Energy
Estimate the energy needed to keep selected appliances running during an outage.
Enter your numbers to see the answer.
Essential loads calculator guide
Before you can size a battery, inverter, or generator you need one number: how much energy the appliances you refuse to lose will use over an outage. This calculator adds four common essential loads — refrigerator, lights, router and devices, and fans — as average watts, then multiplies the total by the number of backup hours to give kilowatt-hours. It is the first step whether you are planning an IPS for evening load-shedding in Dhaka or Lahore, a hybrid solar inverter for a home in Nairobi or Lagos, or a whole-house battery for storm outages in Texas or Queensland. Use average wattages, not nameplates: a refrigerator whose compressor is rated at 150 W typically averages 40 to 80 W over a day because it cycles on and off, whereas a ceiling fan on high draws a steady 60 to 80 W. Feed the resulting kWh into the battery-size calculator and the total watts into the inverter-size calculator to complete the design.
Average essential load (W) = refrigerator + lights + router and devices + fans. Essential energy (kWh) = average load ÷ 1,000 × backup hours.
Worked example with the default inputs: refrigerator 150 W, lights 100 W, router and devices 30 W, fans 100 W, for 8 backup hours. Total load = 150 + 100 + 30 + 100 = 380 W. Energy = 380 ÷ 1,000 × 8 = 3.04 kWh, which the calculator rounds to one decimal and displays as 3 kWh. The side rows show the 380 W average load, the 8-hour duration, and the 150 W refrigerator share, the largest single item in this list.
Each appliance field takes average power in watts. If you only have a kilowatt figure, multiply by 1,000; if you have amps at 230 V, multiply by 230 (or by 120 in North America). Lights should be the total of every fixture you will actually keep on — six 9 W LED bulbs are 54 W. Backup hours can be fractional, so a typical 2.5-hour evening load-shedding block is 2.5. The output is in kilowatt-hours; multiply by 1,000 for watt-hours when reading a small battery’s Wh label.
This is a modelled estimate, not a meter reading. Real consumption moves with weather, occupancy, appliance age, standing charges, and tariff structure, and equipment rarely runs at its nameplate rating. Use the figure to compare options against each other, then confirm against your own bill and the manufacturer's specification before committing to a purchase. On this page the figure rests entirely on refrigerator, lights, router and devices, fans, backup hours, market / jurisdiction, effective date, data source, update owner and review date, so start there if the essential loads calculator returns something you did not expect.
Good to know: the refrigerator is the load people most often get wrong in both directions — using its 150 W nameplate as a constant overstates energy, but forgetting that its compressor needs three to five times that for a second at start-up understates the inverter size. Adding a microwave, kettle, iron, or water pump “just for a few minutes” can double the required inverter rating even though it adds little energy. And a 1 ton air conditioner at 1,000 to 1,200 W would alone triple this default list; treat AC as a separate, deliberate decision.
Energy results depend on tariffs, equipment behavior, region, weather, and installation assumptions. Verify rates and electrical decisions with the utility, manufacturer, or qualified professional.
Sources
How it works
Estimate the energy needed to keep selected appliances running during an outage. This tool explains the calculation so you can adjust the assumptions to match your situation.
Worked example
With Refrigerator = 150 W · Lights = 100 W · Router and devices = 30 W · Fans = 100 W · Backup hours = 8 hours → 3 kWh (estimated essential-load energy). Change an input above and this example updates with your numbers.
Common questions
Start with a refrigerator or freezer, LED lights, the internet router and phone chargers, and fans in hot climates. Add a medical device, a small TV, or a water pump if needed. Leave electric heaters, kettles, irons, and air conditioners off unless the system is sized for them.
A minimal set — fridge 150 W, lights 100 W, router 30 W, fans 100 W — totals 380 W, or about 3 kWh over 8 hours. Add a small TV and laptop and you are near 4.5 kWh; add a 1 ton AC and it exceeds 11 kWh.
A modern 250 to 350 litre refrigerator averages 40 to 80 W over a day but draws 100 to 200 W while its compressor runs and 500 to 1,000 W for a moment at start-up. Use the average for energy and the start-up surge when choosing an inverter.
A 48-inch ceiling fan on high uses 60 to 80 W (0.06 to 0.08 kWh per hour); a pedestal fan 40 to 60 W; a BLDC ceiling fan 25 to 35 W. Four fans for an 8-hour night is roughly 2 to 2.5 kWh, often the largest load in a load-shedding backup plan.
Two fans (150 W), four LED lights (40 W), and a router (15 W) total about 205 W. For a 4-hour load-shedding block that is 0.8 kWh, roughly one 12 V 150 Ah lead-acid battery at 50% depth of discharge, and a 400 to 600 VA inverter with headroom.