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Ohms Law Calculator
Solve for volts, amps, ohms or watts from any two.
Fill in any two. Leave the other two blank and they will be calculated.
How each value was found
Every rearrangement
| To find | From V and I | From V and R | From I and R |
|---|---|---|---|
| Voltage (V) | — | — | V = I × R |
| Current (A) | — | I = V / R | — |
| Resistance (Ω) | R = V / I | — | — |
| Power (W) | P = V × I | P = V² / R | P = I² × R |
Useful conversions
| Quantity | Value |
|---|
Results
Voltage—
Current—
Resistance—
Power—
Derived
Energy per hour—
Conductance—
Charge per second—
—
Minimum resistor power rating to use
Applies to DC circuits and purely resistive AC loads using RMS values. Circuits with inductance or capacitance need impedance in place of resistance and a power factor in the power calculation. Real wiring work belongs to a qualified electrician.
Quick Tool Overview
The Ohms Law Calculator takes any two of voltage, current, resistance and power and returns the other two, printing the formula it used for each. All twelve standard rearrangements are listed, which is the classic wheel diagram in table form.
- What it does
- Solves for volts, amps, ohms or watts from any two
- You give it
- Any two of V, I, R and P
- You get back
- The other two, with the formula used
- Best for
- Electronics projects, electrical study and quick checks
About the Ohms Law Calculator
Enter any two of voltage, current, resistance and power, and the remaining two are calculated. Every one of the twelve standard rearrangements is available, and the tool prints which formula it used for each result.
Ohm's law itself is the relationship V = I × R, and the power equation P = V × I is what turns it into the four-quantity wheel most electricians learn from. Combining them gives the less obvious forms — P = I²R and P = V²/R — which are the ones that explain why a small increase in current heats a conductor so much more than the same increase in voltage does. This applies to DC circuits and to purely resistive AC loads; reactive AC circuits need impedance and a power factor instead.
Key features of the Ohms Law Calculator
Any two inputs
Every valid pairing is handled, not just the classic V, I and R triangle.
Formulas shown
Each result names the rearrangement used, so the working can be checked rather than trusted.
Unit prefixes accepted
Milli through mega, so 4.7 kΩ and 4700 Ω both work without hand conversion.
The full relationship table
All twelve rearrangements listed, which is what the wheel diagram encodes.
AC caveat stated
The page notes that reactive AC circuits need impedance and a power factor instead.
How to use the Ohms Law Calculator
-
1
Enter any two values
Voltage, current, resistance or power. Leave the other two blank.
-
2
Read the remaining two
Calculated immediately, with the formula used shown for each.
-
3
Check the units
Prefixes from milli to mega are handled, so 4.7 kΩ and 4700 Ω are both accepted.
-
4
Use the relationship table
All twelve rearrangements are listed, which is the wheel diagram in table form.
Frequently asked questions
Voltage equals current multiplied by resistance: V = I × R. Rearranged, I = V / R and R = V / I. It describes how these three quantities relate in a resistive circuit.
P = V × I is the base form. Substituting Ohm's law gives P = I²R and P = V²/R, which are useful when you do not have both voltage and current directly.
Because power dissipated in a resistance goes as the square of current, P = I²R. Doubling the current quadruples the heating, while the resistance stays the same.
For purely resistive AC loads, yes, using RMS values. Circuits with inductance or capacitance need impedance in place of resistance and a power factor in the power calculation.
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