Quick answer
A resistive divider gives V_out = V_in × R₂ ÷ (R₁ + R₂). With 12 V across R₁ = 10 kΩ (top) and R₂ = 5 kΩ (bottom), V_out = 4 V and the current is 0.8 mA.
Enter the input voltage and the two resistances. The calculator returns the output voltage and the current.
Related tools: RMS Voltage Calculator: Convert between RMS, peak and peak-to-peak voltage of a sine wave. Current Divider Calculator: Current through each of two parallel resistors. RLC Impedance Calculator: Impedance and phase angle of a series RLC circuit.
How to use the Voltage Divider Calculator
- Enter input voltage (V) (above 0).
- Enter r1 (top) (Ω) (above 0).
- Enter r2 (bottom) (Ω) (above 0).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Input voltage | A number, in V | > 0 |
| R1 (top) | A number, in Ω | > 0 |
| R2 (bottom) | A number, in Ω | > 0 |
Formula and method
Formula
V_out = V_in × R2 ÷ (R1 + R2)
IEEE-754 double precision; shown to the decimals indicated.
Unloaded divider.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Input voltage = 12; R1 (top) = 10000; R2 (bottom) = 5000.
| Result | Value |
|---|---|
| Output voltage | 4 V |
| Current | 0.0008 A |
Example 2
Inputs: Input voltage = 5; R1 (top) = 4700; R2 (bottom) = 10000.
| Result | Value |
|---|---|
| Output voltage | 3.401361 V |
| Current | 0.00034 A |
Example 3
Inputs: Input voltage = 9; R1 (top) = 1000; R2 (bottom) = 1000.
| Result | Value |
|---|---|
| Output voltage | 4.5 V |
| Current | 0.0045 A |
The first line is the headline result (output voltage). Below it the voltage Divider Calculator lists current, which describe the same case from other angles. IEEE-754 double precision; shown to the decimals indicated.
Loading effect
The formula assumes nothing draws current from the output. A load in parallel with R₂ lowers the output: with a 5 kΩ load the bottom resistance falls to 2.5 kΩ and V_out drops to 2.4 V. Keep the load much larger than R₂ or use a buffer.
Applications
Dividers scale sensor voltages to an ADC range, set bias points and level-shift logic signals. Higher resistances waste less current but are more sensitive to loading and noise.
How the result changes with input voltage
Holding every other input at the first worked example, this table changes only input voltage. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Input voltage | Output voltage | Current |
|---|---|---|
| 6 | 2 V | 0.0004 A |
| 12 | 4 V | 0.0008 A |
| 24 | 8 V | 0.0016 A |
| 48 | 16 V | 0.0032 A |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Input voltage: entering "0" shows "Input voltage must be greater than 0." beside that field and no result.
- R2 (bottom): entering "0" shows "R2 (bottom) must be greater than 0." beside that field and no result.
Choosing between the Voltage Divider Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [RMS Voltage Calculator](/engineering/rms-voltage-calculator/) | i know the and voltage | RMS voltage |
| [Current Divider Calculator](/engineering/current-divider-calculator/) | total current, r1 and r2 | Current through R1 |
| [RLC Impedance Calculator](/engineering/rlc-impedance-calculator/) | resistance, inductance and capacitance | Impedance |
| [Parallel Plate Capacitor Calculator](/engineering/parallel-plate-capacitance-calculator/) | plate area, plate separation and relative permittivity εr | Capacitance |
| [Inductive Reactance Calculator](/engineering/inductor-reactance-calculator/) | inductance and frequency | Inductive reactance |
Background: electrical circuits
Ohm's law links voltage, current and resistance: V = I × R, so I = V ÷ R and R = V ÷ I. Power is P = V × I, which also equals I² × R and V² ÷ R.
These relations hold for ohmic components, where resistance is constant. Diodes and transistors are non-linear, and in AC circuits with reactive parts impedance (Z) takes the place of resistance. Check component ratings and local electrical code before relying on any calculation.
Assumptions and limitations
- A load in parallel with R2 lowers the output
Use results as engineering estimates and check them against the governing standards, safety factors and a qualified engineer's judgement before relying on them.
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for input voltage and r2 (bottom) to confirm this.
Frequently asked questions
How do I get 3.3 V from 5 V?
Use R₁ = 1.7 kΩ and R₂ = 3.3 kΩ in proportion.
Does a divider supply power?
Not efficiently. A divider delivers little current without the output sagging, so use it for signals, not power.
What is the current through both?
The current is V_in ÷ (R₁ + R₂); in the example 12 V ÷ 15 kΩ = 0.8 mA through both resistors.
What does the Voltage Divider Calculator calculate?
Output voltage of a two-resistor divider. It returns Output voltage and Current.
What formula does the Voltage Divider Calculator use?
V_out = V_in × R2 ÷ (R1 + R2). Unloaded divider.
What do I need to enter in the voltage Divider Calculator?
You enter Input voltage (V), R1 (top) (Ω) and R2 (bottom) (Ω).
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. A load in parallel with R2 lowers the output.
What is an example of a voltage Divider result?
With input voltage 12, r1 (top) 10000 and r2 (bottom) 5000, the output voltage is 4 V.
Can I rely on this calculator for a decision?
Use results as engineering estimates and check them against the governing standards, safety factors and a qualified engineer's judgement before relying on them. For this calculator in particular: A load in parallel with R2 lowers the output.
Related calculators
- RMS Voltage Calculator — Convert between RMS, peak and peak-to-peak voltage of a sine wave.
- Current Divider Calculator — Current through each of two parallel resistors.
- RLC Impedance Calculator — Impedance and phase angle of a series RLC circuit.
- Parallel Plate Capacitor Calculator — Capacitance of two parallel plates.
- Inductive Reactance Calculator — Reactance of an inductor at a frequency.
- RC Circuit Calculator — Time constant, cutoff frequency and charge level of an RC circuit.
Sources
- OpenStax, University Physics Volume 2 (Rice University): electricity, circuits and thermodynamics
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.