Ohms Law Calculator

When you know two electrical values, the third often isn’t something you need to work out by hand.

This Ohms Law Calculator lets you calculate voltage, current, or resistance from the values you already have. It can also calculate electrical power, giving you a more complete picture of what is happening in the circuit.

Enter the values you know, select the appropriate units, and let the calculator handle the rearranging of the formula.

⚡ ELECTRICAL CALCULATOR

Ohm's Law Calculator

Calculate voltage, current, resistance, or electrical power from the values you already know. Choose the quantity you want to find and enter the other two values.

What do you want to calculate?

I Current

V Voltage

R Resistance

Voltage

Current

Resistance

Please enter valid values greater than zero in the required fields.

Your result

Calculated Current

—

Enter values to calculate

I = V ÷ R

Power: —

Note: This calculator uses the standard Ohm's law relationships for voltage, current, resistance, and power. For circuits containing reactive or nonlinear components, additional electrical analysis may be required.

Ohm's Law Formula Reference

V = I × R Find voltage

I = V ÷ R Find current

R = V ÷ I Find resistance

P = V × I Find power

What Is Ohms Law?

Ohms law describes the relationship between voltage, current, and resistance in an electrical circuit.

Its most familiar form is:

V = I × R

Where:

V = voltage in volts
I = current in amperes
R = resistance in ohms

The same relationship can be rearranged depending on what you are trying to find:

I = V ÷ R

R = V ÷ I

That simple relationship is why knowing any two of the three quantities allows you to calculate the missing one.

The Four Values Behind the Calculation

Although Ohms law itself deals with voltage, current, and resistance, electrical power is closely connected through:

P = V × I

This gives four useful quantities to work with:

Quantity	Symbol	Unit	What it represents
Voltage	V	Volt (V)	Electrical potential difference
Current	I	Ampere (A)	Rate of electric charge flow
Resistance	R	Ohm (Ω)	Opposition to current
Power	P	Watt (W)	Rate of electrical energy transfer

Power can also be expressed using resistance:

P = I² × R

and

P = V² ÷ R

These relationships are useful when you want to go beyond simply finding the missing value and estimate how much power a resistive load is consuming.

Which Ohms Law Formula Should You Use?

The easiest way to choose a formula is to look at the quantity you don’t know.

Finding voltage

If current and resistance are known:

V = I × R

Example:

2 A × 8 Ω = 16 V

Finding current

If voltage and resistance are known:

I = V ÷ R

Example:

24 V ÷ 12 Ω = 2 A

Finding resistance

If voltage and current are known:

R = V ÷ I

Example:

9 V ÷ 0.5 A = 18 Ω

Finding electrical power

If voltage and current are known:

P = V × I

Example:

12 V × 2 A = 24 W

These are algebraic rearrangements of the same basic electrical relationships rather than separate calculation methods.