Quick Answers
Here are some quick answers to common questions about calculating wattage needs:
– Add up the wattage of all devices/appliances you plan to use at the same time. This gives you the total wattage needed.
– Check the wattage labels or manuals for each device to find the wattage usage.
– For lighting, assume 60W per standard bulb unless labeled otherwise.
– Major appliances like stoves, AC units, heaters have high wattage demands – check their specs.
– Device power usage is measured in watts (light bulbs, phones) or kilowatts (appliances, machinery). 1000 watts = 1 kilowatt.
– Consider intermittent surges – appliances with motors or compressors, like refrigerators and A/C units, require extra wattage on start-up.
Determining the Wattage of Common Household Devices
When calculating electrical load and wattage requirements for residential or commercial buildings, it is important to have an accurate understanding of how much power common devices and appliances utilize. Here is a brief overview of typical wattage for household electronics, lighting, HVAC systems, and large appliances.
Electronics
- Laptop computer – between 15 to 100 watts, depending on size and whether charging
- Desktop computer with monitor – 150 to 250 watts depending on components
- LCD/LED flat screen TV – 100 to 400 watts depending on size
- Game console – 70 to 200 watts depending on use
- Stereo receiver – 300 to 700 watts
- Tablet – 5 to 20 watts
- Smartphone – 3 to 6 watts charging
- CFL bulb – 5 to 25 watts
- LED bulb – 4 to 12 watts
Lighting
- Incandescent bulb – 40 to 100 watts
- CFL bulb – 5 to 25 watts
- LED bulb – 4 to 12 watts
- Halogen bulb – 25 to 100 watts
Heating and Cooling (HVAC)
- Window AC unit – 500 to 1500 watts
- Portable space heater – 600 to 1500 watts
- Whole house air conditioner – 3000 to 5000 watts
- Furnace blower motor – 800 to 1200 watts
Major Appliances
- Refrigerator – 500 to 800 watts
- Clothes washer – 350 to 500 watts
- Clothes dryer – 1800 to 5000 watts
- Dishwasher – 1200 to 2400 watts
- Microwave oven – 700 to 1100 watts
- Electric oven – 2000 to 5000 watts
- Electric stove top – 1000 to 3000 watts per burner
When in doubt, check the wattage plate or manual for appliances to determine their actual power draw. Understanding the approximate electric power consumption of household devices is key to calculating an accurate total wattage load.
Calculating Total Wattage Needed
To determine the total wattage you will need, follow these steps:
- Make a list of all electrical devices and appliances you need to run at the same time.
- Lookup the rated wattage of each device and record it.
- Add up the wattage values of all devices on your list.
- The total is the minimum wattage capacity needed.
As an example, let’s imagine we need to run the following items simultaneously in a living room:
| Device | Wattage |
|---|---|
| 3 LED bulbs | 12 watts each = 36 watts |
| Television | 200 watts |
| Desktop computer & monitor | 200 watts |
| Stereo | 500 watts |
Totaling the wattage values of the individual devices:
36 watts (lights) + 200 watts (TV) + 200 watts (computer) + 500 watts (stereo) = 936 watts
Therefore, to run these items simultaneously we would need a power supply of at least 936 watts.
Accounting for Safety Margins
When determining your total wattage requirement, it is recommended to add an extra buffer beyond the calculated total. This accounts for a few factors that can increase your power usage:
- Temporary surges – Some appliances with motors or compressors, such as refrigerators and air conditioners, require short bursts of extra wattage on start up before settling into normal operation.
- Voltage drop – The longer the wiring run between your devices and the main electrical panel, the greater the voltage drop. Lower voltage means more amperage is pulled to deliver the same wattage.
- Extra capacity – It’s always better to have slightly more capacity than you need to allow for future expansion or additions down the road.
To account for these factors, it is recommended to add an extra 20-25% “safety buffer” to your calculated wattage total.
