. The output is taken from the lower resistor. This simple network creates a smaller reference voltage. The basic calculation assumes no external load. In that condition, resistor current is identical through both parts. The resistor ratio decides the output fraction. A larger lower resistor produces a larger output. A larger upper resistor produces a smaller output. The source voltage sets the available range. Resistor values affect current and wasted power. They do not change the ideal ratio when scaled equally.
Why Loading Matters
A connected circuit can change the result. The load resistor sits in parallel with the lower divider resistor. Their combined resistance becomes smaller than the original lower resistor. That reduction lowers the output voltage. A high input impedance load causes little error. A low input impedance load causes a noticeable error. This calculator shows both output values. It also reports loading error as a percentage. Compare them carefully before using the divider. Buffer amplifiers can isolate sensitive divider outputs. Alternatively, choose lower divider resistance values. That approach improves stiffness but increases current use and heat.
Power, Tolerance, and Ratings
Every resistor has a power limit. Divider current creates heat in both resistors. The upper resistor often dissipates more power when its resistance is higher. The calculator computes each dissipation value. It suggests a minimum rating with design margin. Never operate components continuously at their published maximum. Tolerance changes resistor values and alters output voltage. The worst case can matter in threshold circuits. Enter a tolerance percentage to estimate output limits. Use precision resistors where accuracy is essential. Check voltage ratings too, especially with high supply voltages. Power ratings alone do not guarantee safe operation.
Practical Design Checks
Start with output and supply. Select a convenient divider current. Calculate resistor values from the required ratio. Then add the real load resistance. Recheck the loaded output and error. Inspect current for battery-powered equipment. Inspect resistor power for warm or high-voltage circuits. Use the plot to see output changes across a source-voltage sweep. Export the results for a design note or review. This tool supports early design work and troubleshooting. It does not replace component datasheets, schematic review, or safety standards. De-energize equipment before measuring resistance. Use appropriate probes and protective practices around energized circuits.
Voltage Divider FAQs
1. What is a voltage divider?
A voltage divider is a series resistor network that produces a lower voltage at the connection between resistors. Its output depends on the resistor ratio, source voltage, source resistance, and any connected load.
2. Why is my measured output lower than expected?
A meter, sensor, or circuit input can load the divider. The load acts in parallel with the lower resistor. That lowers its equivalent resistance and reduces output voltage. Include the actual input resistance in the calculation.
3. Does resistor size change the ideal output ratio?
No. Scaling both resistor values by the same amount preserves the ideal ratio. It changes divider current, heat, noise sensitivity, loading resistance, and practical response to connected circuits.
4. What load resistance is considered safe?
There is no universal value. A load at least ten times the lower resistor usually reduces error, but precise designs may need much more. Review the loading error percentage for your actual accuracy target.
5. How do I calculate divider current?
With no load, divide source voltage by the series resistance. With a load, first combine the lower resistor and load in parallel. Then divide source voltage by source resistance plus the remaining series resistance.
6. What does Thevenin resistance mean here?
Thevenin resistance is the output resistance seen by a connected load. A smaller value makes the divider stiffer and reduces loading error. It also normally requires lower resistor values and higher divider current.
7. How are resistor tolerances applied?
The calculator checks combinations of minimum and maximum source, resistor, and optional load values. These corners estimate the possible output range. Real temperature effects and aging can add further variation.
8. Why check resistor power ratings?
Resistors convert electrical energy into heat. A rating check helps prevent overheating, drift, and failure. Use a safety margin because ambient temperature, enclosure conditions, and part derating affect usable power.
9. Can I use a divider to power a device?
Usually not. Divider voltage changes as device current changes. Use a regulator, reference, or buffer for a supply rail. A divider is better for low-current sensing, biasing, and reference signals.
10. What does source resistance do?
Source resistance adds series resistance before the divider. It reduces available voltage and changes output behavior under load. Batteries, signal generators, sensors, and upstream circuits can all contribute effective source resistance.
11. Is this calculator suitable for high-voltage circuits?
It can estimate electrical quantities, but it does not confirm safety. High-voltage work requires suitable component voltage ratings, creepage distances, insulation, measurement equipment, procedures, and qualified judgment.