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Free online voltage divider calculator. Quickly calculate output voltage from input voltage and two resistor values. Ideal for electronics DIY, repairs, and education.
Enter input voltage and resistor values to see results.
Overview
Understand what the tool solves, how it works, and the boundaries of its data.
This voltage divider calculator models a source voltage across two series resistors. Enter the input voltage (Vin), the upper resistor (R1), and the lower resistor (R2). The output tap is between the resistors, with Vout measured across R2 and the lower reference node.
Vout = Vin × R2 ÷ (R1 + R2)
I = Vin ÷ (R1 + R2); Rtotal = R1 + R2
Ptotal = Vin² ÷ (R1 + R2)
R1 and R2 must use the same resistance unit; ohms (Ω) with volts (V) produce amperes (A), which the tool displays as milliamperes (mA). The total power output is the combined dissipation of both resistors in this ideal model, displayed in milliwatts (mW).
Guide
Follow the workflow and verify inputs and outputs with practical examples.
Use the voltage applied across the complete series pair. A negative voltage is accepted and gives a signed output under the same ideal model.
Enter numeric R1 and R2 values in the same unit. Zero is allowed for one resistor, but their sum must be greater than zero.
Vout is the voltage across R2. Current is the series current through both resistors. Total resistance is R1+R2, and total power is for the pair together.
Example: with Vin = 5 V, R1 = 1,000 Ω, and R2 = 2,000 Ω, the denominator is 3,000 Ω. Vout = 5 × 2,000 / 3,000 = 3.33 V; current = 5 / 3,000 A = 1.67 mA; total power = 25 / 3,000 W = 8.33 mW. These values reproduce the displayed calculation before rounding.
Use cases
See how the tool fits into real work and everyday tasks.
Enter the stated source and resistor values, then compare the output voltage and series current with a hand calculation.
Keep Vin fixed while trying alternative R1/R2 pairs to see how their ratio changes the ideal output and current draw.
Q&A
Find concise answers to common questions and confusing cases.
No. It assumes the output is unloaded, so the connected device draws no current from the midpoint. A real load in parallel with R2 changes the effective lower resistance and usually changes Vout.
No. It is the combined power for the two-resistor string. The tool does not report each resistor’s dissipation or check component ratings. Calculate each drop and power separately, then compare with the parts’ ratings and design margins.
All three fields need numeric values, both resistors must be nonnegative, and their sum must be positive. Clear the fields with Reset if you want to start over.
Notes
Review scope, result limitations, and important precautions before use.
This is an ideal DC two-resistor calculation. It does not model a connected load, resistor tolerance, source resistance, temperature effects, noise, frequency response, or transient behavior. A divider can drop a signal voltage, but this result alone does not show that it can safely or reliably power a device. Verify individual resistor dissipation, voltage ratings, tolerances, and the load’s input requirements in the actual circuit before selecting components.
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