A voltage divider is one of the most fundamental circuits in electronics, using two resistors in series to produce a lower output voltage from a higher input voltage. The formula Vout = Vin × R2 / (R1 + R2) is essential for sensor interfaces, reference voltages, and biasing networks. This calculator finds output voltage, missing resistor values, current draw, and power dissipation instantly.
Enter Circuit Values
Nearest Standard Resistor Values
Circuit Diagram
Enter values and click Calculate to see results
Standard Resistor Values (E12 / E24)
| Series | Values per Decade |
|---|---|
| E12 | 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82 |
| E24 | 10, 11, 12, 13, 15, 16, 18, 20, 22, 24, 27, 30, 33, 36, 39, 43, 47, 51, 56, 62, 68, 75, 82, 91 |
Standard values repeat for each decade: 10–99, 100–999, 1k–9.9k, 10k–99k, 100k–999k, 1M–9.9M, etc.
How to Use the Voltage Divider Calculator
A voltage divider is a simple but essential circuit that reduces a higher voltage to a lower one using two resistors. Whether you are designing a sensor interface, setting a reference voltage, or biasing a transistor, this voltage divider calculator gives you instant results with current draw, power dissipation, and standard resistor suggestions.
Step 1: Choose Your Calculation Mode
The calculator offers two modes. Calculate Vout mode takes your input voltage (Vin) and both resistor values (R1 and R2) to compute the output voltage. Find Resistor mode lets you enter Vin, your desired output voltage, and one known resistor to solve for the missing one. Select the mode that matches your design task.
Step 2: Enter Your Values
Fill in the input voltage and resistor values. Use the unit selectors to choose between ohms, kilohms, or megohms for each resistor. In Find Resistor mode, enter the desired output voltage and leave either R1 or R2 empty. The calculator determines which resistor to solve for automatically.
Step 3: Review Results
Click Calculate to see the output voltage, divider ratio (Vout/Vin), current through the divider (I = Vin / (R1 + R2)), and total power dissipation (P = Vin² / (R1 + R2)). The interactive SVG circuit diagram updates with your actual values so you can visualize the design at a glance.
Standard Resistor Suggestions
When using Find Resistor mode, the calculator suggests the nearest E12 and E24 standard resistor values and shows the resulting Vout for each. This helps you pick a commercially available resistor that gets as close as possible to your target voltage without custom components.
Design Considerations
Keep in mind that an unloaded voltage divider assumes negligible current is drawn from the output node. If your load draws significant current, the actual Vout will be lower than calculated. For power-sensitive designs, use higher resistance values to minimize quiescent current, but watch out for noise susceptibility. For precision applications, consider 1% tolerance resistors from the E24 or E96 series. All calculations run locally in your browser, keeping your design data completely private.
FAQ
Is this voltage divider calculator completely free?
Yes, this calculator is 100% free with no limits. Calculate as many voltage dividers as you need without creating an account or paying anything.
Is my data safe when using this tool?
Absolutely. All calculations run entirely in your browser using client-side JavaScript. No data is sent to any server, stored, or logged. Your values never leave your device.
What is a voltage divider?
A voltage divider is a simple circuit with two resistors in series that produces an output voltage proportional to the input voltage. The formula is Vout = Vin x R2 / (R1 + R2). It is one of the most fundamental circuits in electronics.
How do I choose R1 and R2 for a specific output voltage?
Use the Find Resistor mode in this calculator. Enter your input voltage, desired output voltage, and one known resistor value. The calculator will solve for the missing resistor and suggest the nearest standard E12/E24 value.
What are E12 and E24 resistor series?
E12 and E24 are standard resistor value series. E12 has 12 values per decade (10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82) and E24 has 24 values per decade. Most commercially available resistors come in these standard values.
Does a voltage divider waste power?
Yes, current flows through both resistors continuously, dissipating power as heat. The total power is P = Vin squared / (R1 + R2). Use higher resistance values to reduce waste, but be aware that very high values can make the divider sensitive to load impedance.
Can I use a voltage divider to power a circuit?
A voltage divider works well for low-current applications like sensor references and biasing, but it is a poor choice for powering loads that draw significant current. The output voltage will drop under load because the divider has a relatively high output impedance.
What units does this calculator support?
You can enter resistor values in ohms, kilohms, or megohms using the unit selector next to each input. The calculator handles all unit conversions automatically and displays results with appropriate units.