Power draw is the amount of electrical energy a device consumes while it’s running, measured in watts (W). A 60-watt light bulb has a power draw of 60 watts; a gaming PC under heavy load might draw 500 watts or more. Understanding power draw helps you estimate electricity costs, choose the right power supply, and figure out how much your devices actually cost to run.
The Basic Formula
Power draw comes down to a simple relationship: power equals voltage multiplied by current (P = V × I). Voltage is the electrical pressure pushing energy through a circuit, and current is the flow of electricity itself. A device running on a 120-volt outlet and pulling 5 amps of current has a power draw of 600 watts.
For direct current (DC) circuits, like the ones inside your computer or phone charger, that formula is all you need. Alternating current (AC) circuits, which is what comes out of your wall outlets, add one wrinkle: something called the power factor, which accounts for how efficiently the device uses the electricity it receives. The real power consumed in an AC circuit is P = V × I × power factor. Most modern appliances have a power factor close to 1, so the simple formula still gets you in the ballpark.
Two other useful variations of the formula use resistance (measured in ohms): P = I²R, and P = V²/R. These let you calculate power draw when you know resistance but not voltage or current. You won’t need them for everyday use, but they’re the foundation of how engineers design electrical systems.
Power Draw of Common Appliances
Household devices span an enormous range. A TV draws 50 to 400 watts depending on screen size and technology, with OLED and plasma panels sitting at the higher end. Compact microwaves pull 600 to 900 watts while running, and full-size models reach 1,000 to 1,200 watts. Refrigerators are rated at 100 to 800 watts, but because the compressor cycles on and off throughout the day, their actual average draw is closer to 150 to 250 watts over time.
That cycling behavior matters. A device’s rated wattage tells you its peak draw, not necessarily what it uses minute to minute. An air conditioner rated at 1,500 watts doesn’t pull 1,500 watts continuously. It ramps up, reaches temperature, and cycles down. Your real energy consumption depends on how often and how long the device actually runs at full power.
Power Draw in PCs and Gaming Hardware
If you’re building or upgrading a computer, you’ll run into several overlapping terms for power draw. Thermal Design Power (TDP) describes how much heat a processor is designed to produce under sustained load, which roughly corresponds to its power consumption. For graphics cards, manufacturers use Total Board Power (TBP) or Total Graphics Power (TGP) to describe the entire card’s consumption, including fans, LED lighting, and microcontrollers on the board itself.
These numbers matter when choosing a power supply unit (PSU), but there’s a catch: your PSU draws more from the wall than it delivers to your components. A power supply operating at 80% efficiency that delivers 400 watts to your hardware actually pulls 500 watts from the outlet. The extra 100 watts becomes heat. Higher-efficiency PSUs waste less. A Bronze-certified unit running at 85% efficiency would draw about 470 watts from the wall to deliver that same 400 watts internally. Gold, Platinum, and Titanium certifications push efficiency progressively higher, saving energy and producing less heat inside your case.
Standby Power: The Hidden Draw
Devices that appear to be “off” often aren’t. Anything with a standby light, clock display, or remote control sensor continues drawing small amounts of power around the clock. This is sometimes called vampire power or phantom load. Your cable box, microwave clock, game console in sleep mode, and smart speakers all contribute. Individually, each device might only pull a few watts, but collectively, standby power can add up to 20 percent of your monthly electric bill.
Plugging these devices into a power strip you can switch off, or using smart plugs that cut power on a schedule, is the simplest way to eliminate standby draw.
How to Measure Power Draw
The easiest way to measure any device’s real power draw is with a plug-in watt meter. Products like the Kill A Watt meter plug into your outlet, and then you plug the device into the meter. It displays real-time wattage, voltage, amperage, and cumulative energy use in kilowatt-hours. These meters typically cost $20 to $40 and work with anything that uses a standard outlet.
For whole-home monitoring, devices like the Emporia Vue clamp onto your electrical panel and track energy use across every circuit in real time, showing you exactly which parts of your home consume the most power. This is especially useful if you have solar panels and want to understand your net energy production and consumption.
Turning Watts Into Dollars
Your electric company charges by the kilowatt-hour (kWh), which is one kilowatt (1,000 watts) used for one hour. Converting a device’s power draw into monthly cost takes three steps:
- Convert watts to kilowatts. Divide the device’s wattage by 1,000. A 200-watt device is 0.2 kW.
- Multiply by hours of use. If that device runs 8 hours a day for 30 days, that’s 240 hours. So 0.2 kW × 240 hours = 48 kWh per month.
- Multiply by your electricity rate. At the U.S. average of roughly $0.16 per kWh, that 200-watt device costs about $7.68 per month to run.
This calculation explains why high-wattage devices that run for long periods, like space heaters, window AC units, and electric dryers, dominate your electricity bill. A 1,500-watt space heater running 8 hours a day costs roughly $57 per month at the same rate. Meanwhile, a laptop pulling 50 watts for the same duration costs under $2.
Power draw also scales with efficiency. Two refrigerators of the same size can have meaningfully different power draws depending on age, insulation quality, and compressor technology. An older model might average 250 watts over time, while a newer Energy Star model averages 150 watts, saving you $30 or more per year on that single appliance.