Circuit Diagram
Voltage division across R1 and R2
Use our free online voltage divider calculator to calculate output voltage, input voltage, or resistor values. This resistor divider calculator works with any voltage divider circuit and provides instant results using the standard voltage divider formula.
You can also use this calculator to provide any 3 known values in the circuit and calculate the 4th one.
Here:
- Vin is the input voltage
- R1 is the resistance of the 1st resistor,
- R2 is the resistance of the 2nd resistor,
- Vout is the output voltage.
Quick Reference
- Formula: Vout = (Vin × R2) / (R1 + R2)
- Current: I = Vin / (R1 + R2)
- Power: P = I² × R or V² / R
- Power across R1 = I² × R1
- Power across R2 = I² × R2
How to use this Voltage Divider Calculator?
Our Voltage Divider Calculator helps you to determine the perfect resistor values or voltages for your circuit. Follow these simple step to use our voltage divider calculator
Choose Your Known Values
The calculator has four fields namely, Input Voltage (Vin), Resistance 1 (R1), Resistance 2 (R2), and Output Voltage (Vout). Out of these four values, the user has to input at least 3 values. When you click on calculate, the calculator will automatically compute the fourth value for you
Pay Attention to Units
Please pay attention to the unit. For Voltages use Volts (V). For resistance choose between Ohms (Ω), Kilohms (kΩ), or Megaohms (MΩ).
How Does Voltage Divider Calculator Work?
A potential divider circuit is a very common circuit used in electronics where an input voltage has to be converted to another voltage less than it. This circuit is very useful for all analog circuits where variable voltages are required, hence it is important to understand how this circuit works and how to calculate the values of Resistors.
A voltage divider circuit is very simple circuit consisting of only two resistors (R1 and R2) as shown above. The required output voltage (Vout) can be obtained across the resistor R2. Using these two resistors we can convert an input voltage to any required output voltage, this output voltage is decided by the value of the resistance R1 and R2. The formulae to calculate Vout is shown below.
Vout= (Vin x R2) / (R1 + R2)Where, Vout= Output Voltage Vin=Input Voltage and R1=Upper Resistor R2=Lower resistor
We can use the above voltage divider calculator to calculate any one of the value mentioned in the voltage divider formulae, but now let us learn how this formulae was derived. Consider the below circuit which can be used to convert 5V input to 3.3V output for analysis
To understand how a potential diver formula is derived we need Ohms law calculator , according to Ohms law the voltage drop across any location is a product of the current flowing through the circuit and the Resistance across it.
Voltage = Current Flowing through × Resistance across the voltage
Let us use this to calculate the Input Voltage (Vin) for the above circuit. Here there are two resistors across input voltage Vin, hence
Input Voltage = Current × (Resistance 1 + Resistance 2)
Vin = I × (R1 + R2) (1)Similarly let us calculate for output voltage (Vout), here there is only one resistor (R2) across it hence
Output Voltage = Current × Resistance R2
Vout = I × R2 (2)If we look at the equation 1 and 2 we can notice that the value of current is same, hence lets re-write
Equation 1 as, I = Vin / (R1 + R2)
Equation 2 as, I = Vout /R2
Since the current flowing through the circuit is constant, the current I will remain same for both the equations hence we can equate them as
Vin / (R1 + R2) = Vout /R2
Vout= (Vin x R2) / (R1 + R2)Voltage Divider Current Calculator
This voltage divider calculator also helps you calculate the current flowing through the circuit. The current in a voltage divider circuit is the same through both resistors since they are in series.
Current Calculation Formula
Current (I) = Vin / (R1 + R2)
Power Consumption Calculation
Total Power = I² × (R1 + R2) or Vin² / (R1 + R2)
Power across R1 = I² × R1
Power across R2 = I² × R2
Voltage Divider Calculator Examples
Example 1: 5V to 3.3V Conversion (Microcontroller Applications)
Input: Vin = 5V, R1 = 1kΩ, R2 = 2kΩ
Calculation: Vout = (5 × 2000) / (1000 + 2000) = 10000 / 3000 = 3.33V
Current: I = 5V / (1kΩ + 2kΩ) = 1.67mA
Application: Perfect for Arduino 5V to 3.3V logic level conversion
Example 2: Battery Voltage Monitoring
Input: 9V battery, desired output = 4.5V, R1 = 10kΩ
Required R2 = 10kΩ (equal resistor values give half voltage)
Vout = (9 × 10000) / (10000 + 10000) = 4.5V
Current: I = 9V / 20kΩ = 0.45mA (low power consumption)
Example 3: LED Current Limiting Circuit
Input: 12V supply, LED forward voltage = 2V, desired current = 20mA
Required voltage drop = 12V - 2V = 10V
Current limiting resistor = 10V / 0.02A = 500Ω
Power rating needed = 10V × 0.02A = 0.2W (use 0.25W resistor)
Common Application with Solutions
Let's consider a common application in microcontroller circuits where the input voltage (Vin) is 5V and the desired output voltage (Vout) is 3.3V. If we fix the value of R1 at 1kΩ, which is a commonly available resistor, and click on calculate the resulting value for resistor R2 is 1.94kΩ. Now practically we will not have a resistor with value 1.94kΩ so we will use the closest available resistor which 2kΩ
One more common application is in battery voltage division, say we have a 9V battery and our desired output voltage is 5V. Then our Vin is 9V and Vout is 5V. Again if we fix the value of R1 at 4.7kΩ and calculate using this voltage divider resistor calculator, the resulting output for R2 will be R2 = 6.8kΩ. In this case the resistor 6.8kΩ itself is available so we can directly use it.
