Voltage Divider Calculator
Enter an input voltage and two resistances and get the output voltage in volts — the single number that tells you how far two resistors drop a supply and what fraction reaches your circuit.
Voltage and resistors in, output out
Enter the input voltage in volts and the two resistances in ohms and the calculator returns the output voltage measured across R₂.
Mind which is R₂
R₂ is the bottom resistor, the one the output is measured across. Swapping R₁ and R₂ changes the result.
What is a voltage divider calculator?
Two resistors, one stepped-down voltage
A voltage divider calculator turns three measurements — the input voltage and the two resistances in a simple series chain — into a single number: the output voltage, the slice of the supply that appears across the lower resistor. Two resistors in series share a voltage in proportion to their sizes, so tapping the node between them gives a smaller, predictable voltage. That makes the divider the simplest way to drop a higher voltage to a usable level, read a sensor, or set a reference, and the go-to first circuit for anyone scaling a signal down.
Enter the input voltage in volts and the two resistances in ohms to get the output voltage instantly.
One short formula: scale the input by the fraction of resistance below the output node.
Vout = Vin × R₂ ÷ (R₁ + R₂)The fraction R₂ ÷ (R₁ + R₂) is the share of the total resistance that sits below the output node, and the output voltage is exactly that share of the input. Keep the input in volts and both resistances in the same unit — ohms here — and the output comes out in volts. The resistor values can be in kilohms or megohms instead, as long as both use the same unit, because they only ever appear as a ratio.
Suppose a 12 V supply feeds a divider with R₁ = 1 kΩ on top and R₂ = 2 kΩ on the bottom.
Note the input and resistors
Input voltage is 12 V, with R₁ = 1000 Ω and R₂ = 2000 Ω — the output is measured across R₂.
Find the resistance fraction
R₂ ÷ (R₁ + R₂) = 2000 ÷ 3000 = two thirds of the supply.
Read the output voltage
12 × 2000 ÷ 3000 = 8 V — two thirds of the 12 V supply reaches the output.
The single output figure tells a clear story about how your two resistors split the supply. The key insight is that the output is purely a fraction of the input — the fraction R₂ ÷ (R₁ + R₂) — so it depends on the ratio of the resistors, not their absolute size. Two 1 kΩ resistors and two 1 MΩ resistors both halve the voltage; the larger pair simply draws less current. When R₁ and R₂ are equal the fraction is one half, so the output is exactly half the input; making R₂ larger relative to R₁ pushes the output up toward the full supply, while making R₁ larger drags it down toward zero. One caution shapes every real design: this is the unloaded output. Whatever you connect to the output node sits in parallel with R₂ and lowers the voltage, an effect that is negligible when the load resistance is far larger than R₂ but serious when it is comparable. Read your result as the best case, then keep R₂ small enough relative to the load that the loaded voltage stays close to it.
The formula is exact, but a couple of practical points are worth keeping in mind.
Loading, tolerances, and current draw
The formula gives the unloaded output — connecting a real load in parallel with R₂ lowers it, so size R₂ well below the load resistance. Resistor tolerances (often ±1 % to ±5 %) shift the output, and very large resistances make the node sensitive to stray current and noise. A divider also wastes power as continuous current flows through both resistors, so it is unsuitable as a power supply for anything that draws meaningful current — use a regulator there instead.