Voltage Divider Calculator
Enter the input voltage and two resistor values to find the output voltage of your voltage divider circuit. Or enter Vout to find the required resistor ratio.
Reviewed by the ToolNestr Editorial Team — July 2026
What different voltage division ratios mean
The output voltage as a percentage of input voltage determines how much the signal is attenuated. Different ratios suit different applications.
Circuit Designer
Design bias networks, level shifters and reference voltage sources for analog and digital circuits quickly.
Sensor User
Scale sensor outputs to match ADC input ranges, ensuring maximum resolution in your data acquisition system.
Student
Learn the fundamental concept of voltage division by experimenting with different resistor values and observing the results.
Audio Engineer
Design passive attenuator pads, volume controls and signal level matching networks for audio equipment.
| Ratio (Vout/Vin) | R1 : R2 | Example R1 | Example R2 | Typical use |
|---|---|---|---|---|
| 0.10 | 9 : 1 | 9 k\u03a9 | 1 k\u03a9 | High-voltage ADC input |
| 0.25 | 3 : 1 | 7.5 k\u03a9 | 2.5 k\u03a9 | Battery level monitoring |
| 0.33 | 2 : 1 | 6.8 k\u03a9 | 3.4 k\u03a9 | 3.3V from 5V logic |
| 0.50 | 1 : 1 | 10 k\u03a9 | 10 k\u03a9 | Mid-rail reference |
| 0.67 | 1 : 2 | 3.4 k\u03a9 | 6.8 k\u03a9 | 5V from 3.3V logic |
| 0.75 | 1 : 3 | 2.5 k\u03a9 | 7.5 k\u03a9 | LED dimming threshold |
| 0.90 | 1 : 9 | 1 k\u03a9 | 9 k\u03a9 | Near-rail reference |
How to use the Voltage Divider Calculator
Choose the mode
Select \u201cFind Vout\u201d to compute output voltage from resistor values, or \u201cFind R2\u201d to calculate the resistor needed for a target voltage.
Enter the values
Fill in Vin and the required resistor or target voltage values. All fields update instantly as you type.
Read the results
See the output voltage, voltage division ratio, and the current flowing through the divider. Use these to check loading effects.
Tips for designing voltage dividers
Keep divider current 10\u00d7 above load current
If your load draws 1 mA, design the divider to draw at least 10 mA. This ensures the load does not significantly alter the output voltage. Use the displayed divider current to verify.
Use standard resistor values
Choose resistors from the E12 or E24 series (10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82 and their multiples). This makes sourcing components practical.
Consider tolerance effects
A 5% resistor divider can have up to 10% error in Vout. For precision applications, use 1% or better resistors. The worst-case output voltage can be calculated from the resistor tolerances.
Use a buffer for variable loads
If the load current varies, the output voltage will vary too. Place an op-amp voltage follower between the divider and the load to eliminate loading effects entirely.
How voltage dividers work
A voltage divider is one of the most fundamental circuits in electronics. It consists of two resistors connected in series across a voltage source. The output voltage is tapped from the junction between the two resistors. Because the same current flows through both resistors (neglecting load current), the voltage drop across each resistor is proportional to its resistance.
The formula Vout = Vin \u00d7 R2 / (R1 + R2)
This simple formula is derived from Ohm\u2019s Law. The total resistance is R1 + R2, so the current is I = Vin / (R1 + R2). The voltage across R2 is Vout = I \u00d7 R2 = Vin \u00d7 R2 / (R1 + R2). The output is always less than the input, making this a passive attenuator.
Loading effects and impedance
The output impedance of a voltage divider is R1 || R2 (the parallel combination of both resistors). This impedance limits how much current can be drawn from the output. A rule of thumb: the load resistance should be at least 10\u00d7 the divider\u2019s output impedance to keep error under 10%.
Applications across electronics
Voltage dividers appear in nearly every electronic device. They scale battery voltages for ADC monitoring, set bias points for transistors and op-amps, shift logic levels between 5V and 3.3V systems, provide reference voltages for comparators, and form the basis of more complex circuits like Wheatstone bridges and attenuators.
Worked example
Frequently asked questions
What is a voltage divider?
A voltage divider is a passive circuit consisting of two resistors in series that produces an output voltage that is a fraction of the input voltage. The output voltage is determined by the ratio of the two resistors: Vout = Vin × R2 ÷ (R1 + R2).
What is the voltage divider formula?
The formula is Vout = Vin × R2 / (R1 + R2), where Vin is the input voltage, R1 is the resistor connected to the input, and R2 is the resistor connected to ground. The output is taken across R2.
How do I choose resistor values for a voltage divider?
Choose values that give the desired voltage ratio while keeping the current through the divider reasonable. A good rule is to make the current through the divider (I = Vin / (R1 + R2)) about 10–100 times larger than any load current drawn from Vout.
What is the loading effect in a voltage divider?
When a load is connected to the output of a voltage divider, it draws current that changes the effective resistance, altering Vout. To minimize loading, keep the divider resistors small relative to the load resistance, or use a buffer amplifier.
Can I use a voltage divider for voltage regulation?
No — voltage dividers are not regulated. Vout changes with the load current and input voltage variations. For stable voltage, use a voltage regulator IC instead of a resistor divider.
What is the difference between a voltage divider and a potential divider?
They are the same thing. Both terms refer to a resistor network that divides a voltage into a smaller proportion. The term potential divider is more common in British English.
How do I calculate R1 and R2 given Vout?
First determine the ratio R2 / (R1 + R2) = Vout / Vin. Choose a total current for the divider, calculate R1 + R2 = Vin / I, then solve for R2 = ratio × (R1 + R2) and R1 = (R1 + R2) – R2.
Can voltage dividers work with AC signals?
Yes, voltage dividers work with AC signals using the same formula for resistive dividers. For frequency-dependent dividers, capacitors or inductors replace one resistor to create high-pass or low-pass filters.
What is a loaded voltage divider?
A loaded voltage divider has a load resistor in parallel with R2, which changes the effective lower resistance. The new R2′ = (R2 × RL) ÷ (R2 + RL), and Vout is recalculated using this effective value.
What are common applications of voltage dividers?
Voltage dividers are used for ADC input scaling, sensor signal conditioning, setting bias voltages in transistor circuits, level shifting between logic families, and creating reference voltages.
Sources & references
This tool uses standard formulas and reference values from:
- • NFPA 70 — National Electrical Code (NEC), conduit fill, box fill and conductor ampacity. nfpa.org
- • IPC-2221, Generic Standard on Printed Board Design (trace width / current). ipc.org
- • NIST reference constants and unit definitions; IEEE standards where applicable. nist.gov
For educational and preliminary use. Verify against full engineering calculations and the governing standard before any real design.