How to use the voltage divider calculator
- Enter the input voltage, then R1 and R2 (10k, 4.7k and so on).
- Add a load resistance to see the loaded output.
- To choose resistors for a target, switch modes and pick the series and total resistance range.
Common voltage divider resistor pairs (E24)
Vout = Vin × R2 ÷ (R1 + R2). The table picks the closest E24 pair with a total between 10 kΩ and 100 kΩ. A load lowers the output; enter the load resistance in the calculator to check.
| Divider | R1 | R2 | Actual output | Error |
|---|---|---|---|---|
| 5 V → 3.3 V | 4.7 kΩ | 9.1 kΩ | 3.297 V | -0.09% |
| 5 V → 2.5 V | 5.1 kΩ | 5.1 kΩ | 2.5 V | 0% |
| 5 V → 1.8 V | 11 kΩ | 6.2 kΩ | 1.802 V | 0.13% |
| 3.3 V → 1.8 V | 10 kΩ | 12 kΩ | 1.8 V | 0% |
| 3.3 V → 1.2 V | 8.2 kΩ | 4.7 kΩ | 1.202 V | 0.19% |
| 12 V → 5 V | 18 kΩ | 13 kΩ | 5.032 V | 0.65% |
| 12 V → 3.3 V | 24 kΩ | 9.1 kΩ | 3.299 V | -0.03% |
| 24 V → 5 V | 9.1 kΩ | 2.4 kΩ | 5.009 V | 0.17% |
| 24 V → 3.3 V | 47 kΩ | 7.5 kΩ | 3.303 V | 0.08% |
| 24 V → 12 V | 5.1 kΩ | 5.1 kΩ | 12 V | 0% |
| 9 V → 5 V | 12 kΩ | 15 kΩ | 5 V | 0% |
| 48 V → 3.3 V | 27 kΩ | 2 kΩ | 3.31 V | 0.31% |
Frequently asked questions
What is the voltage divider formula?
Vout = Vin × R2 ÷ (R1 + R2), with R1 to the input and R2 to ground. 12 V with R1 = 10 kΩ and R2 = 4.7 kΩ gives about 3.84 V.
Can a divider power a load?
Not really. A load in parallel with R2 pulls the output down, more so at higher current. Dividers suit high-impedance inputs such as ADCs, comparators and feedback pins; use a regulator to power a load.
How large should the divider resistors be?
Too low wastes current and heats the resistors; too high makes the output sensitive to load, leakage and noise. 10–100 kΩ is common for ADC inputs; check the ADC source impedance requirement.
Are my inputs uploaded?
No. Everything is calculated locally in your browser and nothing is stored; a share link only carries the values you entered.
Results are for design estimates and part selection; for production and safety-related circuits follow component datasheets, applicable standards and measurements.