Voltage Divider Calculator

Voltage Divider Calculator supports engineering calculations with transparent assumptions, practical result interpretation, and links to next-step technical resources.

Divider Visualization

Formula

No load: Vout = Vin x R2 / (R1 + R2)

With load: Vout = Vin x (R2||RL) / (R1 + (R2||RL))

R2||RL = (R2 x RL) / (R2 + RL)

Circuit

Voltage Ratio

Enter Vin, R1, and R2 to render divider output.

Inputs & Outputs

Voltage Input (Vin)

1st Resistance (R1)

2nd Resistance (R2)

Under Load

Output

Output Voltage (No Load)

Output Voltage (Loaded)

Source Current

Source Power

Load Power

Load Efficiency

Equivalent Bottom Resistance

Voltage Divider Fundamentals

Divider output is set by resistance ratio. When load is connected, effective bottom resistance changes, so the no-load equation is no longer accurate.

No Load

Vout = Vin x R2 / (R1 + R2)

I = Vin / (R1 + R2)

Use for open-circuit outputs and very high-impedance measurement nodes.

With Load

Rbottom = R2||RL

Vout = Vin x Rbottom / (R1 + Rbottom)

Required for real outputs driving finite impedance loads.

Quick Divider Ratio Reference

Common resistor ratio patterns for quick front-end scaling and threshold design.

R1:R2 Ratio	Relationship	Vout / Vin	Typical Use
1:1	R1 = R2	50%	Midpoint reference and ADC biasing
1:2	R1 = 2 x R2	33.33%	3.3 V sensing from higher rails
2:1	R1 = 0.5 x R2	66.67%	Threshold and comparator scaling
9:1	R1 = 9 x R2	10%	High-voltage monitor front-end
19:1	R1 = 19 x R2	5%	Large attenuation for measurement inputs

Design Selection Matrix

Match divider strategy to measurement accuracy, impedance constraints, and power budget.

Scenario	Key Goal	Recommendation	Critical Checks
Voltage sensing / ADC input scaling	Accurate ratio and low loading error	Use higher-value divider with known ADC input impedance or buffer stage.	Tolerance, tempco, sampling capacitor kickback
Reference generation / comparator threshold	Stable threshold over temperature	Match resistor technology and keep thermal coupling consistent.	Drift, noise, hysteresis margin
Power divider with load branch	Deliver usable load power	Model RL explicitly; no-load formula is not sufficient.	Efficiency, resistor wattage, source current budget