Georg Ohm did his work on resistance in the years 1825 and 1826, and published his results in 1827 as the book Die galvanische Kette, mathematisch bearbeitet, meaning The Galvanic Circuit Investigated Mathematically. His hard work that was influenced by many others is available to you in a simple calculator.
Voltage (V) = Current (I) * Resistance (R)
Power (P) = Voltage (V) * Current (I)