Ohm's Law Calculator
Calculate voltage, current, resistance, or power from any two known electrical values. Select your known pair, enter the values with optional SI prefixes (k, m, μ, n), and the Ohm's Law calculator instantly computes the remaining quantities — all running locally in your browser with no signup required.
Select any two known electrical quantities and the Ohm's Law calculator instantly computes the remaining two. Supports SI prefixes (k, m, μ, n) for all inputs. All calculations run locally in your browser — no signup required.
Ohm's Law Reference
SI Prefix Guide
Type values like 4.7k, 220u, 2.2m
All calculations run locally in your browser. No data is ever sent to a server.
Why Use Our Ohm's Law Calculator?
Instant, accurate, and private electrical calculations — entirely in your browser
Instant Ohm's Law Calculation
Select any two known electrical quantities and the Ohm's Law calculator computes the remaining two instantly — no submit button needed. Results update in real time as you type, with full SI prefix support.
Secure Ohm's Law Calculator Online
Your circuit values and calculations never leave your device. The Ohm's Law calculator runs 100% client-side in your browser — no server, no account, no data collection of any kind.
Ohm's Law Calculator — No Installation
Use the Ohm's Law calculator directly in any modern browser with no downloads, no plugins, and no account required. Works on desktop and mobile — open the page and start calculating immediately.
100% Free with All 6 Formula Combinations
The Ohm's Law calculator is completely free with no signup, no usage limits, and no ads. Solve for any unknown from any two known values — all 6 combinations of V, I, R, and P are supported.
Common Use Cases for Ohm's Law Calculator
Who uses the Ohm's Law calculator and why
Electronics Hobbyists and Makers
Use the Ohm's Law calculator to quickly find the correct resistor value for an LED circuit, calculate the current draw of a component, or verify that a power supply can handle a given load — without doing the math by hand.
Electrical Engineering Students
Students use the Ohm's Law calculator to check their circuit analysis homework, verify textbook answers, and build intuition for how voltage, current, resistance, and power relate to each other in DC circuits.
PCB and Circuit Design
PCB designers use the Ohm's Law calculator to size current-limiting resistors, calculate trace current capacity, and verify power dissipation in components before committing to a board layout.
Automotive and 12V Systems
Automotive technicians and 12V system builders use the Ohm's Law calculator to size fuses, calculate wire gauge requirements, and determine the power draw of accessories like lights, amplifiers, and motors.
Solar and Battery Systems
Off-grid and solar system designers use the Ohm's Law calculator to calculate charge controller settings, battery discharge rates, and cable sizing for 12V, 24V, and 48V systems.
Teaching and Classroom Use
Physics and electronics teachers use the Ohm's Law calculator to demonstrate the relationship between V, I, R, and P in real time during lessons. The formula reference triangle makes the relationships visually clear.
Understanding Ohm's Law
The physics behind the Ohm's Law calculator and how to apply it
What is Ohm's Law?
Ohm's Law states that the voltage (V) across a conductor is directly proportional to the current (I) flowing through it, with the constant of proportionality being the resistance (R). The fundamental equation is V = I × R. Combined with the power equation P = V × I, this gives 12 interrelated formulas that let you calculate any one of the four quantities — voltage, current, resistance, or power — from any two known values. Our Ohm's Law calculator online implements all 6 input combinations and displays results with SI prefix notation (kΩ, mA, μW, etc.) for easy reading.
How Our Ohm's Law Calculator Works
- Select Your Known Values: Choose which two quantities you know from the six selector buttons — Voltage + Current, Voltage + Resistance, Voltage + Power, Current + Resistance, Current + Power, or Resistance + Power.
- Enter Your Values:Type your known values into the two active input fields. The Ohm's Law calculator supports SI prefixes — type
4.7kfor 4,700 Ω,220ufor 220 μA, or2.2mfor 2.2 mΩ. Results update instantly as you type. - Read All Four Results: The calculator displays all four quantities — voltage, current, resistance, and power — in both SI prefix notation and raw decimal form. The formula reference panel shows which equations were used. All calculations run locally in your browser with no data sent to any server.
The 12 Ohm's Law Formulas
- Voltage (V):V = I × R | V = P / I | V = √(P × R)
- Current (I):I = V / R | I = P / V | I = √(P / R)
- Resistance (R):R = V / I | R = V² / P | R = P / I²
- Power (P):P = V × I | P = I² × R | P = V² / R
Important Limitations of Ohm's Law
Ohm's Law applies to ohmic (linear) conductors — resistors, wires, and other components where resistance remains constant regardless of voltage or current. It does notapply directly to non-ohmic components such as diodes, transistors, LEDs, and capacitors, where the V-I relationship is non-linear. For AC circuits, impedance (Z) replaces resistance (R), and the relationship becomes more complex due to phase differences between voltage and current. The Ohm's Law calculator is designed for DC circuit analysis with purely resistive components.
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Frequently Asked Questions About Ohm's Law Calculator
Common questions about Ohm's Law and how to use the calculator
An Ohm's Law calculator is a tool that computes any unknown electrical quantity — voltage (V), current (I), resistance (R), or power (P) — from any two known values using Ohm's Law (V = I × R) and the power equation (P = V × I). Our Ohm's Law calculator online runs entirely in your browser, updating results in real time. No signup, no server, no data collection.
Absolutely. The Ohm's Law calculator runs 100% client-side in your browser. Your circuit values and calculations are never transmitted to any server, stored in a database, or tracked in any way. Everything stays completely private on your device.
Yes — the Ohm's Law calculator is 100% free with no signup, no account, and no usage limits. Calculate as many circuits as you need, completely free forever. There are no ads, no premium tiers, and no data collection.
Ohm's Law states that voltage (V) equals current (I) multiplied by resistance (R): V = I × R. Combined with the power equation P = V × I, this gives 12 formulas that relate all four electrical quantities. The Ohm's Law calculator applies the correct formula automatically based on which two values you provide.
Yes. The Ohm's Law calculator supports SI prefix notation for all inputs. Type 4.7k for 4,700 Ω, 220u or 220μ for 220 μA, 2.2m for 2.2 mΩ, 1M for 1 MΩ, and so on. Results are also displayed in SI prefix notation (kΩ, mA, μW, etc.) for easy reading.
Ohm's Law in its basic form (V = I × R) applies to DC circuits with purely resistive components. For AC circuits, resistance is replaced by impedance (Z), which includes the effects of capacitance and inductance. The Ohm's Law calculator is designed for DC resistive circuit analysis.
No — LEDs and diodes are non-ohmic components, meaning their resistance changes with voltage and current. Ohm's Law cannot be applied directly to them. However, you can use the Ohm's Law calculator to calculate the current-limiting resistor needed in series with an LED: R = (Supply Voltage − LED Forward Voltage) / Desired Current.
Power (P) is the rate at which electrical energy is consumed or produced. The three power formulas derived from Ohm's Law are: P = V × I (power equals voltage times current), P = I² × R (power equals current squared times resistance), and P = V² / R (power equals voltage squared divided by resistance). The Ohm's Law calculator computes power automatically alongside V, I, and R.
Yes. The Ohm's Law calculator is fully responsive and works on all modern mobile browsers. The selector buttons, input fields, and results panel all adapt to smaller screens. You can calculate circuit values on any device without installing an app.