Voltage Divider Calculator
Find the output voltage of a two-resistor voltage divider from the supply voltage and both resistor values. Optionally add a load to see the loading effect and drop in output voltage.
V
Ω
Ω
Ω
Unloaded output — no load connected
- 1
Total resistance R1 + R2
10,000 + 4,700 = 14,700 - 2
Output voltage Vₒᵤₜ
12 × 4,700 ÷ 14,700 = 3.8367The output is the fraction of Vin that appears across R2.
How does this calculator work?
Voltage divider output: Vₒᵤₜ = Vᵢₙ × R2/(R1+R2) (unloaded). With a load Rₗ, replace R2 with R2∥Rₗ = R2·Rₗ/(R2+Rₗ). Quiescent current = Vᵢₙ/(R1+R2); Thevenin resistance = R1∥R2. Keep R2 at least 10× smaller than the load to limit the output voltage drop to under 10 %.
Formula
How this is calculated
A voltage divider is the simplest resistor circuit: R1 connects the supply Vᵢₙ to the output node, and R2 connects the output node to ground. Because the same current flows through both resistors (Kirchhoff's current law with no load attached), the voltage across R2 — and therefore the output — is Vₒᵤₜ = Vᵢₙ × R2 / (R1 + R2). Making R2 larger relative to R1 raises the output fraction; equal resistors give exactly half the supply.
In practice, connecting a load resistor Rₗ across R2 creates a parallel combination (R2 ∥ Rₗ) that is smaller than R2 alone, so the output drops below the unloaded value. The loaded formula replaces R2 with (R2·Rₗ)/(R2+Rₗ). This loading effect is minimised when Rₗ is much larger than R2 (rule of thumb: Rₗ ≥ 10·R2 keeps the error below 10 %).
The Thevenin resistance Rₜₕ = R1 ∥ R2 characterises the divider's output impedance. A lower Rₜₕ means the divider behaves more like an ideal voltage source and the output is less sensitive to load changes. The quiescent current through R1 and R2 equals Vᵢₙ / (R1 + R2) and flows regardless of load, so keep it small to save power but large enough to dominate any stray load current.
Frequently asked questions
The load sits in parallel with R2, reducing the effective resistance at the output node. This means a larger fraction of Vᵢₙ now drops across R1 and less is available at the output. The effect is proportional to how close Rₗ is to R2 — a load ten times larger than R2 causes about a 9 % drop.
The Thevenin (output) resistance equals R1 and R2 in parallel: Rₜₕ = R1·R2/(R1+R2). Any load sees the divider as an ideal voltage source Vₒᵤₜ (unloaded) in series with Rₜₕ. A low Rₜₕ means the divider can supply load current with minimal voltage drop, making the output more stable.
First pick a quiescent current (typically 10–100× the expected load current to minimise loading). The sum R1 + R2 = Vᵢₙ / I_quiescent. Then R2 = (Vₒᵤₜ / Vᵢₙ) × (R1 + R2) gives R2, and R1 = (R1 + R2) − R2. Use the nearest standard (E24 or E96) resistor values and check the result with this calculator.
Also known as
TG we-Calculate Editorial Team. (2026). Voltage Divider Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/voltage-divider-calculator
TG we-Calculate Editorial Team. "Voltage Divider Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/voltage-divider-calculator.
TG we-Calculate Editorial Team, "Voltage Divider Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/voltage-divider-calculator
@misc{wecalculate_voltage_divider_calculator, title = {Voltage Divider Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/voltage-divider-calculator}}, year = {2026}, note = {TG we-Calculate} }
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