Ohm’s Law Calculator
Solve voltage, current, or resistance, with wattage included for quick electrical sanity checks.
Enter values
Use the example values or enter your own equipment/spec scenario.
Results update locally in your browser.
Engineering sanity check
Scenario rows and safety notes for planning—not final design approval.
Educational estimate only. Verify electrical, safety, code, and equipment requirements with qualified sources.
What this means
At 10 A through 12 Ω, voltage is 120 V and estimated power draw is 1,200 W.
| Formula triangle | Use when | Formula |
|---|---|---|
| V over I × R | Voltage unknown | V = I × R |
| I = V ÷ R | Current unknown | I = V / R |
| R = V ÷ I | Resistance unknown | R = V / I |
| P = V × I | Power/heat estimate | P = V × I = I²R = V²/R |
| Scenario | Current | Voltage | Power | Resistance |
|---|---|---|---|---|
| 50% current | 5 A | 60 V | 300 W | 12 Ω |
| Base current | 10 A | 120 V | 1,200 W | 12 Ω |
| 150% current | 15 A | 180 V | 2,700 W | 12 Ω |
- Current
- 5 A
- Voltage
- 60 V
- Power
- 300 W
- Resistance
- 12 Ω
- Current
- 10 A
- Voltage
- 120 V
- Power
- 1,200 W
- Resistance
- 12 Ω
- Current
- 15 A
- Voltage
- 180 V
- Power
- 2,700 W
- Resistance
- 12 Ω
Copy / print
Copy or print this local-only worksheet for your own notes, spec checks, or supplier questions.
Watch-outs
- Electrical safety, heat, wire sizing, fuse/breaker sizing, and code requirements are outside this simple calculation.
- Real components can vary with temperature, tolerance, waveform, and load conditions.
- Use qualified sources for mains voltage, batteries, vehicles, and safety-critical circuits.
Formula
Voltage = current × resistance. Power = voltage × current.
Notes
This calculator is an educational estimate. Verify safety, code, equipment, and manufacturer requirements with qualified sources before using results in real systems.
Use the Ohm’s Law Voltage Calculator without guessing what to do next
- Start with the example values to see what the main result looks like.
- Replace the example values with the best numbers you have right now; rough estimates are fine for a first pass.
- Change one input at a time so you can see which assumption actually moves the answer.
What the result means
The result is a quick technical check based on a standard formula or unit relationship. It helps you sanity-check a spec before deeper review.
How to use it
Use it to catch order-of-magnitude problems: a value that is wildly too high, too low, or in the wrong unit before it reaches a drawing, quote, or part list.
What can change it
Do not treat a simple calculator as engineering approval. Real equipment decisions can depend on tolerance, safety factor, code, heat, duty cycle, and manufacturer limits.
Good for
Calculate voltage from amps and ohms.
Check this next
Try Power Converter, Energy Converter, Pressure Converter to cross-check the same decision from another angle.
Best habit
Run a conservative case and an optimistic case. The gap between them is often more useful than a single answer.
Common uses
- Calculate voltage from amps and ohms.
- Estimate wattage from current and resistance.
- Sanity-check simple electrical scenarios.
Common questions
Is the Ohm’s Law Voltage Calculator private?
CalcShelf calculators run without an account. Your entries stay in the calculator while you work; CalcShelf does not save them or place your numbers in shareable links.
How accurate is the Ohm’s Law Voltage Calculator?
It is a formula check, not stamped engineering. Tolerance, safety factor, heat, duty cycle, environment, and manufacturer limits can change real equipment choices.
What should I check after using the Ohm’s Law Voltage Calculator?
Verify units, specs, tolerances, safety factors, code requirements, and manufacturer data before choosing parts or equipment.
Which calculator should I try next?
Try Power Converter, Energy Converter, Pressure Converter as next checks so you can compare the same decision from another angle before acting.
Method behind the estimate
Engineering tools use standard unit relationships and simple mechanical, electrical, pressure, energy, density, or flow conversions.
Why the detail matters
For design, safety, warranty, or production work, verify against official specifications, standards, tolerances, and qualified engineering review.
No account or saved inputs
Your calculator values are for your session. CalcShelf does not require an account, save calculator entries, or add your numbers to shareable URLs.
Copy or print safely
Use any copy, print, or worksheet controls as local handoff tools for your own notes, supplier calls, lender questions, or implementation checklist. They are there to help you explain the result to a human.
Before acting
Treat the result as a decision draft, not a verdict. Recheck the source numbers, run a downside case, and verify the real-world rule, quote, label, or spec that controls the final answer.
Last reviewed: May 11, 2026. See methodology and editorial policy for formulas, assumptions, rounding, review approach, and limitations. For production, code, safety, or equipment changes, verify against official specs.