Calculate voltage, current and resistance with Ohm's law
Find the missing quantity by entering the two you know. The calculation applies to an ohmic load and shows the working.
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Worked example
- Calculate: Voltage
- Resistance: 46 Ω
- Current: 5 A
Result
Voltage
230 V
Working
- U = R × I
46 Ω × 5 A = 230 V
The three quantities in Ohm's law
Ohm's law describes the relationship between voltage, current and resistance. Voltage is given in volts, current in amps and resistance in ohms, written Ω. The calculator can find each of the three quantities when the other two are known.
The relationship applies to an ohmic, also called resistive, load. It should therefore be used for a circuit or a component where this assumption fits. The calculator does not determine whether an installation, a cable or a fuse is suitable.
The formulas for voltage, current and resistance
The voltage is found with U = R × I. To find the current, I = U / R is used. To find the resistance, R = U / I is used. Choose the calculation you want before you fill in the known values.
When dividing, the denominator must not be zero. That applies to the resistance when the current is calculated, and to the current when the resistance is calculated.
Example with resistance and current
The resistance is 46 Ω and the current is 5 A. The voltage is 46 Ω × 5 A = 230 V. If the current is calculated back from these values, the working is 230 V / 46 Ω = 5 A.