Voltage Divider Calculator
Calculate output voltage from two resistors, or find the resistor pair that hits a target voltage. Nearest E-series match included.
- Vout
- 2.5000 V
- Ratio
- 0.5000
- Static current
- 0.250 mA
Vout = Vin · R2 / (R1 + R2). Static current = Vin / (R1 + R2).
Higher total resistance = less quiescent current draw but more sensitivity to load current (any current sourced/sunk at the divider midpoint shifts Vout). Standard rule: divider current should be at least 10× the current drawn by whatever is measuring Vout (e.g. an ADC input).
How to size a voltage divider for an ADC
For a battery voltage sense feeding a microcontroller ADC (typically 100 kΩ input impedance), keep the total divider resistance below 10 kΩ so the ADC doesn't perturb the reading. For pure level-shifting into a high-impedance op-amp, higher values (100 kΩ+) save power.
Why the divider ratio can drift
Real resistors have tolerance (±1%, ±5%). Two 1% resistors can combine to give a divider ratio off by up to ~2%. For precision, use 0.1% resistors or trim with a series adjustment.
Frequently asked
- How to calculate voltage divider?
- Vout = Vin × R2 / (R1 + R2). If you know Vin and want a specific Vout, pick R1 and solve for R2: R2 = R1 × Vout / (Vin − Vout).
- What is a voltage divider used for?
- Level-shifting a signal into a lower-voltage ADC or logic input, sensing battery voltage, setting reference voltages, biasing transistors. Not suitable for delivering current — use a regulator.
- How much current does a voltage divider draw?
- I = Vin / (R1 + R2). A 5 V divider with two 10 kΩ resistors draws 0.25 mA continuously.
- Can I use a voltage divider to power a device?
- Not reliably. The output voltage drops as soon as the load draws current. Use a regulator (LDO, buck) for power; use a divider only for sensing/reference.
Dividers usually feed an ADC pin. Describe the sensor and the microcontroller, and PCBEditor wires the divider in and routes the board.
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