How the home load calculation works
The home load calculator adds up your appliances in three steps. First, it multiplies each appliance's watts by its quantity to give your connected load, the power your home would draw with everything on at once. Second, it multiplies watts by quantity and by hours of daily use to give your energy, the units (kWh) your home burns in a day and in a month. Third, it reads your backup selection and your daily units against fixed size bands and names a UPS, generator and solar size that fits.
The two numbers answer different questions. Connected load decides how big your inverter or generator must be, since equipment fails on watts, not on units. Daily units decide your bill and your solar size, since a solar system must replace energy over a day, not power at an instant. A home can have a modest connected load and a heavy daily bill, or the reverse, and the calculator keeps the two figures separate for that reason.
Every preset watt figure in the tool is editable. Presets describe a typical appliance from the Pakistan market, and your own unit's nameplate sticker outranks any preset on this page.
Appliance watt table
The table below lists the preset values the calculator starts from, with the units each appliance burns in a typical day at common hours of use.
| Appliance | Typical watts | Units per hour | Typical hours | Units per day |
|---|---|---|---|---|
| LED bulb | 9 | 0.009 | 6 | 0.05 |
| Ceiling fan (old) | 80 | 0.08 | 12 | 0.96 |
| Ceiling fan (inverter, BLDC) | 35 | 0.035 | 12 | 0.42 |
| Refrigerator (medium) | 150 | 0.15 | 10 | 1.50 |
| LED TV 43 in | 100 | 0.10 | 5 | 0.50 |
| Air conditioner 1 ton inverter | 1,000 | 1.00 | 8 | 8.00 |
| Air conditioner 1.5 ton inverter | 1,500 | 1.50 | 8 | 12.00 |
| Iron | 1,000 | 1.00 | 1 | 1.00 |
| Washing machine | 500 | 0.50 | 1 | 0.50 |
| Water motor 1 HP | 750 | 0.75 | 1 | 0.75 |
| Microwave oven | 1,200 | 1.20 | 0.5 | 0.60 |
| Electric kettle | 1,500 | 1.50 | 0.5 | 0.75 |
| Wi-Fi router | 10 | 0.01 | 24 | 0.24 |
| Electric geyser | 2,000 | 2.00 | 2 | 4.00 |
One pattern in the chart surprises most readers. A single inverter air conditioner at eight hours a day burns more units than the fans, lights, fridge and television of the whole house combined. Any plan to cut a bill, or to size a solar system, starts with the air conditioner hours and works down from there.
How the size bands are decided
The table below states the exact band logic the calculator uses, so you can check any result by hand.
| Output | Formula | Bands the result rounds up to |
|---|---|---|
| UPS or inverter size | Backup watts divided by 0.8 power factor | 700, 1000, 1400, 2000, 3000, 4000, 5500 VA |
| Generator size | Total connected watts times 1.3 surge margin, divided by 1000 | 1, 2.5, 3.5, 5, 7.5, 10, 15, 20 kVA |
| Solar system size | Daily units divided by 4.2 units per kW per day | 1, 2, 3, 5, 6, 8, 10, 12, 15, 20 kW |
Each formula carries one planning judgement, and the page states all three openly. The 0.8 divisor converts watts into the volt-ampere rating that inverters carry on their boxes. The 1.3 generator margin covers motor starting surges from fridges, freezers and pumps. The 4.2 figure is a conservative planning average for the daily units one kilowatt of rooftop panels produces in Pakistan after losses; a shaded roof produces less, and a clean, well-angled roof can produce more.
The backup column deserves one more line. Only the appliances you mark for backup enter the UPS formula. Air conditioners and geysers usually stay off the backup line, which is why a home with 4,682 connected watts can sit behind a 1000 VA inverter at night without a single trip.
Worked examples
A small flat with everything on backup
Four LED bulbs at 9 W run six hours, two ceiling fans at 80 W run ten hours, a 150 W refrigerator runs eight hours, and a 100 W television runs five hours. The connected load is 36 plus 160 plus 150 plus 100, which is 446 W. The daily energy is 216 plus 1,600 plus 1,200 plus 500 watt-hours, which is 3.52 units a day and 105.5 units a month. The UPS band is 700 VA, the generator band is 1 kVA, and the solar band is 1 kW.
A 5 marla family home
A 1.5 ton inverter AC at 1,500 W runs eight hours, a 1 ton unit at 1,100 W runs six hours, a 200 W refrigerator runs ten hours, four 80 W fans run twelve hours, eight LED bulbs run six hours, and a washing machine, a 750 W water motor and two 120 W televisions fill the rest of the day. The connected load comes to 4,682 W, or 4.68 kW. Daily energy totals 27.32 units, and the month lands near 819.7 units. The backup selection of fans, lights and televisions draws only 632 W, so the UPS band is 1000 VA, while the generator band is 7.5 kVA and the solar band is 8 kW.
