What Is Ohm’s Law?
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What Is Ohm’s Law?
What is Ohm’s law? It is the formula that links voltage, current and resistance in an electrical circuit. Fluke describes it as “a formula used to calculate the relationship between voltage, current and resistance in an electrical circuit.” This page gives the formula, its rearrangements, and a worked example. It is a short reference, not a full circuit analysis guide.
Quick answer
- Voltage (E) = current (I) × resistance (R).
- In words: volts = amps × ohms.
- Rearranged for resistance: R = E / I (ohms = volts / amps).
- Rearranged for current: I = E / R, the same relationship solved for current.
The three quantities
Voltage is measured in volts, current in amperes (amps), and resistance in ohms (Ω). Fluke’s resistance page says the voltage across a circuit “is equal to the current (I) flowing through it times the resistance (R).” Current is written as I “for intensity” in formulas such as Ohm’s Law.
Worked example
This example is arithmetic, not a measurement from any source. Suppose a circuit has 12 V across a 4 Ω resistance. Then I = E / R = 12 / 4 = 3 A. If the resistance rises to 6 Ω with the same 12 V, the current falls to 2 A, which matches Fluke’s point that higher resistance means lower current flow.
Why technicians use it
Fluke notes that resistance cannot be measured in an operating circuit. Troubleshooting technicians therefore often determine resistance by taking voltage and current measurements and applying Ohm’s Law.
Safety
Measuring voltage and current in a live circuit carries shock risk. Work on mains wiring can kill. Panel and service work belongs to a licensed electrician.
How we chose
This explainer covers only the terms that the sources we opened define in their own text. We opened the pages listed under Sources on 2026-10-27 and used only passages on those pages. We left out related topics the sources do not cover, such as AC circuit analysis and component values.
What we could not verify
The sources we opened give the formula and its rearrangements, but not a set of worked circuits from a manufacturer. The worked example above is our own arithmetic. The sources we opened do not cover AC circuits with reactive components, which this article does not address.
FAQ
What is the formula?
Fluke’s resistance page gives it as volts = amps × ohms, so voltage (E) equals current (I) times resistance (R).
How do I find resistance from voltage and current?
Rearranged, R = E / I, or ohms = volts / amps, according to Fluke.
Who was Ohm?
Fluke says Georg Simon Ohm (1784-1854) was a German physicist who studied the relationship between voltage, current and resistance.
Is Ohm’s law used to find resistance in a live circuit?
Fluke notes that resistance cannot be measured in an operating circuit, so technicians often take voltage and current measurements and apply Ohm’s Law instead.
Sources
- Fluke Learn, “Ohm’s Law” fluke.com/en-us/learn/blog/electrical/ohms-law (opened 2026-10-27)
- Fluke Learn, “What is Resistance?” fluke.com/en-us/learn/blog/electrical/what-is-resistance (opened 2026-10-27)
- Fluke Learn, “What is Current?” fluke.com/en-us/learn/blog/electrical/what-is-current (opened 2026-10-27)
