ENGINEERING
Ohm's law calculator
Calculate voltage, current or resistance from either of the other two values and inspect the corresponding ideal DC electrical power.
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No regional currency, unit or language profile is applied. This choice does not convert values or change formulas, results, routes or legal guidance.
Select the electrical quantity to calculate, then enter the other two values using volts, amperes and ohms.
Ohm's law result
- Voltage
- 20 V
- Current
- 2 A
- Resistance
- 10 Ω
- Electrical power
- 40 W
This ideal DC calculation applies only when the component behaves ohmically at the operating conditions. It is not electrical design, fault-current, component-rating or installation advice.
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Verification and calculation details
- Purpose
- Ohm's law calculator
- Variables and units
- Use the labelled fields and units shown in the calculator. Results use those units unless a conversion is stated.
- Formula and method
- The exact formula and worked example are shown below. Deterministic formula executed locally in the browser.
- Assumptions
- Only entered values and stated assumptions are included. Local fees, rules and professional requirements are excluded unless explicitly shown.
- Engine version
- 1.0.0
- Production verification baseline
- Release 63 · source
998803f - Verification run
release-v63-2026-09-20- Last verified
- — Automated release checks passing
Read the Calculation Standard · Report a calculation or source issue
How this calculator works
Ohm's law is V = I × R. Rearranging the same authority gives I = V ÷ R and R = V ÷ I. Ideal DC electrical power is P = V × I.
Variables and inputs
- Quantity to calculate
- Required numeric input. choose voltage, current or resistance.
- First known electrical value
- Required numeric input. finite value within the supported range; use the displayed SI unit.
- Second known electrical value
- Required numeric input. finite value within the supported range; resistance must be greater than zero when entered; current must be non-zero when solving resistance.
How to interpret the result
The calculator returns voltage in volts, current in amperes, resistance in ohms, ideal DC electrical power in watts. Read each output against the assumptions you entered, compare alternatives one variable at a time, and use the result as an estimate rather than a promise.
Common mistakes to avoid
- Mixing units or entering a rate as a decimal when the field requests a percentage.
- Rounding intermediate values instead of the final displayed result.
- Leaving out a cost, timing rule or local requirement listed in the assumptions below.
Practical uses
Use the ohm's law calculator to check a real scenario, compare a changed assumption and explain the arithmetic before relying on a quote, specification or decision.
Worked example
For 2 amperes through 10 ohms, voltage is 2 × 10 = 20 volts and ideal electrical power is 20 × 2 = 40 watts.
Assumptions and limitations
- the component behaves ohmically over the entered operating range
- resistance is constant for the calculation
- values describe the same ideal DC component and sign convention
- SI units shown beside each field are used consistently
- many devices are non-ohmic or change resistance with temperature and operating conditions
- does not model AC impedance, phase, component tolerances, transients or fault current
- does not verify wire, component, protection or installation ratings
- electrical work and safety decisions require applicable codes, manufacturer data and qualified review
Important notes
Results are estimates based on the values entered. Confirm rates, prices, units and professional requirements that apply in your location. Review the Answer Atlas Calculation Standard and corrections policy for formula, privacy and correction rules.
Frequently asked questions
What does Ohm's law calculate?
For an ohmic component, it relates voltage, current and resistance through V = I × R. Knowing two quantities lets the calculator solve the third.
Can I calculate electrical power too?
Yes. After solving the three Ohm's-law quantities, the calculator reports ideal DC power as voltage multiplied by current.
Does Ohm's law apply to every electrical device?
No. The proportional relationship applies only where the device behaves ohmically and resistance remains effectively constant at the operating conditions.