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Ohms Law Calculator

Enter any two known values and select the pair you are providing. The calculator will compute the remaining values using Ohm's Law and power relations.

Tip: Choose the correct units for each value. If you change your mind, simply adjust the inputs and resubmit.

Note: Provide positive, non-zero values for the selected known pair to avoid invalid divisions. The calculator assumes ideal DC conditions.

Use this Ohms Law Calculator to quickly solve for voltage (V), current (I), resistance (R), and power (P). Enter any two known values and the tool computes the remaining quantities instantly, complete with unit support and adjustable precision.

What is Ohm’s Law?

Ohm’s Law is the foundational relationship that links voltage, current, and resistance in electrical circuits. In its simplest form, it states that the voltage across a component is equal to the current through it multiplied by its resistance: V = I × R. When you also consider power, you can derive additional relationships, such as P = V × I, P = I2R, and P = V2/R. These equations allow you to move effortlessly between electrical quantities as long as you know any two of them.

How to use the Ohms Law Calculator

  1. Select which two values you will provide (for example, Voltage and Current).
  2. Enter the numerical values and choose the appropriate units (V, mV, kV; A, mA; ?, k?, M?; W, mW, kW).
  3. Optionally set the number of decimal places for the results.
  4. Click Calculate to compute the remaining values instantly.

For the most reliable results, use positive, non-zero values for the selected known pair. The tool assumes ideal direct current (DC) conditions without reactive components such as inductors or capacitors.

Formulas used by the calculator

  • Ohm’s Law: V = I × R
  • Power (from V and I): P = V × I
  • Power (from V and R): P = V2/R
  • Power (from I and R): P = I2R
  • Derived: I = V/R, R = V/I, V = ?(PR), I = ?(P/R)

Why this calculator is helpful

This Ohms Law Calculator streamlines everyday electronics tasks, from verifying resistor selections to estimating safe power levels. By supporting common unit prefixes, it reduces manual conversions and errors. The adjustable precision lets you match the level of detail needed for lab work, prototyping, or quick field checks.

Practical examples

  • Given V = 12 V and I = 0.5 A: R = 24 ? and P = 6 W.
  • Given V = 5 V and R = 1 k?: I = 5 mA and P = 25 mW.
  • Given I = 2 A and R = 4 ?: V = 8 V and P = 16 W.

Common mistakes to avoid

  • Mixing units (for example, using mA while calculating as though they were A). Always check unit prefixes.
  • Using zero for values that appear in the denominator, which leads to undefined results.
  • Applying DC formulas to AC circuits with significant reactance; this tool is for ideal DC or resistive AC cases.

Understanding units and prefixes

Electronics commonly uses metric prefixes to represent very large or very small values. This calculator accepts and converts between mV, V, kV; mA, A; ?, k?, M?; and mW, W, kW. A quick refresher: milli (m) is 10?3, kilo (k) is 103, and mega (M) is 106. Choosing the right prefix keeps numbers readable and reduces errors when interpreting results.

When to use the Ohms Law Calculator

Whether you are sizing resistors for an LED, checking the load on a regulator, or estimating heat dissipation in a power resistor, this tool gives fast, reliable answers. For education, it helps students visualize how changing one variable affects the others. For professionals, it speeds up design checks and documentation.

Next steps

Try different pairs of known values and observe how the outputs change. If your application involves AC circuits with significant reactance, consider using specialized impedance calculators to account for inductance and capacitance.

FAQs

How do I use the Ohms Law Calculator to find resistance?

Select Voltage & Current as your known pair, enter both values, and the Ohms Law Calculator will compute resistance and power.

Can the Ohms Law Calculator solve for power from voltage and resistance?

Yes. Choose Voltage & Resistance, enter your values, and the calculator outputs current and power instantly.

What units does the Ohms Law Calculator support?

It supports mV, V, kV; mA, A; ohms, k?, M?; and mW, W, kW, with automatic conversion to SI for accurate results.

Does the Ohms Law Calculator handle zero or negative values?

No. For stability, it requires positive, non-zero inputs for the selected known pair to avoid undefined results.

Can I use the Ohms Law Calculator for AC circuits?

Use it for purely resistive AC cases. For reactive circuits with inductance or capacitance, use an impedance-based tool.

How precise are the results from the Ohms Law Calculator?

You can set decimal places from 0 to 10. The calculator rounds outputs to your chosen precision.

Will the Ohms Law Calculator show all four values after I submit?

Yes. After you provide any two values, it computes and displays voltage, current, resistance, and power.

Why does the Ohms Law Calculator ask me to choose a known pair?

Selecting a known pair ensures the calculator applies the correct formulas and avoids ambiguous inputs.