A student room
A 75 W fan runs eight hours, three LED bulbs run seven hours, a 65 W laptop runs six hours, and a 10 W router never sleeps. The connected load is just 177 W, and the day uses 1.42 units, about 42.6 units a month. Even a small room rounds up to the 700 VA UPS band and the 1 kVA generator band, since equipment sizes start there.
Summer load through the season
The candles below track the family home from the worked examples across the hot months. Each candle shows a low day, the average day and a high day in units.
The candles stretch in June and July and narrow again in September, and appliance count explains almost none of that movement. The same house, with the same devices, burns 24 units on an April day and 37 units on a July peak day because the air conditioners run longer and start against hotter rooms. Solar sizing that uses a winter month as its base underbuilds the system for the two months that matter most.
Common mistakes when sizing backup and solar
Asking the shopkeeper a question with no numbers in it. "Which UPS runs two fans and four lights" invites a guess. A written load list turns the same visit into arithmetic, and arithmetic does not trip at night.
Forgetting the refrigerator's starting surge. A fridge draws a multiple of its running watts for a few seconds at each start. Two appliances starting together can trip an inverter that handles either one alone.
Sizing solar from the bill total instead of daily units. Bills mix fixed charges, taxes and slab effects into one number. Daily units describe your actual energy, and the meter gives them to you for free with two readings a day apart.
Trusting preset watts over the nameplate. Presets are starting points. The sticker on your own motor, fridge or AC states its real rating, and the tool lets you type that figure over any preset.
Why I built this calculator
I bought my first UPS for the family home in Multan the way most people buy one. I walked into the shop and asked which unit runs two fans and four lights. The shopkeeper sold me a 1000 VA inverter, and the inverter tripped on the first night, because the refrigerator had quietly joined the backup line and nobody had added its starting surge to anything.
The next evening I sat down with the inverter manual, a notebook and a phone torch, and I read the nameplate sticker on every appliance in the house. Fan by fan, light by light, the notebook filled with the load list that this calculator is built on. The corrected purchase, made after measuring instead of before, never tripped again. With time I also stopped blaming the shopkeeper for that first night. He had not been dishonest; I had asked him a question with no numbers in it, so he answered with no numbers, and the inverter settled the bill for that vagueness at 2 a.m.
The tools I searched for online during that week failed me in two directions. Half of them listed American appliances my house has never owned. The other half announced a solar size with no load maths behind it at all. A Pakistani home needs its own list: the water motor, the inverter fan, the geyser, the two kinds of air conditioner. To this day I add the refrigerator's starting surge on top of any result by hand, and I read each nameplate figure twice before I trust a band, because the surge is the one number that caught me. That list lives in the tool above, and the guides below take each part of it, the surge, the meter, the installer quote, and give it the space it deserves.
Guides on home load, UPS and solar
- How I calculated my home load before buying a UPS, and what I got wrong first
- Inverter fans vs old ceiling fans: the watt difference on a real bill
- How many solar panels a 5 marla house in Pakistan actually needs
- Why your refrigerator keeps tripping the UPS at night
- 1 ton vs 1.5 ton inverter AC: the load and bill maths side by side
- How to read your electricity meter and find your real daily units
- Generator or UPS: which backup your load actually needs
- The hidden loads: small devices that burn units all day
- What a 1 HP water motor adds to your monthly electricity bill
- How to check a solar installer's quote against your own load sheet
Questions people ask about this page
Does this calculator work for a shop or an office?
Yes, within limits. The maths is the same: watts times hours gives units, and the size bands scale up. A shop with three-phase supply, large motors or a commercial tariff should take the load sheet to an electrician, since starting currents and phase balance sit outside a home tool.
Why does the UPS size use only the items I marked for backup?
A UPS carries a home through loadshedding, not through a normal day. Air conditioners, irons and geysers usually stay off the backup line, so the inverter only needs the fans, lights, fridge and screens you marked. Sizing the UPS from the full connected load buys a bigger inverter than the house will ever ask for at 2 a.m.
How accurate are the preset watts in the appliance list?
The presets are typical Pakistan market values, and your own appliance can differ by 10 to 20 percent. The nameplate sticker on the appliance itself is the better figure, and every watt field in the tool is editable for that reason. For a bill-level estimate, a week of meter readings beats any preset.
What per-unit rate should I enter for a bill estimate?
Read the rate from your own last bill, since Pakistani tariffs move by slab and by distribution company. Divide the energy charge on the bill by the units consumed and enter that number. The tool then multiplies your monthly units by your rate and shows a planning estimate, not a tariff quote.
Can the suggested solar size run an air conditioner?
An inverter air conditioner, yes, in most cases, because an inverter unit ramps up gently. A non-inverter unit pulls a hard starting surge, and the system needs headroom above the running watts. The solar band here comes from your daily units, so add the AC hours honestly and let the band reflect them.
Facts, checked against trusted sources
- Standby power accounts for about 5 to 10 percent of residential energy use in US homes, per the US Department of Energy. Source: US Department of Energy
- LED bulbs use at least 75 percent less energy than incandescent lighting and last up to 25 times longer, per the US Department of Energy. Source: US Department of Energy
