# What’s A Watt? How To Calculate Your RV Power Needs

The following entry is a very basic explanation of watts to help new RVers understand the term and what it means to them when calculating power needs. Many more pages can and have been written on this subject, and I encourage RVers to take the time to understand the electrical needs of both 12-volt and 120-volt in their RV.

I recently wrote a post about using a back-up UPS as a convenient source of low wattage shore power when dry camping. From some of the comments I received to that post and comments I see online regarding 120-volt power needs when dry camping, there seems to be a mystery on what a watt is and how you can use this unit of energy measurement when calculating power consumption.

As an RVer, all you need to know about watts is that they are a unit of energy consumed/supplied over time. For example, a 100-watt light bulb will consume 100 watts of electrical energy in one hour. Power consumption – Photo via iRV2 Forums

It doesn’t matter if the power source is 12 volts or 120 volts, the consumption, as expressed in watts, remains the same. Most (though not all) 120-volt appliances list the watts (many times designated by a “W”) they consume either on the back of the appliance or in the owner’s manual.

One of the comments I received on my previous blog post is shown below. Answering both parts of this question is quite simple. If the reader looks up the power consumption of his satellite receiver and flatscreen, he will have everything he needs to figure out if the device will power the two items and for how long.

Let’s say the flatscreen draws 175 watts and the receiver draws 25 for a total of 200 watts. The UPS unit I blogged about is rated at 480 watts. The answer to the first question is “yes” as the power consumption is less than the power source (480 watts).

Now if you will remember, watts are the consumption of energy over time (one hour). To answer the second part of this question, you just take the available power 480 watts and divide by the load 200 watts which will give you a rough number of hours the power source will power the load, which is 2.4 hours.

Resistance, inefficiencies, and other variables may impact the results for the example given above and other applications, but it is a good rule of thumb for newbies. No need to fill the comment box pointing this out!

In my next article, I will explain how to determine watts when it is not listed on the appliance and how to convert watts to amp hours when calculating how long your house batteries will last under a given load. Doing the math, just another adventure in RVing! 