Ohms Law Calculator
The triangle on your own numbers: V = IR with the whole power family derived live — three roads to one watt — and the short-circuit case refused by name.
Ohms Law Calculator
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- Ohmic, steady-temperature elements only
- DC straight-line case; no reactance or phase
In short: Push 2 A through 60 Ω: V = I·R = 2 × 60 = 120.000000 V. The power card derives the family from your two numbers three ways and watches them agree: P = V·I = 240 W, P = I²R = 240 W, P = V²/R = 240 W — three roads, one watt, which is the check that the arithmetic is one law. The car card moves the same resistor to a 12 V rail: only 0.200000 A flows — voltage sets the current through a fixed resistance. Ask for R = 0 and the page refuses: zero resistance is a short circuit, and the wiring answers, not the law.
Formula
V = I·R · P = V·I = I²R = V²/R · short: R = 0 refused
Ohm's law is the definitions page of electricity: voltage is the per-charge push, current the charge flow, resistance the opposition — and the three are bound by one multiplication. The power family falls out by substitution; the page derives all three forms from YOUR numbers so 'one watt' is something you watched happen rather than a remembered identity.
Worked Example
- Enter any two of current and resistance (this page's pair).
- Read the third — here the voltage — and the power family derived three ways.
- Use the 12 V card to see what a fixed resistance does when the supply changes.
- For the other pairings, the voltage, current and resistance pages each own their question.
Defaults: 120.000000 V; power 240 W by all three roads; on a 12 V rail the same element draws 0.200000 A.
Strengths & Limits Of This Model
Where this engine is strong
- Power family derived three ways from your inputs
- Short circuit refused and named
Where it stops
- No AC impedance or non-ohmic devices
- Fixed-temperature resistance assumed
Practical Use Cases
Electronics
bias points and dropping resistors
Household
what a load draws on your mains
Teaching
the power family, derived not asserted
Methodology & Editorial Standards
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Ohms Law Calculator — 8 Expert FAQs
8 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
Why does the page refuse R = 0?
Because zero resistance is not a load, it is a short circuit: the law's arithmetic would need zero volts for any current, and the real question — how much current does the SOURCE and its wiring survive — is not this equation's to answer. The page refuses and names the case rather than print a confident wrong number.
Which page should I use for my two knowns?
This page pairs current with resistance. If your knowns are power and current, the voltage page owns the question (V = P/I); power and voltage belong to the current page (I = P/V); and the resistance page prices resistance itself from wire geometry. Same triangle, different doors — each page asks its own question so the cards teach something, not mirror.
Why derive power three ways?
Because the three roads agreeing IS the law working: P = V·I becomes I²R by substitution and V²/R by the same move. When your two inputs make all three agree to the digit, you have checked the arithmetic without a calculator's opinion.
Does Ohm's law always hold?
It holds for ohmic materials — metals at steady temperature, carbon films, most wiring. A hot filament's resistance climbs, diodes refuse the straight line entirely, and semiconductors play by curve rules. The page prices the straight-line case and says so where the line bends.
Why does the open-circuit case print zero?
Zero current through the resistor means zero voltage ACROSS it — an honest zero, and a useful one: it is why an ammeter in series reads the load and a voltmeter across a dead branch reads nothing. Zero flow is a measurement, not a failure.
Is AC covered?
Not here. With alternating current, coils and capacitors add reactance, and the R in the triangle becomes impedance with phase attached. Resistive heaters on AC behave exactly as this page computes; motors and supplies do not.
Where does the heat come from at 240 W?
From the electrons' work pushing through the lattice — I²R heating, continuous while current flows. A soldering tip, a toaster, a fault in a wall: the same law, at very different consequences. The power card is also the safety card.
How does this pair with the resistance page?
That page computes R from geometry — material, length, wire gauge — before any current flows. Feed its number into this page's R field and you have chained the wire's physics to the circuit's behaviour: one run of copper, two pages.