Ohm's Law Calculator

Solve Ohm's law — enter any two of voltage, current and resistance to find the third, plus power. Free, instant, no signup.

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A
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Formula: V = I × R • P = V × I
  • V = voltage (volts)
  • I = current (amps)
  • R = resistance (ohms)
  • P = power (watts)

How to use the Ohm's Law Calculator

  1. Enter your values. Fill in the fields with your numbers.
  2. Calculate. Press Calculate to run the ohm's law calculator.
  3. Use the result. Copy the result or try a related tool next.

Why use our Ohm's Law Calculator

Instant results. Enter your figures and the ohm's law calculator returns an answer in seconds.
Free & private. Runs in your browser — no signup, and nothing is sent to a server.
Accurate. Uses standard formulas so you can rely on the numbers.

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About the Ohm's Law Calculator

The Ohm's Law Calculator solves the relationship between voltage (V, in volts), current (I, in amps), resistance (R, in ohms) and power (P, in watts) in a DC resistive circuit. Ohm's Law itself states V = I x R, while Watt's Law adds P = V x I. Combining the two gives a set of twelve derived formulas, so once you supply any two of the four quantities the tool can solve for the remaining two. Enter two known values, leave the rest blank, and it computes the unknowns instantly without any algebra on your part.

Reach for this calculator whenever you are sizing or troubleshooting a simple electrical circuit. Common moments include choosing a current-limiting resistor for an LED, checking that a resistor's wattage rating won't be exceeded, working out the current a 12 V appliance will draw, or verifying a meter reading against expected values. Students use it to check physics and electronics homework; hobbyists use it on Arduino, 3D-printer and audio projects; and electricians use it for quick voltage-drop and load sanity checks. Because every result is mutually consistent, it doubles as a fast way to catch a mis-wired or mis-measured circuit.

Under the hood the tool picks the correct formula from your two inputs. If you give voltage and resistance it uses I = V / R; with current and resistance it uses V = I x R; with voltage and current it returns R = V / I and P = V x I. Power-based cases use the algebraic rearrangements, such as P = I squared x R, P = V squared / R, R = V squared / P and I = square root of (P / R). Keep your inputs in base units (volts, amps, ohms, watts) so milliamps become 0.05 A and kilo-ohms become 1000, and the outputs will be in the same base units.

Results are only as accurate as the assumptions behind Ohm's Law: it holds for linear, ohmic components like resistors and is intended for steady DC. For AC circuits with capacitors or inductors you must substitute impedance (Z) for resistance and use RMS values, and non-ohmic parts such as diodes and transistors won't follow a single straight-line ratio. Treat the wattage figure as a minimum and choose a component rated well above it. The calculation runs entirely in your browser using plain arithmetic, so the numbers you type are never uploaded or stored on a server.

Frequently asked questions

How many values do I need to enter?

Exactly two of the four quantities, voltage, current, resistance or power. From any valid pair the calculator derives the other two using Ohm's Law and Watt's Law.

What are the core formulas it uses?

The two roots are V = I x R (Ohm's Law) and P = V x I (Watt's Law). Everything else, such as I = V / R, R = V / I, P = I squared x R and R = V squared / P, is derived from those two.

Does Ohm's Law work for AC circuits?

Only with adjustments. For AC you replace resistance with impedance (Z), which accounts for capacitors and inductors, and use RMS voltage and current. This calculator assumes a simple DC resistive circuit.

How do I calculate the resistor wattage I need?

The power result (in watts) is the heat the resistor must dissipate. Pick a resistor rated comfortably above that figure, commonly at least double, so it doesn't overheat or fail.

Why are my numbers off by a factor of 1000?

Almost always a unit mismatch. Convert before entering: milliamps to amps (divide by 1000), kilo-ohms to ohms (multiply by 1000), and milliwatts to watts. The tool treats all inputs as base units.

From our blog

How to Evaluate a Pay Raise: From Percentage to Real Take-Home

By the Super Simple Digital Tools Team · Updated June 2026

When a raise lands in your inbox it usually arrives as a single number, either a percentage or a new salary figure, and that lone number hides a lot. The first move is to translate it into the same units you actually spend money in. A 3% bump on $65,000 sounds modest, but it's $1,950 a year, about $162 a month, and roughly $0.94 more an hour. Seeing all four views at once is the difference between a vague 'okay' and a real decision, and it's exactly what a pay raise calculator is built to surface in a single step.

The second step is benchmarking. A raise only means something relative to two things: inflation and the market. With cost-of-living adjustments running around 2 to 3 percent and the 2026 Social Security COLA set at 2.8%, a raise below that range is effectively a pay cut in buying power. Average employer salary budgets for 2026 sit near 3.5%, so anything meaningfully under that may signal you're being undervalued. Use the calculator to express your raise as a clean percentage, then hold it up against these reference points before you celebrate or negotiate.

Third, separate gross from net. The headline number on your offer letter is pre-tax, and a raise can quietly push part of your income into a higher marginal bracket. Only the dollars above the threshold are taxed at the higher rate, so a raise never reduces your overall take-home, but it does mean you keep less of each new dollar than of your base pay. Federal income tax plus Social Security and Medicare alone trim 7.65% off the top before income tax even applies, so plan around the net figure, not the gross.

Fourth, think in compounding terms for anything long-running. Raises stack on top of each other, so the base you start from matters more than any single year's percentage. Two years of 4% beats one year of 5% followed by a flat year, because the second 4% is calculated on an already-higher number. If you're weighing a job change, calculate the new annual figure and project a couple of years forward; a higher starting salary often outruns a slightly bigger one-time percentage at your current employer.

Finally, use the numbers to negotiate concretely. Walking into a review saying 'I'd like more' is weak; saying 'a 6% increase would bring me to $68,900, which aligns with market data for this role' is specific and hard to dismiss. Run the figures first so you can name an exact target salary, an exact percentage, and what it means per paycheck. The calculator removes the mental math, leaving you free to focus on the case you're making rather than the arithmetic behind it.

  • Enter both your current and proposed salary to get the exact raise percentage, then compare it directly against the 2.8% COLA and the ~3.5% average employer budget for 2026.
  • Always read the per-paycheck number, not just the annual one. A $1,800 raise feels large until you see it's about $69 per biweekly check before tax.
  • Estimate your net by keeping roughly 65 to 80 percent of the gross raise, since FICA alone takes 7.65% before income tax is applied.
  • When comparing a salaried offer to an hourly one, divide annual pay by 2,080 to get a true apples-to-apples hourly rate before deciding.

Read the full guide →

Tool by the Super Simple Digital Tools Team. Reviewed by our editorial team. Free to use, no signup required.

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