Voltage Calculator
Calculate voltage, current, resistance, and power using Ohm's Law and Watt's Law. Enter any two known values to instantly solve for the missing variables. Perfect for electrical engineers, students, and DIY electronics projects.
What Is Ohm's Law?
Ohm's Law is a fundamental principle in electrical engineering that describes the relationship between voltage, current, and resistance. It states that the current through a conductor between two points is directly proportional to the voltage across the two points and inversely proportional to the resistance.
V = I × R
Where:
V = Voltage (volts)
I = Current (amperes)
R = Resistance (ohms)
This calculator also uses Watt's Law (P = V × I) to calculate power, and includes a voltage divider calculator for series resistor circuits.
How Does the Voltage Calculator Work?
The calculator supports three modes:
- Ohm's Law: Enter any two of voltage, current, or resistance to calculate the third.
- Watt's Law: Enter any two of voltage, current, or power to calculate the third.
- Voltage Divider: Enter input voltage, R1, and R2 to calculate the output voltage.
All results include the power calculation (P = V × I) and can be displayed in different unit scales (standard, milli, kilo, mega).
Why Use This Voltage Calculator?
- Three Modes: Ohm's Law, Watt's Law, and Voltage Divider.
- Unit Flexibility: Choose from standard, milli, kilo, or mega scales.
- Complete Results: Calculate voltage, current, resistance, and power simultaneously.
- Power Factor: Optional power factor for AC circuit calculations.
- Free & Private: No registration, no data storage.
Understanding Electrical Units
- Volt (V): The unit of electrical potential difference.
- Ampere (A): The unit of electrical current.
- Ohm (Ω): The unit of electrical resistance.
- Watt (W): The unit of electrical power.
- Power Factor (PF): The ratio of real power to apparent power in AC circuits.
❓ Voltage Calculator FAQ
What is Ohm's Law?
Ohm's Law states that the voltage across a conductor is equal to the current through it multiplied by its resistance: V = I × R.
What is Watt's Law?
Watt's Law states that power is equal to voltage multiplied by current: P = V × I. It is used to calculate electrical power in a circuit.
How do I use the Ohm's Law mode?
Enter any two of the three values (voltage, current, or resistance) and leave the third blank. The calculator will solve for the missing value.
What is a voltage divider?
A voltage divider is a simple circuit that produces an output voltage that is a fraction of the input voltage. It consists of two resistors in series. The output voltage is Vout = Vin × R2 ÷ (R1 + R2).
What is the difference between AC and DC?
DC (Direct Current) flows in one direction with constant voltage. AC (Alternating Current) periodically reverses direction and varies in magnitude. This calculator works for both, with an optional power factor for AC.
What is power factor?
Power factor is the ratio of real power to apparent power in AC circuits. It ranges from 0 to 1. A power factor of 1 indicates all power is being used effectively. Typical values are 0.7-0.95 for AC motors and electronics.
How do I calculate power from voltage and current?
Power = Voltage × Current (P = V × I). For AC circuits, multiply by the power factor: P = V × I × PF.
What units does this calculator use?
The calculator supports standard units (V, A, Ω, W), milliunits (mV, mA, mΩ, mW), kilounits (kV, kA, kΩ, kW), and megaunits (MV, MA, MΩ, MW).
What is the relationship between voltage, current, and resistance?
Voltage equals current times resistance (V = I × R). Current equals voltage divided by resistance (I = V ÷ R). Resistance equals voltage divided by current (R = V ÷ I).
Can I use this calculator for AC circuits?
Yes. The calculator includes a power factor option for AC circuit calculations. For DC circuits, use a power factor of 1.0.
What is the voltage divider formula?
Vout = Vin × R2 ÷ (R1 + R2). This calculates the output voltage across R2.
How do I calculate voltage drop across a resistor?
Voltage drop = Current × Resistance (V = I × R). This calculator can determine voltage, current, or resistance given the other two.
What is the difference between voltage and current?
Voltage is the electrical potential difference between two points (the "push" that drives current). Current is the flow of electrical charge (the "flow" itself).
How do I calculate resistance from voltage and current?
Resistance = Voltage ÷ Current (R = V ÷ I). Use the Ohm's Law mode and enter voltage and current to calculate resistance.
What is the SI unit of voltage?
The SI unit of voltage is the volt (V), named after Alessandro Volta. One volt is defined as the potential difference that drives one ampere of current through one ohm of resistance.
Is this calculator free to use?
Yes, this calculator is completely free to use. No registration or personal data storage is required. All calculations are performed in your browser.
What is the difference between a voltage divider and a current divider?
A voltage divider uses series resistors to divide voltage. A current divider uses parallel resistors to divide current. This calculator focuses on the voltage divider.