Circuit design tool
Voltage divider calculator
Calculate unloaded or loaded voltage-divider output, current and resistor power. You can also work backward from a target voltage and compare practical E12 or E24 resistor pairs.
Calculated divider
Unloaded output
10 V
Divider current
1 mA
Total power
24 mW
Thevenin resistance
5.8333 kΩ
R1 power
14 mW
R2 power
10 mW
Loaded output
9.4488 V
Loading error
5.512%
Load affects output
The load pulls the divider output down by more than 5%. Use lower divider resistance or buffer the output.
- The load pulls the divider output down by more than 5%. Use lower divider resistance or buffer the output.
How to use the voltage divider calculator
Evaluate an existing two-resistor divider or design a practical pair for a target output.
- 01
Choose evaluate or design
Evaluate accepts your resistor values. Design searches the selected preferred-value series for pairs close to a target output.
- 02
Enter the circuit conditions
Set input voltage, upper resistor R1, lower resistor R2 and, when relevant, the load resistance connected across R2.
- 03
Review loading and power
Compare ideal and loaded output, check divider current and confirm each resistor's power against its rating and tolerance.
Voltage-divider equations
The model treats the source as ideal and the load as a resistance in parallel with R2.
Unloaded output
Vout = Vin × R2 / (R1 + R2)
Loaded lower leg
Rlower = R2 ∥ Rload
Loaded output
Vout = Vin × Rlower / (R1 + Rlower)
A connected load changes the effective lower-leg resistance and normally reduces the output. The design search ranks standard resistor pairs by voltage error; it does not choose component tolerance, temperature coefficient or a downstream buffer for you.
Do not use a passive divider as a regulated power supply. Confirm input range, resistor voltage and power ratings, source impedance, load variation, tolerance and fault behavior before releasing hardware.
Practical checks before building
A mathematically correct ratio can still be unsuitable in a real circuit.
Account for the real load
ADC inputs, bias networks and test instruments can all load a divider. Use the minimum expected load resistance for a conservative check.
Check source impedance
High resistor values reduce current but increase output impedance, settling time and sensitivity to leakage, noise and input bias current.
Check tolerance and drift
Calculate worst-case output using resistor tolerance and temperature coefficient when the voltage threshold matters.
Check component stress
Verify resistor power and working-voltage ratings at the maximum possible input voltage, including transients.
Frequently asked questions
Why is the loaded output lower than the ideal output?
The load sits in parallel with R2, reducing the effective lower-leg resistance. That changes the divider ratio and pulls the output down.
Can a voltage divider power a sensor or module?
Usually not reliably. Load current changes the output voltage, so an active regulator or buffered reference is normally more appropriate for powering a device.
Should I choose large or small resistor values?
Smaller values improve stiffness but waste more current and dissipate more power. Larger values save current but are more sensitive to loading, leakage, noise and settling time.
What do E12 and E24 mean?
They are preferred resistor-value series. E24 provides more values per decade than E12, so it often permits a closer ratio using standard parts.
Related engineering resources
Time constant calculator
Check the RC response created by a divider and a connected capacitance.
Open resource
Low-pass and high-pass filter calculator
Evaluate first-order RC, RL and ideal LC cutoff behavior.
Open resourceAll engineering tools
Browse the current set of tested electrical and RF calculators.
Open resource