Calculates the output voltage across one resistor in a simple two-resistor series voltage divider circuit.
How it works
The input voltage is multiplied by the ratio of the second resistor to the sum of both resistors.
What this does not include
This assumes no current is drawn from the output (an “unloaded” divider) — connecting a load changes the effective resistance and shifts the actual output voltage lower.
How to use this calculator
- Enter the input voltage and both resistor values.
A worked example
A 12V input through resistors R1=1,000Ω and R2=2,000Ω: Vout = Vin × R2/(R1+R2) = 12 × 2000/3000 = 8V.
A 5V input through R1=470Ω and R2=1,000Ω: Vout = 3.4014V.
What the variables mean
| Variable | Meaning |
|---|---|
| Vin | Input voltage |
| R1 | Resistor between the input and the output tap |
| R2 | Resistor between the output tap and ground |
Edge cases worth knowing
Vout is always measured across R2, not R1 — swapping which resistor is “R1” and which is “R2” flips the output voltage to a different value, so wiring orientation matters.
Both resistors at zero makes the ratio undefined — there’s no meaningful divider with no resistance in the circuit at all.
Frequently asked questions
What’s a voltage divider used for?
Scaling a voltage down to a lower level, commonly for sensor interfacing or reference voltages in electronics circuits.
Why does the output depend on the ratio of resistors, not their absolute values?
Because the divider formula only involves R2 divided by the sum of both resistors — doubling both resistances proportionally leaves the output voltage unchanged.
What happens if I swap R1 and R2?
The output voltage changes to reflect the fraction across the other resistor — swapping effectively inverts which portion of the input voltage you’re measuring.
