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Elliott Electric Supply

Calculating With Ohm's Law


This guide shows you the proper formula to use to calculate with Ohm's Law.

A. When Volts and OHMS are known:

Amperes = Volts
OHMS
or, I = E
R

Example: Find the current of a 120 volt circuit with a resistance of 60 OHMS.

I = E
R
= 120
60
= 2 Amperes


B. When Watts and Volts are known:

Amperes = Watts
Volts
or, I = P
E

Example:A 120 Volt Circuit has a 1440 Watt Load. Determine the current.

I = P
E
= 1440
120
= 12 Amperes


C. When OHMS and Watts are known:

Amperes = Square Root of Watts over Ohms

Example: A circuit consumes 625 watts through a 12.75 OHM resistor. Determine the current.

Example of the Amperes formula when Ohms and Watts are known

* One Electrical Horsepower = 746 watts. Electric Motors are rated in horsepower.
** One kilowatt = 1000 watts. Generators are rated in kilowatts.