You can't really convert directly from watts to amps or amps to watts because the two units measure very different aspects of electrical current. With that said, the concepts of watts, amps and volts are all intrinsically related. So if you know any two of these measures, you can use that information to find the missing measure. This is helped along by the fact that in the United States, most outlets are standardized to 120V electrical current. If you assume that to be true and you know the wattage, you're just a few calculations away from finding amps.
TL;DR (Too Long; Didn't Read)
To convert from watts to amps at a fixed voltage, divide watts by volts.
The Water Analogy
To understand the key concepts of electricity denoted by watts, volts and amps, it's helpful to think of electricity as water flowing through a pipe. Amps represent the quantity or volume of water flowing through the pipe, and the voltage represents the amount of water pressure – just like the water pressure that comes out of your shower head or bathtub faucet. The overall power of the water running through the pipes would be measured by volume × pressure or, to bring it back to the realm of electricity, the power (watts) produced by the water are calculated by amps × volts.
That gives you a few key formulas you can use to become your own amp calculator, all assuming a fixed voltage:
Converting From Watts to Amps
Once you have at least two of the three pieces of information (amps, watts and volts), finding the missing element is as simple as choosing the right formula, plugging in the information you already have and then doing some basic math to find the missing piece. For example, if you know the watts and volts but want to know the amps, you'd select the amps equation.
Example 1: Imagine that you have a blender with a 600-watt motor on a fixed 120V household circuit. How many amps is it?
So the blender is rated for 5 amps. Note that appliance ratings often aren't that specific; for example, everything from blenders to electric skillets may have a turbo, peak or similarly "high-powered" mode that draws higher amperage than typical use. So you'll often see appliances rated with a certain fudge factor; for example, a blender might be rated for 5 to 6 amps instead of simply 5 amps.
Example 2: Imagine that you have an air conditioner rated for 1500 watts on a fixed 120V circuit. How many amps is it?
So the air conditioner is rated for 12.5 amps, although you'll often see this rounded to the next highest number.
Converting From Watts to Amps
In a similar vein, if you know the amps and volts of a household appliance, becoming your own watt calculator is as simple as choosing the right equation.
Example 3: Imagine that you want to know how many watts it takes a charge a laptop. If you know that the laptop is rated for 0.5 amp and a fixed household current of 120 volts, you choose the following equation and plug in the missing pieces:
So the laptop draws 60 watts of electricity as it charges.
- Voltage, wattage and amps can be confusing concepts. It is helpful to imagine electric current as water coming from a tap and into a washing machine. The water pressure is the voltage, amps are the gallons per minute that are flowing out of the tap and wattage is the actual number of gallons the washing machine used to do its job.
About the Author
Lisa studied mathematics at the University of Alaska, Anchorage, and spent several years tutoring high school and university students through scary -- but fun! -- math subjects like algebra and calculus.
Calculator image by Alhazm Salemi from Fotolia.com