A voltage divider uses two resistors to turn a higher voltage into a lower one. The output is Vout = Vin × R2 ÷ (R1 + R2), so 12 V through a 10 kΩ and a 4.7 kΩ resistor gives about 3.84 V. This free voltage divider calculator finds Vout, R1, R2 or Vin, suggests standard resistor values, and shows what your multimeter will actually read.
Voltage divider calculator
Find the output voltage, a resistor value or the input voltage of a two-resistor divider. Type resistors like 10k, 4.7k, 4k7 or 1M.
Voltage Divider Formula
R1 is the resistor between the input and the output point. R2 is the resistor between the output point and ground. The same current flows through both, so the voltage splits between them in proportion to their resistance.
| To find | Formula |
|---|---|
| Output voltage | Vout = Vin × R2 ÷ (R1 + R2) |
| Bottom resistor | R2 = R1 × Vout ÷ (Vin − Vout) |
| Top resistor | R1 = R2 × (Vin − Vout) ÷ Vout |
| Input voltage | Vin = Vout × (R1 + R2) ÷ R2 |
| Current | I = Vin ÷ (R1 + R2) |
Worked Example: 12 V to 5 V
- Pick R2 = 10 kΩ.
- R1 = 10 kΩ × (12 − 5) ÷ 5 = 14 kΩ.
- 14 kΩ is not a standard value, so use 15 kΩ. The output is 12 × 10 ÷ 25 = 4.8 V.
- The current is 12 V ÷ 25 kΩ = 0.48 mA, so any small resistor (1/8 W or more) is fine.
If you also need watts or current for a single resistor, the Ohm’s law calculator does that.
Common Voltage Divider Values
These pairs use standard E24 resistor values and never give more than the target voltage, which matters when the output goes into a 3.3 V or 5 V input pin.
| Divide | Typical use | R1 | R2 | Actual Vout |
|---|---|---|---|---|
| 5 V → 3.3 V | 5 V logic to a 3.3 V board | 3.9 kΩ | 7.5 kΩ | 3.29 V |
| 5 V → 2.5 V | Half of 5 V | 4.7 kΩ | 4.7 kΩ | 2.50 V |
| 9 V → 5 V | 9 V battery to 5 V input | 12 kΩ | 15 kΩ | 5.00 V |
| 12 V → 5 V | 12 V to a 5 V input | 47 kΩ | 33 kΩ | 4.95 V |
| 12 V → 3.3 V | 12 V to a 3.3 V input | 18 kΩ | 6.8 kΩ | 3.29 V |
| 14.4 V → 3.3 V | Car battery (up to 14.4 V) to 3.3 V | 16 kΩ | 4.7 kΩ | 3.27 V |
| 24 V → 5 V | 24 V to a 5 V input | 18 kΩ | 4.7 kΩ | 4.97 V |
| 24 V → 3.3 V | 24 V to a 3.3 V input | 39 kΩ | 6.2 kΩ | 3.29 V |
| 48 V → 5 V | 48 V to a 5 V input | 130 kΩ | 15 kΩ | 4.97 V |
Why the Output Drops When You Connect Something
Anything you connect to the output sits in parallel with R2, which lowers the bottom resistance and pulls Vout down. This is called loading. A simple rule: keep the load resistance at least 10 times R2 for an error under about 5%, and 100 times R2 for under 0.5%.
Your multimeter is a load too. A digital multimeter has an input resistance of about 10 MΩ. Two 1 MΩ resistors across 10 V should give 5 V, but the meter reads about 4.76 V. Two 10 kΩ resistors read 5.00 V, because 10 MΩ is far bigger than 10 kΩ. The calculator above shows the expected meter reading for your values. My voltmeter vs multimeter guide explains input impedance in more detail.
How to Check a Voltage Divider with a Multimeter
- With the power off, measure R1 and R2 on the resistance setting. If a reading looks wrong in circuit, lift one leg, because other parts can change it. You can confirm the marked value with the resistor color code calculator.
- Turn the power on and set the meter to DC volts. Put the black probe on ground.
- Touch the red probe to the top of R1 to read Vin.
- Touch the red probe to the point between R1 and R2 to read Vout.
- Compare the readings with the calculator.
| What you measure | Likely cause |
|---|---|
| Vout is 0 V | R2 is shorted, R1 is open, or there is no input voltage |
| Vout equals Vin | R2 is open (broken) or R1 is shorted |
| Vout is a little low | The load on the output, or very large resistor values with your meter |
| Vout is far from the calculated value | Wrong resistor value fitted, or a resistor has drifted |
New to resistance checks? See how to measure resistance with a multimeter.
Choosing Resistor Values
- Not too small: low values waste current and heat up. 12 V across 200 Ω is 60 mA and 0.72 W, which needs bigger resistors.
- Not too large: high values are easily pulled down by the load and by your meter. Above about 1 MΩ, readings get unreliable.
- Good middle ground: a total of 10 kΩ to 100 kΩ suits most sensing jobs, such as reading a battery with an Arduino or ESP32.
- Power rating: each resistor dissipates P = I² × R. Choose a rating at least twice that. The calculator suggests one for you.
Where Voltage Dividers Are Used
- Measuring a battery voltage with a microcontroller, which can only read up to 3.3 V or 5 V
- Dropping a 5 V logic signal to 3.3 V for slower signals
- Potentiometers, which are adjustable voltage dividers
- Sensors such as thermistors and light-dependent resistors, paired with a fixed resistor
- The feedback pin of adjustable voltage regulators
A divider is not a power supply. To run a device at a lower voltage, use a regulator or a buck converter.
Frequently Asked Questions
What is the voltage divider formula?
Vout = Vin × R2 ÷ (R1 + R2), where R1 is the resistor from the input to the output and R2 is the resistor from the output to ground. With two equal resistors, the output is exactly half the input.
How do I get 5 V from 12 V with resistors?
Use R1 = 15 kΩ and R2 = 10 kΩ, which gives about 4.8 V. That works for sensing or a signal input, but not for powering anything. To power a 5 V device from 12 V, use a voltage regulator or a buck converter.
How do I convert 5 V to 3.3 V with resistors?
R1 = 1 kΩ and R2 = 2 kΩ gives 3.33 V, and R1 = 1 kΩ with R2 = 1.8 kΩ gives 3.21 V if you must stay under 3.3 V. This is fine for slow logic signals going into a 3.3 V board. Fast signals and power need a level shifter or a regulator.
Why does my multimeter read lower than the calculated voltage?
A multimeter has an input resistance of about 10 MΩ, and it sits in parallel with R2. With large resistors, such as 1 MΩ, the meter pulls the reading down by a few percent. With resistors of 100 kΩ or less, the effect is too small to notice.
Can I use a voltage divider to power a device?
No. As soon as a device draws current, the output voltage drops and keeps changing with the load. Dividers are for signals and voltage sensing. Use a regulator to power things.
What resistor values should I use?
For most sensing jobs, a total of 10 kΩ to 100 kΩ works well. Lower values waste more current, and higher values are more affected by whatever you connect to the output, including your multimeter.
Does a voltage divider work with AC?
Yes. Resistors divide AC in the same ratio as DC. Never build your own divider to measure mains voltage, though. Use a multimeter rated for it.