Power Rating Considerations
Another important factor to consider while selecting the resistor values is its power rating (P). Once you know the values of I (based on load), Vin, R1, and R2, add R1 and R2 together to get RTOTAL and use the Ohms law calculator to find out the power(Watts) rating required for the resistors. Or simply use the formulae P=VI to decide on the power rating for your resistor. If a proper Power rating is not selected the resistor will overheat and might also burn.
Tips for Accurate Results
This online voltage divider calculator is highly reliable for a wide range of calculations and applications. But here are few tips to make sure we get the most accurate results not just on the calculator but also when you actually build the circuit practically.
Voltage Constraints: The input voltage must be greater than the output voltage and all values must be positive number. The maximum voltage should not be more than 1000V for safety purposes
Resistance Selection: Always use standard resistor values when possible. Consider resistor tolerance (1% or 5%) in your final output, lower tolerance resistor will practically give close to the expected results. Also, remember that higher resistance values reduce power consumption and lower resistance values increase power consumption but provide better stability.
Common Mistakes to Avoid: Don't forget to match units and consider power dissipation. Consider the output power requirement of your load and make sure the your resistance can handle the current required for your load. Remember temperature effects, if the resistor gets hot its resistance value will drop resulting in a different output voltage.
Related Electronics Calculators
For complete circuit design, you might also need these related online electronics calculators:
- Ohms Law Calculator - Calculate voltage, current, resistance, and power
- Resistor Color Code Calculator - Identify resistor values
- LED Resistor Calculator - Calculate current limiting resistors
Voltage Divider vs Other Circuits
Unlike current divider circuits that split current, voltage dividers split voltage proportionally. For AC applications, consider using capacitive voltage dividers instead of resistive ones.
Frequently Asked Questions
What is a voltage divider calculator used for?
A voltage divider calculator is used to determine the output voltage in a resistive voltage divider circuit. It helps engineers and hobbyists calculate resistor values needed to achieve a specific voltage output from a higher input voltage, commonly used in sensor circuits, reference voltages, and logic level conversion.
How accurate is this voltage divider calculator?
Our voltage divider calculator provides theoretical accuracy up to 6 decimal places. However, practical accuracy depends on resistor tolerance (typically ±1% to ±5%), temperature effects, and load current. For precision applications, use 1% tolerance resistors and consider the load impedance effects.
Can I use this calculator for AC voltage dividers?
This calculator is designed for DC voltage dividers using resistors. For AC applications, you'll need to consider impedance rather than just resistance, especially with capacitive or inductive components. The basic voltage division principle remains the same for AC resistive circuits.
What happens if I don't consider the load current?
Ignoring load current is the most common mistake in voltage divider design. When current flows to your load, it affects the output voltage. For accurate results, ensure your load impedance is at least 10 times higher than R2, or use our current calculations to account for loading effects.
Why is my calculated voltage different from measured voltage?
Differences between calculated and measured voltages typically occur due to: resistor tolerance (±5% can cause significant variations), temperature effects, load current drawing additional current, or multimeter input impedance affecting the measurement. Use precision resistors for critical applications.
Can this voltage divider calculator handle high voltage applications?
Yes, but exercise extreme caution with high voltages above 50V. Ensure proper power ratings for resistors, consider safety margins, and use appropriate safety measures. The calculator works for voltages up to 1000V, but always follow electrical safety protocols for high voltage work.
This online voltage divider calculator is the most accurate tool for voltage divider circuit analysis. Whether you need a simple voltage divider calc or complex resistor divider calculations, our calculator handles all scenarios with precision.
