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Voltage Divider Calculator

Instantly compute the output voltage (Vout), current and dissipated power of a two-resistor voltage divider.

Output Vout
6 V
Vout = Vin·R2/(R1+R2)
Current
0.6 mA
through the divider
Total power
7.2 mW
dissipated in R1+R2

Tip: keep the divider current well above any load on Vout, or add a buffer — loading R2 pulls the output down.

Disclaimer: This calculator is provided for general informational and educational purposes only, on an “as is” basis and without any warranty of accuracy or fitness for a particular purpose. Results may contain errors — always verify independently before relying on them in real designs. PartAndStock accepts no liability for any loss or damage arising from use of this tool, including when embedded on third-party sites.

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Learn the theory: What Is a Voltage Divider?

How to use

  1. 1Enter the input voltage (Vin).
  2. 2Enter the top resistor as R1 and the bottom resistor (where the output is taken) as R2.
  3. 3Output voltage, current and power are calculated instantly.

How it works

Enter the input voltage and two resistor values to get the divider's output voltage, the current through it and the total power.

Vout = Vin · R2 / (R1 + R2) · I = Vin / (R1 + R2) · P = Vin · I

How a voltage divider works

A voltage divider taps a lower voltage from the midpoint of two series resistors. Because the same current flows through both, the voltage splits in proportion to the resistances: the output is the drop across R2, so Vout = Vin·R2/(R1+R2). Larger R2 pushes the output toward Vin; larger R1 pulls it down.

Loading effect and correct use

The formula gives the unloaded (open-circuit) output. Connect a load and it appears in parallel with R2, dragging the output down. Rule of thumb: make the divider current at least 10× the load current, or isolate the output with an op-amp buffer. A divider draws current continuously, so choose large values in battery circuits.

Worked examples

  • Vin=12 V, R1=10 kΩ, R2=10 kΩ → Vout = 12·10/(10+10) = 6 V
  • Vin=5 V, R1=2.2 kΩ, R2=3.3 kΩ → Vout = 5·3.3/5.5 = 3.0 V
  • Vin=9 V, R1=1 kΩ, R2=1 kΩ → I = 9/2000 = 4.5 mA, P = 40.5 mW

Common Divider Ratios

R1R2Ratio (Vout/Vin)
10 kΩ10 kΩ0.50
10 kΩ20 kΩ0.67
20 kΩ10 kΩ0.33
1 kΩ3 kΩ0.75
3 kΩ1 kΩ0.25

Frequently Asked Questions

What is the voltage divider formula?+
Vout = Vin · R2 / (R1 + R2), where R2 is the bottom resistor across which the output is taken. E.g. 12 V with R1=R2=10 kΩ → 6 V.
Can I draw load current from a voltage divider?+
Only a little. The load sits in parallel with R2 and lowers the output. Make the divider current ~10× the load current, or buffer the output with an op-amp.
Which resistor values should I choose?+
The ratio R1/R2 sets the output, not the absolute value. Low values are more stable but waste current/heat; high values save current but are noise- and loading-sensitive. The kΩ range suits most jobs.
Can I use a divider as a voltage regulator?+
No. A divider can't hold the output steady as the load changes. Use a regulator or reference (e.g. LM317) for a fixed rail; a divider is only for signal/measurement level-shifting.
How much power does a divider dissipate?+
P = Vin·I = Vin²/(R1+R2). E.g. 12 V across a total of 20 kΩ dissipates just 7.2 mW. It rises fast at low resistances, so prefer large values in battery circuits.

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