Ohm's Law Converter

Solve volts, amps, ohms, and watts from any two knowns in seconds, free and instantly offline with no signup required ever. Fill exactly two fields for the other two solved plus fuse-at-125 guidance LED resistor math and DC-only boundaries with fault explanations for builds vehicles panels homework and bench workflows.

Solve volt, amp, ohm, and watt relationships with this Ohm's Law Converter for electronics, circuit design, and voltage, current and resistance checks.

About Ohm's Law

Solve volts, amps, ohms, and watts from any two knowns in seconds, free and instantly offline with no signup required ever. Fill exactly two fields for the other two solved plus fuse-at-125 guidance LED resistor math and DC-only boundaries with fault explanations for builds vehicles panels homework and bench workflows.

How Ohm solving works in seconds: Fill exactly two of volts, amps, ohms, watts — blank the unknowns — to solve the other two via V=IR and P=VI rearranged twelve ways. A 12V 2A load resolves to 6Ω and 24W instantly. Results appear at $0 cost in your browser.

Why two-knowns matter for USA makers on 09/22/2026: Guessing resistor values smokes $50 LED builds and melts breadboards. Austin makers compute (12−2)/0.02 = 500Ω before touching soldering irons. Chicago RVers checking 12V fridges divide watts by volts to see if batteries survive the night.

Fuse sizing rule: Current equals power over volts — size fuses at 125 percent of continuous draw so a 1500W 120V heater pulls 12.5A on a 15A circuit legally. Miami homeowners sizing $500 panels avoid nuisance trips and fire risks with one division. New York landlords auditing buildings catch 20A breakers guarding 12-gauge wire correctly.

LED resistor math: Subtract LED forward voltage from supply, divide by target current — (12−2)/0.02 gives 500Ω at 0.2W dissipation. Denver students finishing homework verify wattage ratings so resistors run cool, not glowing. Seattle techs verifying $2,000 bench supplies confirm current limits before connecting prototypes.

DC limits and faults: Ideal resistive DC only — AC needs impedance and phase math this tool skips. Zero-ohm knowns imply infinite current, reported as no-solution since real circuits fault first. Temperature drift and reactive loads need dedicated calculators.

Privacy and local math: All solving runs entirely in your browser with no circuit values transmitted, logged, or stored. Design proprietary hardware and client panels privately at any hour.

E-bike builds: Boston shops wiring $3,000 conversions verify controller current against battery BMS limits before first throttle. Phoenix off-gridders sizing $25,000 solar arrays divide inverter watts by 48V to spec cable gauges on 09/22/2026.

Farm pumps: Dallas farms pumping $12,000 wells compute locked-rotor current to size starters that survive August heat. Atlanta studios lighting $2,000 sets balance dimmer loads so breakers hold through finales.

Food-truck power: San Francisco trucks running $800 inverters confirm fryer plus fridge draw stays under alternator output. Philadelphia elevator techs servicing $40,000 controllers verify coil draws before ordering $600 replacements.

Where it is used

Austin makers size $50 LED builds, Chicago RVers check 12V draw, Miami homeowners size fuses, Denver students finish homework, Seattle techs verify $2,000 supplies, and New York landlords audit $500 panels. Twelve rearrangements cover every pair Boston e-bike shops wire $3,000 builds, San Francisco food trucks run $800 inverters, Dallas farms pump $12,000 wells, Atlanta studios light $2,000 sets, Phoenix off-gridders size $25,000 arrays, and Philadelphia elevators service $40,000 controllers.

How to use the Ohm's Law

  1. Voltage V (leave blank if unknown) — enter the value (e.g. 12).
  2. Current A (leave blank if unknown) — enter the value (e.g. 2).
  3. Resistance Ω (leave blank if unknown) — enter the value.
  4. Power W (leave blank if unknown) — enter the value.
  5. Calculate — press the Calculate button to see the result instantly above.

Formula

V=IR P=VI 12 forms: V=IR/P/I/sqrt(PR); I=V/R/P/V/sqrt(P/R); R=V/I/V²/P/P/I²; P=VI/V²/R/I²R.

Examples

12V load

voltage:12
current:2
resistance:
power:
Result: R 6Ω P 24W

Heater element

voltage:120
power:1500
current:
resistance:
Result: 12.5A 9.6Ω USA heater

LED resistor

voltage:10
current:0.02
resistance:
power:
Result: 500Ω 0.2W

Frequently Asked Questions

Why exactly two fields?
Two independent equations (V=IR, P=VI) determine two unknowns. One leaves infinite solutions; three may contradict.
AC circuits?
Only purely resistive DC-equivalent cases. AC needs impedance and phase — use an AC power calculator.
Why NaN sometimes?
Zero knowns imply infinite results, like current through 0 ohms. Real circuits would fault first.
Is my data stored?
No. All solving runs locally in your browser. No values are transmitted, logged, or stored.
LED without resistor?
Never on voltage above forward drop — current runs away and kills the LED in seconds. Always compute the resistor.
Fuse at exactly load current?
No — size 125 percent above continuous draw so normal operation never trips while faults still clear fast.
Power ConverterForce ConverterAngle ConverterArchive ConverterArea ConverterBraille Converter