Voltage Divider Calculator
Easily calculate output voltage and resistor values for your voltage divider circuits with our free online calculator. Perfect for hobbyists and engineers.
Circuit Diagram
Output Voltage (Vout)
5.000 V
Current
5.000 mA
Total Resistance
2.000 kΩ
Total Power
50.000 mW
What is a Voltage Divider?
A voltage divider is a simple but fundamental electronic circuit that turns a large voltage into a smaller one. Using just two resistors in series, it provides an output voltage that is a fraction of the input voltage. This circuit is one of the most common and useful building blocks in electronics for creating reference voltages, interfacing with sensors, and much more.
The Formula
The output voltage (Vout) of an unloaded divider is determined by this formula:
Vout = Vin * ( R2 / (R1 + R2) )
How It Works
The principle is based on Ohm's Law. The two resistors, R1 and R2, are connected in series across an input voltage source (Vin). Since they are in series, the same current flows through both.
- The total resistance of the circuit is
R1 + R2. - The current (I) flowing through the circuit is
I = Vin / (R1 + R2). - The voltage drop across R2 is
Vout = I * R2. - By substituting the expression for current, we get the main voltage divider formula.
The Loading Effect
When you connect a load (represented by the load resistor, RL) to the output of the voltage divider, it changes the circuit's behavior. The load resistor is in parallel with R2.
This combination creates a new equivalent resistance for the bottom part of the divider. The formula becomes:
Vout = Vin * ( R_eq / (R1 + R_eq) )
where R_eq = (R2 * RL) / (R2 + RL)
Generally, Vout will decrease under load. For the divider to be effective, the load resistance (RL) should be much larger (at least 10x) than R2.
Common Applications
- Reading Sensors: Many sensors, like photoresistors (LDRs) or thermistors, are variable resistors. A voltage divider converts their change in resistance into a change in voltage, which can be easily read by a microcontroller's ADC.
- Level Shifting: Safely connecting a high-voltage signal (e.g., 5V) to a lower-voltage input (e.g., 3.3V) by scaling the voltage down to an acceptable level.
- Creating Reference Voltages: Generating a stable, known voltage for components like op-amps or analog-to-digital converters (ADCs) to use as a reference point.