Voltage calculator
Voltage is current times resistance (V = IR), power divided by current (V = P/I), or the square root of power times resistance (V = √(PR)). Half an amp through 24 ohms means 12 volts and 6 watts dissipated.
How to find voltage
Ohm’s law and the power relationship together give twelve rearrangements of four quantities, which is why the "Ohm’s law wheel" exists as a poster on workshop walls. Knowing any two gives the other two. The practical point is that voltage is almost never the thing you measure indirectly — a meter gives it to you directly — so this page mostly earns its place in design work: choosing a supply for a known load, or working out what a divider or dropper resistor will present downstream.
Questions
V = I × R from Ohm’s law. Combined with P = V × I you also get V = P ÷ I and V = √(P × R).