Voltage Divider Calculator
This voltage divider calculator gives the output voltage from the input voltage and the resistors R1 and R2, with an optional load resistor, or finds the R2 you need for a target voltage.
Example: What to calculate: Output voltage · Input voltage 12 V · R1 (top, to the input voltage) 10,000 Ω · R2 (bottom, to ground) 4,700 Ω · Load resistance 0 Ω → Result: 3.837 V output voltage. Source: Wikipedia – Spannungsteiler (Formel, belasteter Teiler). Updated: .
How it is calculated
A divider of R1 = 10 kΩ and R2 = 4.7 kΩ on 12 V gives 3.84 V. The output is the fraction R2 / (R1 + R2) of the input voltage, as long as nothing draws current from the output.
How it is calculated
Both resistors are in series and carry the same current, so the voltage splits in proportion to the resistances: Vout = Vin · R2 / (R1 + R2). A load on the output sits in parallel with R2 and lowers the lower leg, so the calculator uses R2 ∥ RLoad. The second mode solves the formula for R2 and also names the nearest value from the E12 series (IEC 60063) together with the voltage you get with it.
Practical tips
- Keep the divider current at least ten times the load current, otherwise the voltage drifts noticeably.
- Check the power rating of the resistors, especially at high voltages and small values.
- For microcontroller inputs (for example 12 V down to 3.3 V) use resistors with 1 % tolerance.
Frequently asked questions
How do you calculate a voltage divider?
Use Vout = Vin · R2 / (R1 + R2). R1 connects to the input voltage, R2 to ground, and the output is taken between them.
How do you calculate a loaded voltage divider?
The load is in parallel with R2. Use R2 · RLoad / (R2 + RLoad) in place of R2. The calculator does this as soon as you enter a load resistance.
How do I find R2 for a target voltage?
Rearranged, R2 = R1 · Vout / (Vin − Vout). Choose the mode “R2 for a target voltage”; the nearest E12 value is shown as well.
Can a voltage divider power a device?
Only very light loads. When the current changes, the voltage changes too. Use a regulator or converter to supply a device.
Sources and legal basis
- Wikipedia – Spannungsteiler (Formel, belasteter Teiler)
- Wikipedia – Voltage divider (Uout = Uin · R2/(R1+R2), Last parallel zu R2)
- Wikipedia – E series of preferred numbers (IEC 60063, E12)
As of: · Editorial policy
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