Ohm’s Law Calculator — Instantly calculate voltage (V), current (I), resistance (R), and power (P) for electronics and physics. Modern, interactive UI. Mobile-optimized, SEO-rich, and privacy-first. All calculations run instantly in your browser—no data leaves your device.
How to Use the Ohm’s Law Calculator
- Select Calculation Type
Choose the value you want to calculate from the four options: Voltage (V), Current (I), Resistance (R), or Power (P).
- Enter Your Data
Input the two known values required for your selected calculation. Ensure you are using the standard SI units: Volts (V), Amperes (A), Ohms (Ω), and Watts (W).
- See Real-Time Results
The calculated answer, the exact formula used, and a clear explanation will appear instantly in the result card as you type.
- Copy or Clear
Use the “Copy” button to save the full result for your notes, or click “Clear” to reset the calculator for a new problem.
Advantages & Limitations of the Ohm’s Law Calculator
Advantages
- Comprehensive: Solves for all four key variables: Voltage, Current, Resistance, and Power.
- Instantaneous: Results appear in real-time as you input data, no clicking required.
- Educational: Always displays the specific formula being used, reinforcing learning.
- 100% Private: All calculations are performed in your browser. No data is ever sent or stored.
- Fully Responsive: A clean, modern interface that works flawlessly on any device.
Limitations
- DC Circuits Only: Designed for Direct Current (DC) circuits. For AC circuits, it only applies to purely resistive components.
- SI Units Required: Does not auto-convert from units like millivolts (mV) or kilo-ohms (kΩ).
- Ideal Conditions: Assumes ideal conductors and resistors, not accounting for factors like temperature changes.
- Single Component Focus: Designed for single-component calculations, not for solving complex series or parallel circuits automatically.
The Ultimate Ohm’s Law Calculator: Mastering V, I, R, & P
Ohm’s Law is the bedrock of electronics and circuit analysis. It is the elegantly simple, yet profoundly powerful principle that describes the relationship between voltage, current, and resistance. For anyone venturing into the world of electronics—be it a student in a physics class, a hobbyist building their first circuit, or a seasoned engineer designing complex systems—a deep, intuitive understanding of Ohm’s Law is non-negotiable.
To aid in this journey, we have created the ultimate Ohm’s Law Calculator. This is more than just a simple calculation tool; it’s an interactive learning platform designed to make the concepts of voltage, current, resistance, and power tangible and easy to manipulate. By allowing you to solve for any of the four variables, it turns abstract formulas into practical, instant answers. This comprehensive guide will break down the core principles of Ohm’s Law, introduce the related Power Law, and demonstrate through practical examples how this calculator is an essential tool for any electronics toolkit.
What is Ohm’s Law? The Foundational Principle
Formulated by German physicist Georg Ohm in 1827, Ohm’s Law states that the current flowing through a conductor between two points is directly proportional to the voltage across the two points. It introduces the concept of resistance as the constant of proportionality.
To make this intuitive, we can use the classic “water in a pipe” analogy:
- Voltage (V) is like the water pressure. It is the potential difference that “pushes” the electricity through the circuit. It is measured in Volts (V).
- Current (I) is like the flow rate of the water. It is the actual flow of electrons through the conductor. It is measured in Amperes (A), or “Amps.”
- Resistance (R) is like the width of the pipe. It is the opposition to the flow of current. A narrow pipe restricts the water flow (high resistance), while a wide pipe allows easy flow (low resistance). It is measured in Ohms (Ω).
Ohm’s Law elegantly connects these three variables in a single, powerful formula.
The Three Faces of Ohm’s Law
The law can be expressed in three algebraic forms, each solving for a different variable. Our Ohm’s Law Calculator allows you to select which variable you want to find and automatically applies the correct formula.
1. Calculating Voltage (V = I × R)
This is the most common expression of the law. It tells you that if you know the current flowing through a resistor and the value of that resistor, you can calculate the voltage “dropped” across it.
Example: An LED circuit has a current of 0.02 Amps (20mA) flowing through a 220 Ohm resistor. To find the voltage across the resistor, you would calculate:
V = 0.02 A × 220 Ω = 4.4 V.
2. Calculating Current (I = V / R)
This form is essential for determining how much current will flow in a circuit. If you know the voltage of your power source and the total resistance, you can find the current.
Example: You connect a 1,000 Ω (1kΩ) resistor to a 9V battery. The current that will flow through the resistor is:
I = 9 V / 1000 Ω = 0.009 A (or 9mA).
