How to Calculate Watts Using Voltage and Amperage
You don’t have to be an electronics or engineering wiz-kid to understand the fundamentals of electrical systems. Hearing about volts, amps, and watts can be confusing if you’re not familiar with what each term means. But learning about the basics isn’t as daunting as you’d think. In fact, when we break it down, it’s pretty straightforward. Understanding watts, amps, and voltage is crucial for ensuring your appliances work properly and, most importantly, safely.
In this guide, we’ll explain how to calculate watts using voltage and amperage, so you can be confident in powering your home appliances.
Understanding Watts, Amps, and Volts
Before we jump into calculations, it’s good to understand the basics:
Amperes or amps: This measures how much electricity is flowing through a circuit. To think of it in simple terms, imagine water flowing through a pipe. Amps are the rate of the water flowing through the pipe.
Volts: Volts are the electrical pressure that pushes the current through the wire. Think of volts as the water pressure in a pipe. The higher the voltage, the stronger the electrons are being pushed through.
Watts: Watts represent the power a device uses. They tell you how much energy is being produced or consumed over time.
Each of these elements makes up the building blocks of how electricity works. Watts measure energy, amps quantify the current, and volts drive the current. Knowing how it functions will help you better understand your appliances and home backup power solutions.
The Core Formula: Watts = Amps × Volts
The basic formula for calculating watts is as follows:
Watts = amps x volts
This simple equation shows you how electrical power is calculated. Let’s break it down with an example to better understand how it works:
Let’s suppose you have a device that draws 12A at 100V, the wattage will be:
Watts: 12A X 100V = 1200W
Or, say you have a phone charger that draws 5A at 5V, the wattage will be:
Watts: 5A X 5V = 25W
How Amps and Volts Shape Current Flow
If we return to the water pipe example from earlier, we can think of volts as the pressure pushing the water through the pipes. Amps, on the other hand, measure how much of that water is actually flowing at any given time. The higher the voltage, the stronger the force of water, and the higher the amps, the more charge is flowing through.
Together, volts and amps determine the wattage of your devices. Knowing this means you correctly match your devices and appliances to the right power sources and avoid potentially overloading circuits. It’s also essential for sizing wiring and ensuring efficient energy use in your home.
AC vs. DC: Key Differences in Power Use
Now that we’ve grasped the basics, it’s time to get the down-low on AC vs. DC power systems. These are the two main types of electrical current, and while both deliver energy, they work in different ways.
Alternating Current (AC) output: Like the name suggests, the AC current constantly changes the direction it’s flowing in, instead of travelling in a steady path. It’s more commonly used in large-scale transmission and in the supply of power to homes and businesses. It’s also regularly used for power grid supply.
Direct Current (DC) output: The direct current moves in a single, constant direction. It’s most commonly used for electronic devices and renewable systems that need a constant, stable supply of power.
The calculation formula watts = amp x volts is still relevant, but AC systems can be influenced by something called the “power factor”, especially in devices that have inductive or capacitive loads, such as fridges, washing machines or air con units.
In simple terms, this means that not all of the electricity that flows in AC units turns into actual usable power. Some might get lost along the way, and because of this, the power you measure is a little bit less than what the formula suggests. This is why we consider the power factor when calculating AC systems to get a more accurate reading.

Estimating Wattage to Size a Power Station
To estimate the power you’ll want for your power station, there are a few things you’ll need to consider. Before you begin, think about all of the devices you’ll need to power with your power station. Then, check the manual or device label to find the voltage and amps of each item. Following the calculation formula, multiply the volts by the amps to get the wattage, e.g., 5V x 4A = 20W.
Add up all of the totals from all of the devices you want to run to find the total power needed. Once you have the total, it’s time for the fun part! You can start browsing for power stations and find one that will work for you. You should look for a system that has at least 20% more wattage capacity than you’ve estimated you’ll need. This leaves some extra wiggle room to make sure you have a stable supply and won’t overload the power station.
A portable power station like the EcoFlow DELTA 3 Max Plus has 1800W continuous AC output and up to 3600W with the X-Boost surge mode. That’s enough to handle everything from your everyday essential gadgets to your heavy-duty appliances. The best part? You can get up to 10 years of reliable power thanks to their EV-grade LiFPO4 batteries.
DELTA 3 Max Plus Portable Power Station
Frequently Asked Questions
Why Is It Important To Calculate Watts?
Calculating watts is extremely important for ensuring that you choose the right cables, outlets and power stations so your devices operate safely and efficiently. Whether you need to calculate the power for your home appliance or you’re calculating for devices on a larger scale, understanding the basic calculation formula is crucial.
Can I Use the Same Formula for Both AC and DC Power?
Yes, the watts = amps × volts formula applies to both AC and DC power. For DC, the calculation is straightforward. For AC, you must also account for the power factor, which reflects efficiency losses. Ignoring it may lead to inaccurate results when estimating real power usage.
What Happens if My Device Lists Only Watts but Not Amps or Volts?
If your device only lists watts, you should assume that the voltage is standard for its particular power source, such as 12V for a car or 5V for USB. Then, you can reverse the formula by calculating as amps = watts ÷ volts.

Calculating Watts Improves Efficiency and Builds Energy Confidence
Understanding watts, volts, and amps isn’t rocket science; in fact, it’s actually pretty simple once it’s broken down into a basic formula. Getting familiar with the fundamentals of electricity means not only can you boast about it to those who don’t know, but you can also confidently and safely run your home appliances without a hitch.
Whether you’re powering small devices like your phone charger, or choosing a portable power station like the EcoFlow DELTA 3 Max Plus, calculating wattage gives you peace of mind that you can keep you and your devices powered and safe from any electrical mishaps.