Electrical
Electrical Ohm's Law Calculator
Explore the available resistive-circuit equations and check whether the input pair supports the quantity you want to solve.
Result
Ohm's law describes a resistive DC circuit. AC circuits with motors, transformers or electronics have reactance as well as resistance, so current and voltage fall out of step and the simple product overstates real power.
Get a Free Business AuditWhat moves the number
- Solve for selects the equation rather than treating all visible fields as simultaneous measurements.
- Power, voltage and resistance must refer to one operating condition.
- Input units matter when converting milliamps or kilohms to the units shown.
Where this one goes wrong
Entering a complete but inconsistent set of values does not make this a circuit solver. It selects a relationship and derives results from that relationship. Keep a record of the chosen mode when comparing scenarios or discussing a discrepancy.
Questions
About this calculator
Will it combine several resistors?
No series or parallel network is described by the form. Determine the relevant equivalent resistance separately before using a single-resistance equation.
Can this infer an insulation fault?
No. A numerical relationship does not identify fault location or establish insulation integrity. Diagnostic measurements require their own methods and interpretation.
Why is calculated power different from an AC meter?
A resistive equation omits reactive behavior. Use an appropriate AC assessment, and treat any subsequent code-governed circuit sizing as a separate planning task.
The formula
V = I x R; P = V x I; and the rearrangements of both
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How to use this calculator
- Solve for. Choose the unknown quantity. Only the inputs used by that calculation are shown.
- Current (A). Enter your own figure; the page starts at 2.
- Resistance (ohms). Enter your own figure; the page starts at 60.
The result updates as you type, so you can try a figure, see what it does to voltage, and change it back. Nothing you enter is sent anywhere or saved.
A worked example
These are the figures the calculator opens with. Every number in the results column below is produced by the same calculation the page runs, so you can follow it through before putting your own figures in.
What goes in
| Input | Value |
|---|---|
| Solve for | Voltage |
| Current (A) | 2 |
| Resistance (ohms) | 60 |
What comes out
| Result | Value |
|---|---|
| Voltage main result | 120.0 |
| Current | 2.0 |
| Resistance | 60.0 |
| Power | 240.0 |
At 120.0 V and 2.0 A, the circuit dissipates 240.0 W through 60.0 ohms.
How sensitive the answer is
Holding everything else steady and changing only current (a), this is what happens to voltage. It is worth knowing which of your inputs the answer actually hinges on, and which barely move it.
| Current (A) | Voltage |
|---|---|
| 1 | 60.0 |
| 1.5 | 90.0 |
| 2 example above | 120.0 |
| 3 | 180.0 |
| 4 | 240.0 |
Every other input is held at the example value while this one changes, which is not how a real job behaves. Treat it as a guide to which number matters most, not as five separate quotes.
What each figure means
- Solve for
- Choose the unknown quantity. Only the inputs used by that calculation are shown.
- Current (A)
- A number, between 0 and 10000, starting at 2.
- Resistance (ohms)
- A number, between 0 and 1000000, starting at 60.
What the results tell you
| Result | What it is |
|---|---|
| Voltage | Potential difference derived from the selected input pair, shown in volts. |
| Current | Current consistent with the selected resistive-circuit equation, shown in amperes. |
| Resistance | Resistance consistent with voltage and current. A zero-current open circuit has no finite derived resistance. |
| Power | Electrical power calculated as voltage times current. This is watts, not energy in kilowatt-hours. |
Before you rely on this number
Conductor sizing, voltage drop and load figures are governed by code, and the code takes precedence over any calculator. Ambient temperature, conduit fill, continuous load factors and the specific installation all change the answer. Treat this as a first pass, not a design.
Keep going
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