3. Calculating Resistance (R = V / I)
This is useful for determining the resistance of an unknown component or for calculating what value of resistor you need in a circuit.
Example: You are testing a circuit and measure that a component has 12V across it and that 0.5A of current is flowing through it. The resistance of that component is:
R = 12 V / 0.5 A = 24 Ω.
Beyond Ohm’s Law: The Critical Role of Power (P)
While Ohm’s Law describes the relationship between V, I, and R, there’s a fourth critical variable in every circuit: Power (P). Power is the rate at which electrical energy is converted into another form, such as heat, light, or motion. It tells you how much work the circuit is doing per second.
The basic formula for electrical power, often called Watt’s Law, is:
P = V × I
- Power (P) is measured in Watts (W).
- Voltage (V) is in Volts.
- Current (I) is in Amps.
This is why our Ohm’s Law Calculator includes a dedicated mode for Power. It’s not just about making a circuit work; it’s about making sure the components can handle the power without burning out. Every resistor has a power rating (e.g., ¼ Watt, ½ Watt). If the calculated power dissipation exceeds this rating, the resistor will fail.
The Power Wheel: All 12 Formulas at a Glance
By combining Ohm’s Law (V=IR) and the Power Law (P=VI), we can derive a total of 12 interconnected formulas. This set of relationships is often visualized in a diagram called the Ohm’s Law Power Wheel. Our calculator handles these relationships implicitly, but understanding them is key to true mastery.
- To Find Power (P): P = VI, P = I²R, P = V²/R
- To Find Voltage (V): V = IR, V = P/I, V = √(P×R)
- To Find Current (I): I = V/R, I = P/V, I = √(P/R)
- To Find Resistance (R): R = V/I, R = P/I², R = V²/P
Practical Applications & Use Cases
This calculator is not just an academic tool; it’s a practical utility for a wide range of real-world tasks.
By integrating the four key variables of any DC circuit into one seamless, interactive tool, the Ohm’s Law Calculator provides the foundation for successful design, diagnosis, and learning in the world of electronics.
Frequently Asked Questions About the Ohm’s Law Calculator
Ohm’s Law specifically describes the relationship between voltage, current, and resistance (`V = I × R`). Watt’s Law (the Power Law) describes the relationship between power, voltage, and current (`P = V × I`). They are two different, but closely related, fundamental laws of electricity. This calculator uses both to provide a complete set of tools.
No, and this is a critical point. Ohm’s Law only applies to ohmic components, which are primarily resistors. Components like diodes, transistors, and LEDs are non-ohmic, meaning their resistance changes as the voltage across them changes. While you can use the law to analyze parts of a circuit containing these components (like the current-limiting resistor for an LED), the law does not describe the behavior of the non-ohmic component itself.
Yes, but with an important caveat. In AC circuits, components like capacitors and inductors introduce a property called reactance, which also impedes current. The total opposition to current in an AC circuit is called impedance (Z), not just resistance. Ohm’s Law can be applied to AC circuits, but it takes the form `V = I × Z`. This calculator is designed for DC circuits, but it works perfectly for the purely resistive parts of an AC circuit (like heaters or incandescent bulbs).
First, use this calculator to find the Power (P) that the resistor will dissipate in your circuit. A safe rule of thumb is to then choose a resistor with a power rating that is at least double the calculated power dissipation. For example, if you calculate that a resistor will dissipate 0.125 Watts (or ⅛ W), you should use a resistor rated for at least 0.25 Watts (¼ W). This safety margin prevents the resistor from overheating and failing.
A resistance of (or close to) zero is called a short circuit. Looking at the formula `I = V / R`, as the resistance `R` approaches zero, the current `I` approaches infinity. In a real circuit, this causes an extremely high current to flow, which will rapidly overheat wires and components, blow fuses, and damage the power supply. This is a dangerous condition that circuit protection devices like fuses and circuit breakers are designed to prevent.
Yes. This calculator uses the base SI units for accuracy. You must convert all values to their base units before entering them.
• 1 milliamp (mA) = 0.001 Amps (A)
• 1 kilohm (kΩ) = 1,000 Ohms (Ω)
• 1 megohm (MΩ) = 1,000,000 Ohms (Ω).
Forgetting this step is one of the most common sources of error in electronics calculations.
Absolutely. 100% of the calculations are performed within your web browser. No data you enter is ever sent to, processed by, or stored on our servers. Your privacy is fully protected.
Yes, this is a completely free tool. There are no fees, subscriptions, or sign-ups required. It is an open educational resource for anyone interested in electronics.