Voltage Divider Calculator
This voltage divider calculator finds the output voltage, divider current, power dissipation, and output impedance of a two-resistor divider. Enter the supply voltage, R1, and R2 to get all key circuit parameters instantly.
Circuit parameters
Vin ─┬─ R1 ─┬─ R2 ─ GND
└─ Vout
└─ Vout
Voltage divider formula
Vout = Vin × R2 ÷ (R1 + R2)
I = Vin ÷ (R1 + R2)
Zout = R1 ∥ R2 = (R1 × R2) ÷ (R1 + R2)
A common use case: interface a 5 V sensor to a 3.3 V ADC. You need Vout/Vin = 3.3/5 = 0.66, so R2/(R1+R2) = 0.66, meaning R2/R1 ≈ 1.94. Standard values: R1 = 10 kΩ, R2 = 20 kΩ gives Vout = 5 × 20/(10+20) = 3.33 V.
Common Questions
Frequently asked questions
- What is a voltage divider?
- A voltage divider is a simple circuit with two resistors in series connected across a supply voltage (Vin). The output voltage (Vout) is taken from the junction between the two resistors. Because the resistors share the total voltage in proportion to their values, you can choose R1 and R2 to produce any fraction of Vin at the output — for example, to create a reference voltage, bias a transistor, or interface two logic levels.
- What is the voltage divider formula?
- Vout = Vin × R2 ÷ (R1 + R2). R1 is the top resistor (between Vin and the output node) and R2 is the bottom resistor (between the output node and ground). The same current flows through both resistors because they are in series: I = Vin ÷ (R1 + R2).
- How do I choose R1 and R2 for a target output voltage?
- Rearranging the formula: R2 ÷ R1 = Vout ÷ (Vin − Vout). Choose a ratio first, then select standard resistor values that are close to that ratio while keeping the total resistance (R1 + R2) high enough that the divider does not load your source and low enough that the output impedance is acceptable for whatever you connect to it.
- What is loading effect in a voltage divider?
- If a load resistance RL is connected to Vout, it appears in parallel with R2, changing the effective bottom resistance and thus the output voltage. To minimise loading effect, the load resistance should be at least 10× larger than R2. When no load is connected, the divider is unloaded and the formula holds exactly.
- What is the output impedance of a voltage divider?
- The Thevenin output impedance of a voltage divider is R1 parallel R2 = (R1 × R2) ÷ (R1 + R2). This is the source resistance seen by any load connected to Vout. A lower output impedance means the divider is less sensitive to loading, but uses more current and dissipates more power.
- What are practical uses of voltage dividers?
- Voltage dividers are used to: set the reference voltage for an op-amp or comparator, create a midpoint supply for audio circuits, bias the base of a BJT transistor, interface a 5V sensor to a 3.3V ADC input, build a potentiometer (volume control), and divide down a high voltage for safe measurement with a lower-voltage ADC.
- Can a voltage divider supply power to a load?
- A resistive voltage divider is unsuitable as a power supply because its output voltage droops significantly under load, and it wastes power as heat even with no load. For powering a circuit, use a voltage regulator instead. Voltage dividers are best used for signal-level applications where the current drawn by the load is negligible.