Complete guide
Electricity calculator for volts, amps, ohms and watts
Select any supported pair of voltage, current, resistance and power. Calculator24 solves the other two values and shows equivalent power formulas.
The four electrical quantities
Voltage is electric potential difference, current is charge flow, resistance opposes current and power is the rate of energy transfer.
Ohm's law and power
For an ohmic component, voltage equals current times resistance. Substitution produces two additional power identities.
V=I×RP=V×IP=I²RP=V²/RWorked 120-volt example
A 2-amp resistive load at 120 volts has 60 ohms of resistance and consumes 240 watts under the ideal model.
Selecting the known pair
Only the two quantities named by the selector are used. Other visible values remain available when you switch methods.
DC and simple resistive scope
Alternating-current circuits may require RMS quantities, impedance and power factor. Motors and electronic loads can also draw startup or nonlinear current.
Electrical safety
Calculator results do not select conductors, breakers or safe work practices. Follow applicable codes and qualified instructions before touching energized equipment.
SI electrical units
| Quantity | Symbol | Unit |
|---|---|---|
| Voltage | V | volt |
| Current | I | ampere |
| Resistance | R | ohm |
| Power | P | watt |
Frequently asked questions
What is Ohm's law?
V=IR for an ohmic component.
How do I calculate watts?
Multiply volts by amps for the supported ideal model.
Can I use this for AC motors?
It does not model power factor, impedance or inrush current.
Why must values be positive?
This tool reports magnitudes for a load rather than signed circuit direction.
Does it size a breaker?
No. Protection and conductor sizing require code-specific analysis.
What pair should I select?
Choose exactly the two quantities you know from measurement or specification.
What to keep in mind
This ideal DC or resistive-load calculation does not include AC phase, power factor, inrush current, conductor sizing, protection or code requirements. De-energize work and use qualified electrical guidance.
Results display up to 8 decimal places; exported numbers preserve calculation precision. This is a calculation summary, not an official certificate.