Ohm's Law Calculator
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 9/3/2026
Ohm's law gives the voltage of an electrical circuit with the formula U = R × I, where R is resistance in ohms and I is current in amps. For a resistance of 10 Ω carrying a current of 2 A, the voltage is 20 V.
Explanation
Ohm's law is one of the fundamental relationships in electricity: it links voltage (U, in volts), resistance (R, in ohms), and current (I, in amps) in a simple electrical circuit, via the formula U = R × I. This law applies directly only to so-called "ohmic" components (like a standard resistor), whose behavior stays proportional regardless of the applied voltage — this isn't true of every electronic component (a diode, for example, doesn't follow this linear relationship). From this same formula, you can also find the resistance (R = U ÷ I) or the current (I = U ÷ R) if you know the other two quantities; this calculator is set up for the most common use — finding the voltage from R and I. For the electrical power consumed by this same circuit, see our electrical power calculator.
Example: 10 Ω resistance, 2 A current
Inputs
Resistance: 10 Ω. Current: 2 A.
Calculation
Voltage = resistance × current = 10 × 2 = 20.
Result
The voltage across this circuit is 20 V.
Frequently asked questions
How do I find resistance or current using this same law?
By rearranging the formula: resistance = voltage ÷ current (R = U ÷ I), and current = voltage ÷ resistance (I = U ÷ R). This calculator is set up to find the voltage from the other two quantities, the most frequent use case.
Does this formula work for all electrical components?
No, only for so-called ohmic components (like a standard resistor), whose behavior stays linear regardless of voltage. Components like diodes, transistors, or filament bulbs don't follow this simple relationship across their whole operating range.
What's the difference between voltage, current, and resistance?
Voltage (in volts) measures the electrical potential difference, the force that pushes current along. Current (in amps) measures the actual flow rate of the current. Resistance (in ohms) measures the circuit's opposition to that current flowing — the higher it is, the more voltage is needed to push the same current through.