Using the previous example, where we calculated a total of 936 watts, with a 25% buffer we would plan for:
936 watts x 1.25 = 1170 watts
Wattage Estimates For Common Rooms and Spaces
Here are some general wattage guidelines for frequently used rooms and living spaces:
Living Room
With TV, stereo, and 3-5 lamps lit expect 1000-1500 watts.
Kitchen
Major appliances, lighting, gadgets – plan for 2000-3000 watts.
Bedroom
Lighting, TV, computer – estimate 500-1000 watts.
Bathroom
Lights, hairdryer, fan – up to 1000 watts.
Home Office
Desktop computer, lighting, chargers – around 500 watts.
Garage
Electric garage door, various tools – allow 1500-2000 watts.
These wattage estimates assume typical devices and appliances for each space. The actual amount can vary considerably based on the number and types of electronics, tools, lighting, and equipment plugged in.
Special Considerations for High Power Devices
Some home appliances and equipment require very high wattage. If your residence has any of the following, be sure to account for their electrical demands:
- Electric vehicle charger – can draw 3000+ watts depending on charge rate
- Hot tub or spa – heaters and pumps use 3000-6000 watts
- Well water pump – 1000-3000 watts, depending on pump size
- Swimming pool – pumps and filtration systems up to 5000 watts
- Heat pumps – larger units need 3000-5000 watts
- Air conditioning – central AC over 3000 watts
Check nameplate ratings to get accurate wattage requirements for larger appliances and equipment. Their high power demand can significantly impact your overall electrical service needs.
Sizing Your Electrical Service
Once you’ve calculated your expected peak wattage demand, you can determine if your existing electrical service is sufficient, or if an upgrade is needed. Compare your total estimated wattage to the capacity of your electrical panel.
100, 150, 200 Amp Panels
For a 100 amp panel, plan on a continuous load up to 80% of capacity – around 8000 watts.
For a 150 amp panel, continuous load up to 12,000 watts.
And for a 200 amp service, 16,000 watts continuous power available.
If your estimated wattage exceeds 80% of your main panel rating, you may need a larger electrical service.
Wattage Capacity By Wire Gauge
| Wire Gauge | 50 ft. Run Capacity | 100 ft. Run Capacity |
|---|---|---|
| #12 AWG | 24 amps / 3000 watts | 20 amps / 2400 watts |
| #10 AWG | 30 amps / 3600 watts | 25 amps / 3000 watts |
| #8 AWG | 40 amps / 4800 watts | 35 amps / 4200 watts |
| #6 AWG | 55 amps / 6600 watts | 45 amps / 5400 watts |
| #4 AWG | 70 amps / 8400 watts | 60 amps / 7200 watts |
| #2 AWG | 95 amps / 11,400 watts | 80 amps / 9600 watts |
When running long distance wiring from your main panel to an outlet, voltage drop becomes a concern. Larger gauge wire is needed to deliver the same wattage over longer cable runs. These values give the approximate capacity by wire size.
Tips for Reducing Electrical Load
If your current electrical service is already near capacity, there are ways to reduce your power usage and avoid costly upgrades:
- Switch older appliances to newer ENERGY STAR models
- Replace incandescent bulbs with LED lighting
- Install timers or motion sensors on outdoor lighting
- Use power strips to completely shut off standby electronics
- Wash clothes in cold water, air dry dishes to reduce appliance loads
- Seal air leaks around doors and windows to improve HVAC efficiency
- Ensure equipment and wiring is up to code to maximize efficiency
With smart usage habits and electrical conservation, you can potentially cut your wattage demand significantly.
Conclusion
Determining your electrical service needs requires carefully tallying the wattage of all devices run simultaneously, leaving margin for surges and future expansion. If your total estimated load approaches your main panel’s capacity, an upgrade may be required. Or you can reduce your usage by employing more efficient devices and conservation habits. Properly sizing your home or building’s electrical service according to calculated wattage requirements ensures adequate power for safe, reliable operation.
