Voltage, current, resistance and power are all linked. Enter any two and this calculator works out the other two using Ohm’s law and the power equation.
Quoting an electrical job? traqR turns your calcs into a priced quote, then a job, then an invoice — without re-keying a thing.
Start free trialVoltage equals current times resistance (V = I × R). Rearranged, it gives current (I = V ÷ R) or resistance (R = V ÷ I) whenever you know the other two.
Power equals voltage times current (P = V × I). Combined with Ohm’s law it also gives P = I²R and P = V²÷R.
Because the four quantities are linked, knowing any two lets you calculate the remaining two — which is exactly what this tool does.
Ohm’s law states that the current through a conductor is proportional to the voltage across it and inversely proportional to its resistance: V = I × R. It’s the foundation of nearly every electrical calculation, from sizing a resistor to understanding voltage drop.
Power (watts) equals voltage times current: P = V × I. If you know current and resistance instead, use P = I² × R; if you know voltage and resistance, use P = V² ÷ R. This tool applies whichever form fits the two values you enter.
These formulas apply directly to DC and to purely resistive AC loads. For AC circuits with inductance or capacitance, power factor comes into play and real power is P = V × I × power factor. For three-phase AC, use our three-phase calculator.
Ohm’s law underpins practical decisions — checking a load current, sizing components, understanding why a long run drops voltage, or diagnosing why a circuit draws more than expected. It turns guesswork into numbers.
This calculator is a general engineering aid, not a substitute for design to AS/NZS 3000 or professional judgement. Electrical work must be carried out and verified by a licensed electrician. Always confirm results against the relevant standards.
traqR turns your electrical work into professional quotes, jobs and invoices without re-keying. Try it free for 14 days.