Electrical
Voltage Calculator
Calculate voltage from power and current, or from current and resistance.
Result
Electrical work is life-safety work governed by the NEC or your local code, and must be designed and installed by a licensed electrician. Conductor and overcurrent sizing depends on ambient temperature, conductor bundling, termination ratings, continuous-load rules and more. This is an educational estimate and must never be used as the basis for an installation.
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About this calculator
What are standard voltages?
In North America, 120 V and 240 V for residential, with 208 V, 277 V and 480 V common in commercial three-phase systems. Much of the rest of the world uses 230 V single phase.
Why does my measured voltage differ from nominal?
Supply voltage varies within a tolerance band, and voltage drop across long runs reduces it further under load. A reading a few per cent below nominal is normal.
The formula
V = P ÷ I, or V = I × R
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