Watts, Volts, and Amps, Oh My!


Scott Stankus, SITA Instructor

Today I want to take a moment to briefly discuss Watts, Volts, Amps and Ohms.  What they mean and how they correlate. 

As a homeowner, active real estate inspector or a real estate inspector student knowing how these relate and what they tell us is important. As a homeowner, it can help you identify why a breaker keeps tripping.  As an inspector, understanding these fundamental electrical concepts will help you evaluate systems and guide your clients.

Many times, a system of water pipes is used as an example to help people understand how the units of electricity work together. Using this example, voltage is equivalent to water pressure, amps is equivalent to flow rate, and Ohms are equivalent to pipe size.  All of this flows in a pipe or hose.

Continuing with our example above, imagine a tank of water attached to a hose (conductor in electrical terms). If we increase the pressure (voltage in electrical terms) in the tank, more water will come out of the hose (amps in electrical terms).

If we reduce the diameter of the hose, resistance (Ohms in electrical terms) is increased.  Increased resistance results in reduced current.

Let’s put each of these into our example above:

Volts (V)

This is the base unit to determine voltage.  Using our analogy, a battery or electric station is like a water pump that propels water through a pipe. The pump increases the pressure in the pipe, causing the water to flow.  In electrical terms, the pressure in the pipe is voltage (measured in volts).

As with water, as the pump works more, the more water flows.  In electrical terms, as the voltage increases, so does the current (amps); but for the current to flow, it must flow through the wire (conductor) back to the source.  If there is an interruption, say with a switch, the flow will stop.

Amps (A)

Amps, short for amperes, tell us how much current is flowing.  It is the base unit for electricity in the International System of Units.  In our plumbing example, this would be how much water is flowing through the pipe. 

Ohms (Ω) 

Tells us resistance to flow.  In our plumbing example, it would be the size of the pipe.  In electrical systems, it would be where the flow of electricity experiences resistance – like at a light fixture. 

Watts (W)

Tell us power – how much energy is released (or used) per second in a system.  You may see appliances reference how many watts they use.  Space heaters, hair driers, microwaves, etc. may state 1250, 1500 or 1800 watts to express how much energy is consumed by those appliances.

Continued below

Putting it together in a Power Triangle:

Using the triangle below can help you easily convert from one measurement to another when you know two of the values.  In the example below (a simplified version of Watt’s law); W is Watts, A is Amps and V is Voltage.

In the hairdryer example, we can calculate how many amps a 1500-watt hairdryer would use.  We know that the hairdryer runs on 120 volts and uses 1500 watts.  1500 watts divided by 120 volts is 12.5 amps.

Now let’s say we needed to know how many watts a particular amperage breaker would be able to handle on a 240-volt circuit.  Using the triangle to the right, we multiply the amps by the voltage to get the total number of watts available for consumption.  Let’s say we have a 60-amp breaker on a 240-volt circuit.  We multiply 60 by 240 and get 14,400 watts. 


I hope this article has helped you understand how the different ways we measure electricity correlate and how you can get the value of one of the measurements when you know the other two values.

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