Ohm's Law Calculator (V = I × R)

Ohm's Law states that the electric current flowing through a conductor is directly proportional to the voltage across it and inversely proportional to its resistance. The formula is U = I × R (or V = I × R), where U is voltage in volts, I is current in amperes and R is resistance in ohms.

Use the formula U = I × R. Select "Voltage" mode, then enter the known current (A) and resistance (Ω). Example: a current of 0.5 A through a 100 Ω resistor produces U = 0.5 × 100 = 50 V.

Use the formula I = U / R. Select "Current" mode and enter voltage (V) and resistance (Ω). Example: a 230 V supply across a 46 Ω load gives I = 230 / 46 ≈ 5 A.

Use the formula R = U / I. Select "Resistance" mode and enter voltage (V) and current (A). Example: 12 V across a component drawing 2 A gives R = 12 / 2 = 6 Ω.

Electric power P (in watts, W) is the rate at which electrical energy is transferred. The three equivalent formulas are P = U × I, P = I² × R and P = U² / R. The calculator automatically shows power alongside the main result.

A short circuit occurs when two points in a circuit are connected with near-zero resistance. From Ohm's Law, I = U / R — if R ≈ 0, the current becomes extremely large. This causes rapid heating of conductors, melted insulation, fire and equipment damage. Fuses and circuit breakers interrupt the circuit when current exceeds a safe limit.

In a series circuit, total resistance is the sum of individual resistances: R_total = R1 + R2 + ... + Rn. The same current flows through every element, and the voltage divides proportionally to each resistance. This is used, for example, to create a voltage divider.

In a parallel circuit, conductances add: 1/R_total = 1/R1 + 1/R2 + ... The voltage across each branch is the same, but current divides inversely proportional to resistance. Total resistance is always less than the smallest individual resistor.

No. Ohm's Law holds for ohmic conductors (e.g. metals at constant temperature) where resistance is independent of voltage. Non-ohmic devices — diodes, transistors, incandescent bulbs — have a resistance that changes with operating conditions. The calculator assumes an ideal ohmic resistor.

Select which quantity you want to find (voltage, current or resistance), then enter the two known values in their respective fields. The calculator instantly displays the computed result and the electric power. All values are rounded to four significant figures.