Voltage Divider
Calculate output voltage for resistor divider circuits. Enter circuit values to calculate the selected electrical quantity.
Input & Resistors
Electronics guide · Electrical power, energy, and wiring
About Voltage Divider Calculator
A voltage divider uses two resistors in series to produce an output voltage from an input. This calculator estimates the unloaded output and current using the resistor values entered. A connected load can change the result, so treat the simple divider as an initial calculation.
Power and energy calculations relate quantities such as voltage, current, resistance, time, and load. AC and DC systems can require different assumptions, and a calculated estimate is not a substitute for checking source capability, wire ratings, protection, efficiency, and equipment specifications.
How to Use This Tool
- 1.Enter the input voltage and the values for the upper resistor R1 and lower resistor R2.
- 2.Check that resistance units match and that values are positive.
- 3.Calculate and review output voltage, total resistance, and circuit current. If a load is connected, include its effect before relying on the output.
Technical Details to Check
1.Check AC or DC assumptions
In AC calculations, voltage and current may refer to RMS values, and phase relationships can affect real power. Do not apply a DC relationship to an AC system unless the tool's stated assumptions fit.
2.Power is not the same as energy
Watts describe a rate of energy use; watt-hours and joules describe an amount of energy over time. A runtime or consumption estimate needs both a load and a duration or duty profile.
3.Real systems lose energy
Inverters, batteries, wiring, motors, and power supplies are not perfectly efficient. Confirm whether the selected calculation includes efficiency, power factor, voltage drop, or only ideal values.
4.Ratings and protection are essential
An estimated current or power value does not determine a safe wire size, fuse, battery connection, or supply. Follow applicable standards, product ratings, and qualified design guidance.
How the Calculation Works
For the shown divider, Vout=Vin×R2/(R1+R2). The series current is Vin/(R1+R2) in the unloaded case. R2 is connected from the output node to ground in this standard arrangement.
Worked Example
With Vin=12 V and R1=R2=1 kΩ, Vout is 6 V and current through the pair is 6 mA before a load is attached.
Where This Tool Can Help
Estimate reference voltages, sensor input scaling, and simple resistive networks. A divider may be useful when the output load draws very little current compared with the resistor chain.
Estimating a load
Use known voltage and current or power figures to understand a device's approximate demand before checking its label and startup behavior.
Planning energy use
Combine a power estimate with realistic operating hours to compare possible consumption, while accounting separately for standby use and efficiency.
Checking a wiring estimate
Use current or voltage-drop results as an early check, then verify conductor size and protection with the correct installation rules and environment.
Comparing supply options
Compare candidate sources on the same voltage, current, power, and duration basis, and include headroom where the equipment specification requires it.
Tips for More Reliable Results
- Confirm whether voltage and current are RMS, peak, nominal, or measured under load.
- Keep watts, watt-hours, joules, and time units distinct when entering values.
- Include efficiency or power factor only when the tool provides that input and you have a suitable value.
- Check conductor, connector, battery, and supply ratings before using an estimate in a real installation.
Limitations and Assumptions
A load in parallel with R2 changes the effective lower resistance and lowers the output. Resistor tolerance, heating, source limits, and ADC input behavior may also matter. It is not a voltage regulator.
Electrical power tools estimate values from entered figures and stated assumptions. They do not measure a circuit, model every transient or loss, or certify wiring and equipment as safe. Confirm important designs with manufacturer data and applicable electrical requirements.
Frequently Asked Questions
Why is the output half the input with equal resistors?
Equal values split the input voltage evenly in the unloaded series pair.
Can I power a device from a divider?
Usually not if it draws meaningful current; the load changes the divider voltage.
Does a divider regulate voltage?
No. It provides a ratio under assumed conditions and does not actively correct for load or supply changes.
Are watts and watt-hours interchangeable?
No. Watts are a rate; watt-hours measure energy used over time.
Does a calculated value make a circuit safe to build?
No. Safety depends on ratings, protection, installation conditions, and applicable standards as well as the arithmetic.