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Ohm's Law Calculator

Enter any two of voltage, current, resistance and power and get the other two, with all 12 formula variants shown and an animated circuit whose charge carriers move with the current.

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Coulomb's Law CalculatorSolve F = kq₁q₂/εᵣr² for the force, either charge or the distance, in any of 18 dielectric media, with charges in C, µC, nC or elementary charges, plus the potential energy and the field at q₂.Kepler's Third Law CalculatorGet the orbital period from T = 2π√(a³/GM) with the semi-major axis in AU, km or solar radii and the central mass in solar, Earth or Jupiter masses — plus orbital speed and the a³/T² constant.Snell's Law CalculatorSolve n₁sin θ₁ = n₂sin θ₂ for either angle or either index, get the critical angle, and watch the incident, reflected and refracted rays move on a live diagram — total internal reflection included.Beer-Lambert law calculatorSolve the Beer-Lambert law A = ε·c·l for any variable — absorbance, molar absorptivity, concentration or path length. Central to spectrophotometry, it links how much light a solution absorbs to how concentrated it is. Pick what to solve for, enter the rest, and read the answer.Spring constant calculator (Hooke's law)Hooke's law three ways: solve for the spring constant k = F/x, the restoring force F = k·x, or the displacement x = F/k. It handles single springs and N identical springs in series (k/N) or parallel (N·k), and adds the stored elastic energy ½kx².Hooke's law calculatorCompute the force of a spring from its stiffness and displacement (F = kx).Ideal gas law calculatorCompute the pressure of a gas from moles, temperature and volume (PV = nRT).Capacitor energy calculatorCompute the energy stored in a capacitor from its capacitance and voltage (E = ½CV²).

Ohm's Law Calculator works straight from this page — free, instant, nothing to install. You will find it under Electronics, with Coulomb's Law Calculator and Kepler's Third Law Calculator for the neighbouring cases.

How to use it

  1. Open the tool — no signup or install needed.
  2. Enter your input or adjust the available options.
  3. Get your result instantly, then copy or download it.

Frequently asked questions

What does Ohm's Law Calculator do?

Enter any two of voltage, current, resistance and power and get the other two, with all 12 formula variants shown and an animated circuit whose charge carriers move with the current.

When would I actually use this?

At the bench: sizing a resistor for an LED, reading a colour band, working out a divider ratio, and checking a part will not cook.

What is the most common mistake?

Choosing a resistance and forgetting the power rating. A value that is electrically right will still burn if the package cannot dissipate what passes through it — check the watts as well as the ohms.

How is Ohm's Law Calculator different from Coulomb's Law Calculator?

They sit next to each other but answer different questions. Coulomb's Law Calculator: solve F = kq₁q₂/εᵣr² for the force, either charge or the distance, in any of 18 dielectric media, with charges in C, µC, nC or elementary charges, plus the potential energy and the field at q₂. Pick whichever matches what you're starting from — both are free.

Is there a tool for the next step?

Kepler's Third Law Calculator is the closest one after this: Get the orbital period from T = 2π√(a³/GM) with the semi-major axis in AU, km or solar radii and the central mass in solar, Earth or Jupiter masses — plus orbital speed and the a³/T² constant.

Where do the figures come from?

Ohm's law and the divider formulas are exact. Colour bands follow the IEC standard; real components carry a tolerance, so a nominal value and a measured one will not match exactly.

Further reading

All guides →
ExplainerWhat Is Ohm's Law? V = I × R Explained SimplyOhm's law links voltage, current, and resistance with one equation: V = I × R. Learn the triangle trick and see worked examples.ExplainerResistors in Series and in Parallel: The Formulas, and the Three Things They Do Not Tell YouSeries adds, parallel adds reciprocals — that part is easy. The parts that catch people: which member dominates the answer, why two 5 % resistors in parallel are still 5 %, and why the smallest resistor in a parallel pair takes the largest share of the power.How-toHow to Calculate an LED Series ResistorSize the series resistor for any LED with one formula: R = (Vs − Vf) / I. Follow the steps, see a worked 5 V example, and pick the right resistor.ExplainerOne Time Constant Is 63 % of the Way, Not the End1,000 Ω with 100 µF gives a time constant of 0.1 s. The capacitor is 63 % charged at that point, 95 % after three constants and 99.3 % after five — the last of which is the number that matters.ExplainerA 5,000 mAh Power Bank Does Not Hold 5,000 mAh for Your Phone5,000 mAh drawn at 500 mA with 85 % efficiency runs for 8.5 hours instead of the arithmetic's 10. The same 15 % explains why a 5,000 mAh bank barely fills a 4,000 mAh phone once.ExplainerDouble the Current and the Cable Gets Four Times HotterPower lost as heat is current squared times resistance. Ten metres of 1.5 mm² extension lead has 0.233 Ω there and back: 23.3 W at 10 A, and 59.7 W at 16 A.