Calculate output voltage and resistor values for voltage divider circuits.
How to Use This Calculator
1
Enter Input Voltage
Input the source voltage (Vin) supplied to the divider circuit.
2
Set Resistor Values
Enter the values for R1 (top resistor) and R2 (bottom resistor) in ohms, kilohms, or megohms.
3
Read Output Voltage
The calculator shows the output voltage (Vout) across R2, plus current flow and power dissipation in each resistor.
Key Terms
- Voltage Divider
- A simple circuit of two series resistors that produces an output voltage that is a fraction of the input voltage.
- Quiescent Current
- The current flowing through the divider when no load is connected. Lower quiescent current means less wasted energy.
- Load Effect
- When a load is connected across R2, it forms a parallel combination that reduces the effective R2 value and lowers Vout.
- Impedance Matching
- The practice of matching source and load impedances for maximum power transfer, important in audio and RF circuits.
- Bleeder Resistor
- A resistor that discharges stored energy in a power supply when it is turned off, improving safety.
Real-World Examples
Example 1
5V to 3.3V Level Shift
Vin: 5V, R1: 1.7K ohms, R2: 3.3K ohms
Result: Vout = 5 × 3300 / (1700 + 3300) = 3.3V. This is commonly used to interface 5V Arduino outputs with 3.3V sensors.
Example 2
Battery Voltage Monitor
Vin: 12V, R1: 10K ohms, R2: 3.3K ohms
Result: Vout = 12 × 3300 / (10000 + 3300) = 2.98V. This scales a 12V battery voltage down to a safe range for a microcontroller ADC input.
Voltage Divider Ratio Examples
| R1 | R2 | Ratio (R2/(R1+R2)) | 12V Input → Vout |
|---|
| 10K | 10K | 0.500 | 6.00V |
| 10K | 4.7K | 0.320 | 3.84V |
| 10K | 3.3K | 0.248 | 2.98V |
| 10K | 1K | 0.091 | 1.09V |
Voltage Dividers in Modern Electronics
When to Use a Voltage Divider
Voltage dividers are ideal for signal-level voltage scaling, sensor biasing, and ADC reference inputs where the load current is very small. They are simple, cheap, and require no active components. However, they are not suitable for powering loads that draw significant current because the output voltage will sag.
Avoiding Common Mistakes
The most common error is ignoring load resistance. If R2 is 10K and the load is also 10K, the effective lower resistance drops to 5K, cutting the output voltage significantly. For stable outputs under load, use a voltage regulator instead. Also, very high resistor values can introduce noise in sensitive analog circuits.