Ohm's Law & Power Calculator | HaruTools Lab

Lock Parameter: None (Auto) Voltage (V) Current (A) Resistance (Ω) Power (W)

Voltage (V)

Current (A)

Resistance (Ω)

Power (W)

Please enter 2 values (Real-time calculation)

Important Note Regarding Results

This tool calculates theoretical values based on an ideal DC circuit model. In real-world circuits, actual measurements may differ due to factors such as voltage drops across wiring, contact resistance, and changes in resistance caused by component heat.
Exceeding the power rating (wattage) of components (such as resistors) can cause severe overheating or burning hazards. Always design circuits with an adequate safety margin when choosing components.
This website assumes no responsibility for any losses, accidents, or damages arising from the use of calculation results from this tool. For real design and practical work, always verify safety independently and use it at your own risk.

What is the Ohm's Law & Power Calculator?

This tool is an in-browser simulator that instantly calculates "Ohm's Law" and "Electrical Power", the fundamentals of electrical circuits. By simply entering any two known values out of Voltage (V), Current (A), Resistance (Ω), and Power (W), the remaining values are automatically calculated. It is widely used for electronics hobbies, electrical installation design, and checking the power consumption of household appliances.

For example, it is perfect for calculating the resistance value needed to limit the current of an LED, or for checking the wattage consumed by a USB device based on its current draw.

How to Remember the Formulas

・Voltage (V) = Current (I) × Resistance (R)
・Current (I) = Voltage (V) ÷ Resistance (R)
・Resistance (R) = Voltage (V) ÷ Current (I)

About Electric Power (Watts / W) Calculation

Electric power (P) represents the amount of electrical energy consumed per unit of time.
It is calculated using Power (W) = Voltage (V) × Current (I), and can also be expressed using Resistance (R) as W = I²R or W = V²/R.

Advantages of This Tool

Real-Time Calculation: Results are displayed the moment you type a number, making trial and error seamless.
Completely Free: All features are available for free without any hidden costs.
No Registration Required: Use it instantly without tedious account creation or logins.
Secure Design: Calculations run entirely inside your browser, meaning your input data is never sent to a server.

Frequently Asked Questions (FAQ)

Q. What happens if I enter three or more values?

A. Calculations are executed based on the values entered. Every time you change a field, the other items are automatically recalculated based on your priority lock rules.

Q. Can I enter decimal numbers?

A. Yes, it is fully supported. If you are calculating very small values (such as 100mA = 0.1A), please convert the units into standard Ampere (A) or Ohm (Ω) before inputting.

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