Voltage Divider
Output voltage of a two-resistor divider, or the resistor that gives the output you want — with the load across the output taken into account, not ignored.
The output voltage open-circuit and under load, the resistor value to design for, the current and power in each part, and the divider’s output resistance.
Example: 12 V across 10 kΩ and 4.7 kΩ gives 3.84 V open-circuit — but 2.91 V with a 10 kΩ load. For 3.3 V from 5 V with R₁ = 1 kΩ, R₂ = 1,941 Ω.
A ratio,
until something is connected.
The divider formula, why the load matters, how the design mode solves for a resistor, and what ideal parts leave out.
The divider
Two resistors in series across V_in carry the same current, so the voltage across the lower one is V_out = V_in × R₂ ÷ (R₁ + R₂). The current drawn from the source is V_in ÷ (R₁ + R₂) and each resistor dissipates I²R. The Thevenin output resistance is R₁ ∥ R₂ — the figure that decides how much any load will disturb the output.
With a load
A load R_L across the output sits in parallel with R₂, so the divider really is R₁ against R₂ ∥ R_L and the output falls. This page computes that exactly rather than assuming the load is negligible, and reports how far the output moves from its open-circuit value. When the drop matters, lower both resistors (more current, less output resistance) or buffer the output — a divider is a reference, not a supply.
Design mode
Given V_in, the wanted V_out and one resistor, the other follows from the same equation: R₂ = R₁ × V_out ÷ (V_in − V_out), or R₁ = R₂ × (V_in − V_out) ÷ V_out. With a load, the lower leg that must appear is R₂ ∥ R_L, so R₂ = 1 ÷ (1/leg − 1/R_L); if the load alone is already below the required leg no R₂ can reach the target and the page says so. Results are exact values for you to round to stock parts.
What the number does not settle
Resistors are ideal and at nominal value; tolerance, temperature coefficient and self-heating are not modelled, and a divider does not regulate — the output follows V_in. Power ratings are the manufacturer's for the parts you use. Inputs stay in your browser; the same four anonymous usage counts as the rest of the site apply.