Voltage Divider Calculator
Enter any three values from your circuit and instantly solve for the fourth. Get nearest standard resistor values, current draw, and power dissipation. Nothing uploaded.
Learn more: voltage dividers and resistor networks
How voltage dividers work and why they matter
A voltage divider is a simple two-resistor circuit that reduces a voltage to a lower value proportional to the resistor ratio. Input voltage multiplied by (R2 divided by R1 plus R2) equals output voltage. This is essential for sensor circuits, audio circuits, and anywhere you need to reduce voltage safely. The calculator works both ways: give it the desired output voltage and it calculates the resistor ratio needed.
Load impedance and why it matters for accuracy
Voltage dividers assume the output is connected to a high-impedance input (or no load). If you connect a low-impedance load (like an LED or speaker), the actual output voltage drops because current flows through R2 and the load in parallel. The calculator lets you specify the load impedance so it can calculate the actual output voltage under real-world conditions.
Choosing resistor values: tolerance, power rating, and practical limits
Resistor values come in standard series (E12, E24, E96) with 5-20 percent tolerances. The calculator suggests the closest standard resistor values and their accuracy. Power rating depends on expected current - for low-current circuits (milliamps), 1/4 watt resistors are typical. For audio circuits carrying amps, power rating must be higher to avoid heat damage.
FAQ
What is a voltage divider circuit?
A voltage divider uses two resistors in series to reduce voltage. The output is taken from between the resistors. Output voltage equals input voltage times (R2 divided by R1 plus R2). This simple circuit is used everywhere in electronics for sensor conditioning and signal scaling.
How do I calculate resistor values for a voltage divider?
Divide the desired output voltage by the input voltage to get the ratio. Choose a standard resistor for R1, then calculate R2 as R1 times the ratio divided by (1 minus the ratio). The calculator does this instantly.
Does load impedance affect voltage divider output?
Yes. If a load is connected to the output, it draws current through R2, lowering the output voltage below the theoretical value. Specify the load impedance in the calculator to see the real-world output voltage.