Voltage divider values for common conversions
These come from the "R2 for a target Vout" mode of the Voltage Divider calculator: R2 = Vout · R1 / (Vin − Vout), then the largest E24 value that keeps the output at or below the target, so an ADC input or pin limit is never exceeded. The nearest E24 value is shown too when it differs; it lands slightly above the target. Each "open" link loads the calculator with those inputs.
Two common choices for R1 are shown. 10 kΩ gives a low output impedance that suits most ADCs without extra parts, but draws more current. 100 kΩ draws ten times less current, which suits battery-powered devices, but usually needs a capacitor (for example 100 nF) from the ADC pin to ground.
Values
| Vin | Target Vout | R1 | Exact R2 | E24 R2 (Vout ≤ target) | Vout with that R2 | Error | Nearest E24 R2 (Vout) | Divider current | Output impedance R1∥R2 | Prefilled link |
|---|---|---|---|---|---|---|---|---|---|---|
| 5 V | 3.3 V | 10 kΩ | 19.41 kΩ | 18 kΩ | 3.214 V | -2.6 % | 20 kΩ (3.333 V, above target) | 178.6 µA | 6.429 kΩ | open |
| 4.2 V | 3.3 V | 10 kΩ | 36.67 kΩ | 36 kΩ | 3.287 V | -0.395 % | same | 91.3 µA | 7.826 kΩ | open |
| 9 V | 3.3 V | 10 kΩ | 5.789 kΩ | 5.6 kΩ | 3.231 V | -2.1 % | same | 576.9 µA | 3.59 kΩ | open |
| 12 V | 3.3 V | 10 kΩ | 3.793 kΩ | 3.6 kΩ | 3.176 V | -3.74 % | 3.9 kΩ (3.367 V, above target) | 882.4 µA | 2.647 kΩ | open |
| 12 V | 5 V | 10 kΩ | 7.143 kΩ | 6.8 kΩ | 4.857 V | -2.86 % | 7.5 kΩ (5.143 V, above target) | 714.3 µA | 4.048 kΩ | open |
| 15 V | 3 V | 10 kΩ | 2.5 kΩ | 2.4 kΩ | 2.903 V | -3.23 % | same | 1.21 mA | 1.935 kΩ | open |
| 24 V | 3.3 V | 10 kΩ | 1.594 kΩ | 1.5 kΩ | 3.13 V | -5.14 % | 1.6 kΩ (3.31 V, above target) | 2.087 mA | 1.304 kΩ | open |
| 24 V | 5 V | 10 kΩ | 2.632 kΩ | 2.4 kΩ | 4.645 V | -7.1 % | 2.7 kΩ (5.102 V, above target) | 1.935 mA | 1.935 kΩ | open |
| 5 V | 3.3 V | 100 kΩ | 194.1 kΩ | 180 kΩ | 3.214 V | -2.6 % | 200 kΩ (3.333 V, above target) | 17.86 µA | 64.29 kΩ | open |
| 4.2 V | 3.3 V | 100 kΩ | 366.7 kΩ | 360 kΩ | 3.287 V | -0.395 % | same | 9.13 µA | 78.26 kΩ | open |
| 9 V | 3.3 V | 100 kΩ | 57.89 kΩ | 56 kΩ | 3.231 V | -2.1 % | same | 57.69 µA | 35.9 kΩ | open |
| 12 V | 3.3 V | 100 kΩ | 37.93 kΩ | 36 kΩ | 3.176 V | -3.74 % | 39 kΩ (3.367 V, above target) | 88.24 µA | 26.47 kΩ | open |
| 12 V | 5 V | 100 kΩ | 71.43 kΩ | 68 kΩ | 4.857 V | -2.86 % | 75 kΩ (5.143 V, above target) | 71.43 µA | 40.48 kΩ | open |
| 15 V | 3 V | 100 kΩ | 25 kΩ | 24 kΩ | 2.903 V | -3.23 % | same | 121 µA | 19.35 kΩ | open |
| 24 V | 3.3 V | 100 kΩ | 15.94 kΩ | 15 kΩ | 3.13 V | -5.14 % | 16 kΩ (3.31 V, above target) | 208.7 µA | 13.04 kΩ | open |
| 24 V | 5 V | 100 kΩ | 26.32 kΩ | 24 kΩ | 4.645 V | -7.1 % | 27 kΩ (5.102 V, above target) | 193.5 µA | 19.35 kΩ | open |
Notes
- Error is the difference between the output with the chosen E24 resistor and the target. It is never positive, because R2 is rounded down. The "Nearest E24 R2" column shows the closer value when it differs, for example 5 V to 3.3 V: 20 kΩ gives 3.333 V, above a 3.3 V limit, so the table picks 18 kΩ (3.214 V). If you need to get closer, use a 1% (E96) value and check again.
- 4.2 V to 3.3 V is for a single Li-ion or LiPo cell at full charge. It reads 3.287 V at 4.2 V.
- 15 V to 3 V is a 12 V lead-acid battery monitor with headroom for 14.4 V charging. See the worked example.
- Divider current flows all the time, including when the device sleeps. 2.087 mA (24 V, 10 kΩ) is about 1.5 Ah per month.
- Output impedance is R1 ∥ R2. Many ADC datasheets recommend 10 kΩ or less; above that, add a capacitor or a buffer.
- Resistor tolerance is not included. Use 1% resistors for measurement.
Share-link format
https://ohmlark.com/calculators/voltage-divider?mode=r2&vin=<Vin V>&r1=<R1>&vout=<target V>
https://ohmlark.com/calculators/voltage-divider?mode=vout&vin=<Vin V>&r1=<R1>&r2=<R2>&rl=<load, optional>
Resistances accept SI shorthand such as 10k, 4k7 or 1M. mode must be vout or r2.